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研究者情報

マスター

アカウント（マスター）

  • 氏名

    山口　篤(ヤマグチ　アツシ), ヤマグチ　アツシ

所属（マスター）

  • 水産科学研究院　海洋生物資源科学部門　海洋生物学分野

所属（マスター）

  • 水産科学研究院　海洋生物資源科学部門　海洋生物学分野

独自項目

syllabus

  • 2021, 洋上実習Ⅰ, Field Training on Board Ⅰ, 学士課程, 水産学部, 乗船実習　おしょろ丸　北太平洋西部　流し網　海洋観測　プランクトン　海水分析　サケ　外洋　生態系　目視調査　操船
  • 2021, 乗船実習, Shipboard Training, 学士課程, 水産学部, おしょろ丸、海洋観測、生物採集、目視観察
  • 2021, 海洋生物科学実験Ⅲ, Marine Science Biology III - Laboratory, 学士課程, 水産学部, 魚類、プランクトン、解剖、分類、形態、生態、生?、サケ
  • 2021, プランクトン学, Planktology, 学士課程, 水産学部, プランクトン生物、分布、生態、生理、生産、化学組成、同化効率、成長効率、栄養動態、環境変動、?潮・?毒
  • 2021, 海洋生物科学Ⅱ, Marine Biological Science Ⅱ, 学士課程, 水産学部, 海洋生態系、物質循環、プランクトン、ネクトン、ベントス

researchmap

プロフィール情報

所属

  • 北海道大学, 大学院水産科学院, 准教授
  • 北海道大学, 北極域研究センター, 准教授

学位

  • 博士（水産学）（1999年03月 北海道大学）

プロフィール情報

  • プロフィール

    海洋の動物プランクトン生態学を専門とし、特に亜寒帯域や寒帯域におけるカイアシ類の生活史、中・深層性カイアシ類の摂餌および物質循環に関する研究が多い。2015年からは北海道大学北極域研究センターの兼務教員として、北極域における気候変動が動物プランクトンに与える影響の評価研究も行っている。

  • 姓

    山口, ヤマグチ

  • 名

    篤, アツシ

  • ID各種

    A-8613-2012, 200901042590869310

対象リソース

所属

  • 北海道大学, 大学院水産科学院, 准教授
  • 北海道大学, 北極域研究センター, 准教授

業績リスト

研究キーワード

  • 極域生態系   深海生物学   動物プランクトン   カイアシ類   物質循環   環境動態解析   海洋生態系   生物海洋学   生物地球化学   

研究分野

  • 環境・農学 / 環境動態解析
  • ライフサイエンス / 水圏生産科学

経歴

  • 2015年04月 - 現在 北海道大学 北極域研究センター 准教授（兼務）
  • 2008年04月 - 現在 北海道大学大学院水産科学研究院 大学院水産科学院 准教授
  • 2018年03月 - 2019年03月 米国ウッズホール海洋学研究所 客員研究員
  • 2010年04月 - 2018年03月 国立研究開発法人 産業技術総合研究所 客員研究員
  • 2007年04月 - 2008年03月 北海道大学大学院水産科学研究院 大学院水産科学院 助教
  • 2002年04月 - 2007年03月 北海道大学 大学院水産科学研究院 助手
  • 1999年04月 - 2002年03月 株式会社 関西総合環境センター 社員

学歴

  • 1996年 - 1999年   北海道大学   大学院水産科学院   博士課程
  • 1994年 - 1996年   北海道大学   大学院水産科学院   修士課程
  • 1990年 - 1994年   北海道大学   大学院水産科学研究院   水産増殖学科

委員歴

  • 2023年05月 - 現在   Frontiers in Marine Science   Associate Editor
  • 2021年04月 - 現在   日本プランクトン学会報   編集長
  • 2019年 - 現在   Oceans   Editorial Board
  • 2014年 - 現在   Journal of Marine Science and Technology   Editorial Board
  • 2022年07月 - 2024年07月   国際カイアシ類学会   評議員
  • 2022年05月 - 2023年10月   第20回国際有害有毒藻類学会   科学委員会委員
  • 2022年02月 - 2023年05月   Frontiers in Marine Science   Review Editor
  • 2021年10月 - 2023年03月   第7回国際北極研究シンポジウム（ISAR-7）組織委員
  • 2019年04月 - 2023年03月   日本プランクトン学会   評議員
  • 2016年 - 2021年   日本プランクトン学会報   編集委員   日本プランクトン学会
  • 2013年 - 2019年   水産海洋学会   国際誌委員
  • 2014年 - 2017年   Fisheries Oceanography   Editorial Board
  • 2009年 - 2017年   日本プランクトン学会   評議員   日本プランクトン学会
  • 2011年 - 2015年   Plankton and Benthos Research Editorial Board   日本プランクトン学会
  • 2006年 - 2012年   PICES（北太平洋海洋科学機構）   BIO委員   PICES（北太平洋海洋科学機構）BIO委員
  • 2009年 - 2010年   Deep-Sea Research II   Guest Editor (Volume 57, Issues 17-18)
  • 2005年 - 2010年   日本プランクトン学会   幹事長   日本プランクトン学会

受賞

  • 2018年02月 第33回北方圏国際シンポジウム 青田昌秋賞
  • 2016年07月 米国沿岸警備隊 北極功労メダル
  • 2014年10月 PICES ベストポスタープレゼンテーションアワード（モニタリング分野）
  • 2014年10月 日本プランクトン学会 論文賞
  • 2013年10月 PICES ベストポスタープレゼンテーションアワード（生物海洋学分野）
  • 2012年03月 日本海洋学会 ベストポスター賞
  • 2011年04月 文部科学大臣表彰 若手科学者賞
     The Commendation for Science and Technology by the Minister of Education, Culture, Sports, Science and Technology
  • 2006年04月 日本海洋学会 岡田賞
     The Oceanographic Society of Japan
  • 2001年03月 日本プランクトン学会 奨励賞
     The Plankton Society of Japan

論文

  • Kohei Matsuno, Rikuto Sugioka, Yurika Maeda, Ryan Driscoll, Fokje L. Schaafsma, Sara Driscoll, Atsushi Yamaguchi, Ryuichi Matsukura, Hiroko Sasaki, Hiroto Murase
    Progress in Oceanography 229 103360 - 103360 2024年12月
  • Kosuke Egashira, Yu-Sin Huang, Kohei Matsuno, Atsushi Yamaguchi
    Bulletin of Fisheries Sciences, Hokkaido University 74 1 23 - 33 2024年08月 [査読無し][通常論文]
  • Li Wang, Xufa Ma, Dongwoo Kim, Kohei Matsuno, Atsushi Yamaguchi
    Bulletin of Fisheries Sciences, Hokkaido University 74 1 13 - 22 2024年08月 [査読無し][通常論文]
  • Koki Tokuhiro, Kohei Matsuno, Jonaotaro Onodera, Makoto Sampei, Amane Fujiwara, Naomi Harada, Barbara Niehoff, Eva-Maria Nöthig, Atsushi Yamaguchi
    Journal of Plankton Research 46 2 183 - 193 2024年01月22日 
    Abstract Calanus hyperboreus is one of the dominant copepod species in the Arctic zooplankton communities. The impact of climate change varies among regions within the Arctic, implying that C. hyperboreus populations may be differently affected at different locations, but knowledge on seasonal population dynamics in relation to biogeography is scarce. To fill this gap, we counted C. hyperboreus in samples from sediment traps that were moored from 2009 to 2014 in three regions of the Arctic Ocean (eastern Fram Strait, northern Chukchi Sea and MacKenzie Trough). The C. hyperboreus flux increased between April and May in all regions, likely associated with the ascent from overwintering depth to the surface. In the descent period, high fluxes were observed between July and September in the Fram Strait, between September and November in the northern Chukchi Sea, and between August and October in the MacKenzie Trough, suggesting that the timing of descent varied among the regions characterized by differences in light regime, phytoplankton development and water temperature. The copepodite stage composition in the eastern Fram Strait and the MacKenzie Trough varied with season, suggesting successful local reproduction while it was uniform in the northern Chukchi Sea, possibly because the population is fueled by advection.
  • Kunito Yamamae, Yasuhide Nakamura, Kohei Matsuno, Atsushi Yamaguchi
    Progress in Oceanography 219 103155 - 103155 2023年12月 [査読有り][通常論文]
  • Shino Kumagai, Kohei Matsuno, Atsushi Yamaguchi
    Frontiers in Marine Science 10 1233492 - 1233492 2023年11月29日 [査読有り][通常論文]
     
    Drastic environmental changes were noted in the northern Bering Sea in 2018. A reduction in sea ice affected several trophic levels within the ecosystem; this resulted in delayed phytoplankton blooms, the northward shifting of fish stocks, and a decrease in the number of seabirds. Changes in the community composition of zooplankton were reported in 2022, but changes in zooplankton interactions and production have not been reported to date. Therefore, this study examined predator-prey interaction, secondary production, and prey availability for fish to understand the effect of early sea ice melt. Zooplankton size data were estimated from the size spectra obtained using ZooScan based on samples collected in 2017 and 2018. A cluster analysis based on biovolume showed that the zooplankton community could be divided into three groups (Y2017N, Y2017S, Y2018). Y2017N, characterized by low abundance, biomass, and production, Y2017S, characterized by high biovolume and production, which contributed with Calanus spp., and Y2018, characterized by low biovolume but high production, contributed with small copepods, and Bivalvia. In 2017, the highest biovolume group was observed south of St. Lawrence Island, and it was dominated by Calanus spp. and Chaetognatha. Normalized size spectra of this group showed the highest secondary production with present predator-prey interactions, suggesting that the area provides high prey availability for fish larvae and juveniles. In contrast, small copepods and bivalve larvae were dominant in this area in 2018, which contain less carbons and energy, suggesting the prevalence of low-nutrient foods in this year in relation to early sea ice melt.
  • Kohei Matsuno, Kohei Sumiya, Manami Tozawa, Daiki Nomura, Hiroko Sasaki, Atsushi Yamaguchi, Hiroto Murase
    Progress in Oceanography 218 103117 - 103117 2023年11月 [査読有り][通常論文]
  • Yasuhide Nakamura, Hiryori Itagaki, Akihiro Tuji, Shinji Shimode, Atsushi Yamaguchi, Kiyotaka Hidaka, Eri Ogiso‐Tanaka
    Environmental Microbiology 2023年10月18日 [査読有り][通常論文]
     
    Abstract DNA metabarcoding on a single organism is a promising approach to clarify the biological interactions (e.g., predator–prey relationships and symbiosis, including parasitism) of difficult‐to‐culture protists. To evaluate the effectiveness of this method, Radiolaria and Phaeodaria, which are ecologically important protistan groups, were chosen as target taxa. DNA metabarcoding on a single organism focused on the V9 region of the 18S rRNA gene revealed potential symbionts, parasites and food sources of Radiolaria and Phaeodaria. Previously reported hosts and symbionts (parasites) were detected, and newly recognized combinations were also identified. The contained organisms largely differed between Radiolaria and Phaeodaria. In Radiolaria, members of the same order tended to contain similar organisms, and the taxonomic composition of possible symbionts, parasites, and food sources was fixed at the species level. Members of the same phaeodarian family, however, did not contain similar organisms, and body part (i.e., the central capsule or the phaeodium) was the most important factor that divided the taxonomic composition of detected organisms, implying that the selection of appropriate body part is important when trying to ascertain contained organisms, even for unicellular zooplankton. Our results show that DNA metabarcoding on a single organism is effective in revealing the biological interactions of difficult‐to‐culture protists.
  • Igor Dovgal, Atsushi Yamaguchi, Daiki Kojima, Yoshinari Endo
    European Journal of Protistology 91 126036 - 126036 2023年10月 [査読有り][通常論文]
  • Minami Ishihara, Kohei Matsuno, Koki Tokuhiro, Yasuhiro Ando, Kazutoshi Sato, Atsushi Yamaguchi
    Frontiers in Marine Science 10 1168015 - 1168015 2023年09月20日 [査読有り][通常論文]
     
    Calanus glacialis/marshallae is a dominant zooplankton species in the Pacific Arctic Ocean that is widely distributed in shelf areas, and it plays a vital role in connecting primary production to higher trophic levels. Its phenology is well adapted to hydrography, but there is little available information about regional and diel changes in population structure and grazing features. In this study, we investigated C. glacialis/marshallae during autumn 2019 in the Eastern and Northeastern Chukchi and Canadian basins to reveal geographic and diel variations in population structure, body size, grazing activity, and fatty acid composition. The abundance of C. glacialis/marshallae was found to be high on the slopes and low on the shelves. Body size (prosome length) was well described by the Bělehrádek equation combined with in-situ temperature throughout the sampling region. Cluster analyses based on hydrographic parameters were divided into four regions: southern shelf, northern shelf, slope, and basin. The southern shelf was dominated by copepodite stage five (C5) transported from the Bering Sea by Pacific waters. C4 and C5 were dominant on the northern shelf, suggesting that they grew slower than those on the southern shelf, and the populations also exhibited higher concentrations of fatty acids originating from dinoflagellates than those originating from the pan-Arctic Ocean, indicating low productivity in the region. The population on the slope had the highest abundance, C4 was dominant, and large amounts of diatom-derived eicosapentaenoic acid (EPA). These features are attributed to the upwelling of populations and nutrients that support diatom growth. In the basin, the early copepodite stages of composition were distinctly higher than those recorded in previous studies, because larger amounts of organisms flow into the region, resulting in more extended reproduction periods. In the basin, small and large forms of C5 were simultaneously found, and the small form exhibited a diel grazing activity pattern, but the large forms did not. These findings suggest their well adaptation in changing of the Pacific Arctic Ocean.
  • Yunosuke Koguchi, Koki Tokuhiro, Carin J. Ashjian, Robert G. Campbell, Atsushi Yamaguchi
    Frontiers in Marine Science 10 2023年09月05日 [査読有り][通常論文]
  • Yuya Nakamura, Haochen Zhang, Atsushi Yamaguchi
    Oceans 4 3 253 - 268 2023年07月31日 [査読有り][通常論文]
     
    In the oceans, Chaetognatha can contribute significantly to the total zooplankton biomass (up to 10–30%). The genus Eukrohnia, the dominant Chaetognath genus in the western subarctic Pacific, includes E. hamata and E. bathypelagica. Although it has been pointed out that there is no genetic difference between the two species, no study has been made that treats them as the same species group. In this study, we investigated vertical distribution based on the eight vertical stratification samplings down to 1000 m depths conducted day/night at four seasons covering one year, community structure, and population structure of the three dominant Chaetognath species: Parasagitta elegans, E. hamata, and E. bathypelagica in the western subarctic Pacific. The population densities of each species at 0–1000 m water column were 0.04–0.36 ind. m−3 for P. elegans, 0.14–1.60 ind. m−3 for E. hamata, 0.24–1.54 ind. m−3 for E. bathypelagica, and 1.37–2.62 ind. m−3 for Eukrohnia juveniles. The vertical distributions were consistent both day and night, and no diel changes were observed for all species throughout the seasons. The vertical distribution of Chaetognaths evaluated by the distribution center was 61–169 m for P. elegans, 143–206 m for Eukrohnia juveniles, 134–279 m for E. hamata, and 253–612 m for E. bathypelagica. The body length of P. elegans ranged from 4 to 34 mm, and one to three cohorts were identified at each sampling occasion. While the presence of the eight stages has been reported for Eukrohnia, only one to five stages occurred, and specimens belonging to six to eight stages were not observed in the samples throughout the year. The body length of the whole Eukrohnia species ranged from 2 to 14 mm. The body length histograms of the Eukrohnia species group, including E. hamata and E. bathypelagica, and their juveniles showed the presence of two to four cohorts at each sampling date. Within the Eukrohnia species group, vertical changes in body length were present, which were characterized by the smaller specimens occurring at shallower depths, followed by an increase in body length with increasing depths. From the vertical distribution and population structure of the Eukrohnia species group (Eukrohnia juvenile + E. hamata + E. bathypelagica) in this study, there was no difficulty in treating them as one species. It may suggest that E. hamata and E. bathypelagica in the western subarctic Pacific could be treated as one species group. To clarify this point, a detailed genetic analysis of the Eukrohnia species group will be needed for future studies.
  • Mari Aizawa, Tian Gao, Atsushi Yamaguchi
    Oceans 4 3 242 - 252 2023年07月31日 [査読有り][通常論文]
     
    Hydrozoans are numerically dominant taxa in gelatinous zooplankton communities of the worldwide oceans and play an energy transfer role connecting primary producers and higher trophic level organisms. In the western subarctic Pacific, St. K2 has been established as a long-term time-series monitoring station. Various studies on zooplankton have been conducted, while hydrozoans have not been treated. This study presents the abundance, vertical distribution, and population structure of the dominant hydrozoan species (Aglantha digitale) at St. K2. Samples collected by vertical stratification samplings from eight layers of 0–1000 m both day and night during four seasons in one year. Hydrozoans occur throughout the year. The annual mean abundance of A. digitale was 198.4 ind. m−2 and composed of 91.9% of hydrozoans. The vertical distribution of A. digitale was concentrated for the epipelagic layer (0–200 m), both day and night of the most season. The bell height (BH) of A. digitale ranged between 2.4–18.9 mm. Most of the mature individuals, with gonad length larger than 10% of BH, occurred only in July. The BH of mature individuals ranged from 4.7 to 17.6 mm, with the BH of most mature individuals were larger than >10 mm. Through observation on BH at each sampling layer, small individuals with BH < 6 mm were distributed below 300 m depths throughout the seasons, expanding their vertical distribution to the deeper layers. Inter-region comparison of abundance, maturation body size, and generation length of A. digitale revealed that these parameters are varied with the region and depend on the marine ecosystem structures.
  • Dongwoo Kim, Kanako Amei, Sota Komeda, Koki Tokuhiro, Maki Noguchi Aita, Fujio Hyodo, Atsushi Yamaguchi
    Deep Sea Research Part I: Oceanographic Research Papers 197 104045 - 104045 2023年07月 [査読有り][通常論文]
  • Yunosuke Koguchi, Koki Tokuhiro, Carin J. Ashjian, Robert G. Campbell, Atsushi Yamaguchi
    Crustaceana 96 6 601 - 602 2023年06月16日 [査読有り][通常論文]
  • Kanako Amei, Ryo Dobashi, Minoru Kitamura, Atsushi Yamaguchi
    Journal of Plankton Research 45 4 661 - 676 2023年06月13日 [査読有り][通常論文]
     
    Abstract Information on pelagic polychaete community structure in the western North Pacific is available for the subarctic region (Station K2) but not for the subtropical region. Hence, we analyzed day–night vertically stratified samples collected in eight layers within the first 1000 m of the water column during four seasons in 1 year, using the same sampling method as St. K2, at the subtropical region (Station S1). At St. S1, 27 species of pelagic polychaetes belonging to 13 genera and six families were identified. The annual mean abundance was 35.0 ind. 1000 m−3 and the biomass was 17.3 mg WW 1000 m−3. At St. S1, the numbers of genera and species were higher and the annual mean abundance and biomasses were much lower than St. K2. The pelagic polychaetes often peaked in the mesopelagic layer at St. K2, with the carnivores and particle feeders peaking in the epipelagic and mesopelagic layers, respectively. At St.S1, the carnivorous species predominated throughout the entire water column, and were most abundant in the epipelagic layer. Thus, In the western Pacific Ocean, the subarctic pelagic polychaete community structure changed vertically with feeding ecology. On the other hand, the subtropical community may be adapted to conditions of high irradiance and light transmission.
  • Ryo Taniguchi, Kanako Amei, Koki Tokuhiro, Yuichiro Yamada, Minoru Kitamura, Atsushi Yamaguchi
    Journal of Plankton Research 45 3 554 - 570 2023年05月26日 [査読有り][通常論文]
     
    Abstract Vertically stratified day and night samples were collected from a depth of up to 1000 m during four seasons at a single station in the western subarctic Pacific. Subsequently, the abundance, biovolume, community structure and population structure of the pelagic amphipods were evaluated from the imaging analysis using ZooScan. The stable isotope ratio (δ15N) was also measured for each species. In total 10 amphipod species were identified in total, and their community structures were separated into four groups. The four communities were characterized by the upper-layer community dominated by Themisto pacifica, and the deep-water community that was characterized by the absence of T. pacifica. The other two groups were observed for the intermediate depths at night only, which was characterized by the low abundance of T. pacifica performing diel vertical migration from those depths. The deep-dwelling species displayed higher δ15N and positive relationships were detected with the habitat depth of each species. For the predominant T. pacifica, population structure (cohort) analysis was possible based on equivalent spherical diameter data from ZooScan. This study demonstrates that imaging analysis by ZooScan is applicable for analyses of minor taxonomic groups (amphipods) in zooplankton communities.
  • Yunosuke Koguchi, Koki Tokuhiro, Carin J. Ashjian, Robert G. Campbell, Atsushi Yamaguchi
    Crustaceana 96 2 113 - 129 2023年02月22日 [査読有り][通常論文]
     
    Abstract Aetideid copepods dominate the mesopelagic layer of the Arctic Ocean and play an important role in the vertical material flux and biodiversity. However, little information about the lengths and weights of their copepodids is available. In this study, we collected five sympatric aetideid copepods, Chiridius obtusifrons Sars G.O., 1902, Gaetanus tenuispinus (Sars G.O., 1900), Gaetanus brevispinus (Sars G.O., 1900), Aetideopsis multiserrata (Wolfenden, 1904), and Aetideopsis rostrata Sars G.O., 1903, from the Arctic Ocean and examined their body lengths, dry and ash-free dry weights, and developmental growths at each copepodid stage. Highly significant length-weight relationships were obtained among copepodids for all species. Within genera, individuals of the same length were heavier at shallower depths. This may result from the greater nutritional availability to species within genera inhabiting shallower depths. Common to all species, the organic content (ash-free dry weight per dry weight) was high for the early copepodid stages. This may be due to the residual organic content of lipid-rich eggs retained in the non-feeding nauplii. The largest growth in females occurred at C5/C6, whereas the largest growth in males occurred at C4/C5, as determined by moult increment and proportion of growth in weight. These sex differences in weight growth could be due to the degeneration of the feeding appendage and cessation of feeding in C6 males of aetideid copepods.
  • Yoshinari Endo, Yuma Sato, Atsushi Yamaguchi, Igor Dovgal
    Plankton and Benthos Research 17 4 393 - 405 2022年11月30日 [査読有り][通常論文]
  • Takumi Teraoka, Kanako Amei, Yutaka Fukai, Kohei Matsuno, Hiroji Onishi, Atsushi Ooki, Tetsuya Takatsu, Atsushi Yamaguchi
    Plankton and Benthos Research 17 4 369 - 382 2022年11月30日 [査読有り]
  • Naoya Kanna, Shin Sugiyama, Takuto Ando, Yefan Wang, Yuta Sakuragi, Toya Hazumi, Kohei Matsuno, Atsushi Yamaguchi, Jun Nishioka, Youhei Yamashita
    Global Biogeochemical Cycles 36 11 2022年11月 [査読有り]
  • Fukai, Yutaka, Chiba, Sanae, Batten, Sonia, Sasaki, Yuka, Matsuno, Kohei, Richardson, Anthony J, Yamaguchi, Atsushi
    Bulletin of Fisheries Sciences, Hokkaido University 72 2 17 - 26 2022年08月22日 [査読無し][通常論文]
  • Yunosuke Koguchi, Koki Tokuhiro, Carin J. Ashjian, Robert G. Campbell, Atsushi Yamaguchi
    Frontiers in Marine Science 9 943100 - 943100 2022年08月19日 [査読有り][通常論文]
     
    Aetideidae is a calanoid copepod family dominant in the mesopelagic layer of the Arctic Ocean for which little ecological information is available because species identification, especially of early copepodite stages, is difficult. In this study, we developed a species identification flow for the whole copepodite stages of five sympatric aetideid copepods (Chiridius obtusifrons, Gaetanus tenuispinus, G. brevispinus, Aetideopsis multiserrata, and A. rostrata). Vertical distributions and seasonal population structures of these species were evaluated using a year-round sample time-series collected at the drifting ice station (SHEBA) in the western Arctic Ocean. Combinations of morphological characteristics (prosome length, cephalosome, and prosome widths) were used to identify the early copepodite stages to species. Aetideopsis rostrata was distributed in deep waters (1,032–1,065 m) throughout the year. The other species all were found at 600–700 m during the midnight sun. However, during the polar night, the vertical distributions of each species were distinct, resulting from ascent, descent, or depth maintenance, indicating seasonal vertical migration which may function to reduce inter-specific competition during the polar night when food resources are scarce. Reproduction timing varied among four aetideid copepods: C.obtusifrons and G. tenuispinus showed polar night ascent and reproduction at the end of the polar night, whereas G. brevispinus and A. multiserrata showed descent or depth maintenance during the polar night and reproduction at the beginning of the polar night. There was not sufficient data to examine reproduction timing of A. rostrata. Common for all aetideid species, δ15N values of the adult females indicate more carnivorous feeding modes during the polar night than those in the midnight sun. Such vertical distribution and timing of reproduction variation among these five aetideid copepods may function to reduce species competition in the mesopelagic layer of the Arctic Ocean.
  • Daiki Kojima, Yusuke Hamao, Kanako Amei, Yutaka Fukai, Kohei Matsuno, Yoko Mitani, Atsushi Yamaguchi
    Deep Sea Research Part I: Oceanographic Research Papers 185 103771 - 103771 2022年07月 [査読有り][通常論文]
  • 2021年秋季北海道太平洋沿岸における有害赤潮藻Karenia selliformisの 水平分布および植物プランクトンの群集構造
    山口 篤, 濱尾優介, 松野孝平, 飯田高大
    水産海洋研究 86 2 41 - 49 2022年05月 [査読有り][通常論文]
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  • Atsushi Yamaguchi, Carin J Ashjian, Robert G Campbell
    Journal of Plankton Research 44 443 - 453 2022年04月23日 [査読有り]
     
    Abstract In the Arctic Ocean, the life cycles of interzonal omnivorous copepods have been studied, whereas little information is available on the life cycles of mesopelagic carnivorous species. Here, the life cycles of two mesopelagic carnivorous copepods (Paraeuchaeta glacialis and Heterorhabdus norvegicus) are described from vertically stratified samples collected at an annual ice-station (SHEBA) in the western Arctic Ocean during 1996–1997. Reproduction estimated to occur between January and March for both species. Vertical distributions and population growth varied between the species. Early copepodite stages and adult males of P. glacialis were distributed in deeper layers, whereas late copepodite stages and adult females were observed in shallower layers. The skewed sex ratio towards females was observed for adults, which may be related to the cease feeding and short longevity for adult males. In contrast, all the H. norvegicus life stages were distributed in the mesopelagic layer. Clear peaks of the young stages and their sequence suggest that H. norvegicus may complete its life cycle within 1 year. A specialized feeding mode (incorporating a venomous injection spine and large beak) could be a key trait facilitating the achievement of rapid growth in H. norvegicus in the food-limited mesopelagic layer.
  • Yusuke Hamao, Kohei Matsuno, Yoko Mitani, Atsushi Yamaguchi
    Journal of Oceanography 78 2 89 - 101 2022年04月 [査読有り]
     
    Abstract The southern part of the Okhotsk Sea off Hokkaido has rich fishery resources supported by high primary production. The phytoplankton community has been described by several studies based on size-fractionated chlorophyll a concentration and primary production; however, the details of the species composition of nano- and micro-protist communities have not been well investigated. We evaluated the spatial distribution and relationship with hydrography of nano- and micro-protist communities in the southern region of the Okhotsk Sea off Hokkaido during the summer of 2019. Forty-two species of diatoms from 19 genera, dinoflagellates from 7 genera, tintinnid ciliates, oligotrich ciliates, and 1 genus of silicoflagellates were identified. Their spatial distribution showed distinct differences among the taxa. Cluster analysis based on the protist cell density identified six groups with geographically well-distinguished distributions. Diatom-dominant communities were distributed in the Cold Water Belt and Soya warm current along the coastal area of Hokkaido. Nanoflagellate-dominated communities were distributed in the offshore area. Some harmful species of diatoms (Pseudonitzschia pseudodelicatissima) and dinoflagellates (Alexandrium spp.) were dominant in the Cold Water Belt off Wakkanai. We suggest that the upwelling of cold water could increase the abundance of harmful species, with immanent negative impacts on marine ecosystems or fishery resources. In summary, the species composition and abundance of the summer protist community was strongly related to different water masses in the southern part of the Okhotsk Sea off Hokkaido.
  • Fumihiko Kimura, Kohei Matsuno, Yoshiyuki Abe, Atsushi Yamaguchi
    Frontiers in Marine Science 9 2022年02月22日 [査読有り]
     
    A remarkable early sea-ice reduction event was observed in the northern Bering Sea during 2018. In turn, this unusual hydrographic phenomenon affected several marine trophic levels, resulting in delayed phytoplankton blooms, phytoplankton community changes, and a northward shift of fish stocks. However, the response of the zooplankton community remains uncharacterized. Therefore, our study sought to investigate the zooplankton community shifts in the northern Bering Sea during the summers of 2017 and 2018 and evaluate the effects of early sea-ice melt events on the zooplankton community, population structure of large copepods, and copepod production. Five zooplankton communities were identified based on cluster analysis. Further, annual changes in the zooplankton community were identified in the Chirikov Basin. In 2017, the zooplankton community included abundant Pacific copepods transported by the Anadyr water. In 2018, however, the zooplankton community was dominated by small copepods and younger stages of large copepods (Calanus glacialis/marshallae and Metridia pacifica), which was likely caused by reproduction delays resulting from the early sea-ice reduction event. These environmental abnormalities increased copepod production; however, this higher zooplankton productivity did not efficiently reach the higher trophic levels. Taken together, our findings demonstrated that zooplankton community structure and production are highly sensitive to the environmental changes associated with early sea-ice reduction (e.g., warm temperatures and food availability).
  • Bungo Nishizawa, Jumpei Okado, Yoko Mitani, Tomohiro Nakamura, Atsushi Yamaguchi, Tohru Mukai, Yutaka Watanuki
    Fisheries Science 88 1 109 - 118 2022年01月 [査読有り]
     
    To understand the environmental factors affecting the density of foraging seabirds across the cold-water belt in the southwestern Okhotsk Sea, we conducted a 1-day (180-km transect length) shipboard seabird survey off the northeastern coast of Hokkaido during summer in 2019, along with acoustic observations of potential prey (zooplankton and fish) biomass, thermosalinograph measurements, and CTD observations. Planktivorous short-tailed shearwaters Ardenna tenuirostris (66% of total seabirds) and piscivorous rhinoceros auklets Cerorhinca monocerata (28%) were predominant, but foraged in contrasting habitats. A large foraging flock of shearwaters was observed in the cold-water belt zone, including its front with coastal Soya Warm Current Water and the offshore Fresh Surface Okhotsk Sea Water, where surface chlorophyll a concentrations were the highest but not related to their prey (zooplankton) biomass at any spatial scale between 4.6 and 9.2 km. In contrast, the density of auklets was high in the coastal Soya Warm Current Water, where the acoustically determined fish biomass was large, and showed a positive relationship with the fish biomass especially in the lower layer (29–104 m depth) at any spatial scale. This species-specific difference in response to prey biomass might be related to prey-searching behaviors; i.e., rhinoceros auklets search prey underwater visually, but short-tailed shearwater can use both visual and olfactory cues to locate zooplankton patches from the air.
  • 小林淳希, 宮下洋平, 大洞裕貴, 織田さやか, 田中邦明, 松野孝平, 山口篤, 今井一郎
    北海道大学水産科学研究紀要 60 33 - 67 2021年12月 [査読無し][通常論文]
  • Max D. Campbell, David S. Schoeman, William Venables, Rana Abu‐Alhaija, Sonia D. Batten, Sanae Chiba, Frank Coman, Claire H. Davies, Martin Edwards, Ruth S. Eriksen, Jason D. Everett, Yutaka Fukai, Mitsuo Fukuchi, Octavio Esquivel Garrote, Graham Hosie, Jenny A. Huggett, David G. Johns, John A. Kitchener, Philippe Koubbi, Felicity R. McEnnulty, Erik Muxagata, Clare Ostle, Karen V. Robinson, Anita Slotwinski, Kerrie M. Swadling, Kunio T. Takahashi, Mark Tonks, Julian Uribe‐Palomino, Hans M. Verheye, William H. Wilson, Marco M. Worship, Atsushi Yamaguchi, Wuchang Zhang, Anthony J. Richardson
    Ecography 44 9 1283 - 1295 2021年09月 [査読有り][通常論文]
  • North-south changes of zooplankton community and copepods population along the 110°E line in the Indian sector of the Southern Ocean during the austral summer
    Sugioka, Rikuto, Matsuno, Kohei, Takahashi, Keigo D, Makabe, Ryosuke, Takahashi, Kunio T, Moteki, Masato, Odate, Tsuneo, Yamaguchi, Atsushi
    Bulletin of Fisheries Sciences, Hokkaido University 71 1 39 - 50 2021年08月 [査読無し][通常論文]
  • Impacts of diel vertical migration of the copepod Metridia pacifica on primary production and respiratory carbon flux in the subarctic Pacific Ocean
    Atsushi Yamaguchi
    Bulletin of Fisheries Sciences, Hokkaido University 71 1 29 - 37 2021年08月 [査読無し][通常論文]
  • Yasuhide Nakamura, Akihiro Tuji, Katsunori Kimoto, Atsushi Yamaguchi, Rie S. Hori, Noritoshi Suzuki
    Protist 172 3 125808 - 125808 2021年07月 [査読有り]
     
    The phylogenetic affiliation of Oroscenidae, a family of Radiolaria possessing large siliceous skeletons, was thoroughly revised in this study. Plankton sampling was conducted over seven years in seven sea areas of the Northern Hemisphere. Molecular analyses on the obtained specimens revealed that living oroscenids are phylogenetically different from hitherto-known radiolarian orders. The detailed examinations by Microfocus X-ray Computed Tomography and Scanning Electron Microscopy clarified that oroscenids and the related family (Thalassothamnidae) have unique skeletal characteristics different from other radiolarian orders. Judging from their phylogenetic distinctiveness and the difference in the morphology and ecology, Oroscenidae and Thalassothamnidae should be classified in a single order distinct from other radiolarian orders, and consequently, a new order, Orodaria, is established. (C) 2021 Elsevier GmbH. All rights reserved.
  • Kanako Amei, Ryo Dobashi, Naoto Jimi, Minoru Kitamura, Atsushi Yamaguchi
    Journal of Plankton Research 43 3 442 - 457 2021年05月27日 [査読有り]
     
    Abstract Pelagic polychaetes are distributed from the sea surface to greater depths of the oceans worldwide, but little information is available regarding their ecology. This study investigated the vertical distribution of abundance, biomass and community structure of pelagic polychaetes at a single station in the western subarctic Pacific based on day–night vertical stratified samples collected from a 0 to 1000 m water column during four seasons covering 1 year. The polychaete abundance and biomass ranged from 0 to 757 ind. 1000 m−3 and 0–6.1 mg WW m−3, respectively. Ten pelagic polychaete species belonging to nine genera and six families were identified. From cluster analysis based on abundance, the polychaete community was divided into five communities. Each community occurred at different depth layers. Two surface groups seen at 0–200 m were dominated by two carnivorous species: Tomopteris septentrionalis and Typhloscolex muelleri. The deepest group, dominated by the particle feeder Pelagobia longicirrata, was seen at 500–1000 m. Two transition groups occurred in the intermediate depths. These vertical distributions of the pelagic polychaete communities were common throughout the season and day. Water mass, food availability and the oxygen minimum layer are put forth as environmental factors that affect the pelagic polychaete community.
  • Takuma Matsumoto, Kohei Matsuno, Seiji Katakura, Hiromi Kasai, Atsushi Yamaguchi
    Regional Studies in Marine Science 43 101683 - 101683 2021年03月 [査読有り][通常論文]
  • Shin Sugiyama, Naoya Kanna, Daiki Sakakibara, Takuto Ando, Izumi Asaji, Ken Kondo, Yefan Wang, Yoshiki Fujishi, Shungo Fukumoto, Evgeniy Podolskiy, Yasushi Fukamachi, Minori Takahashi, Sumito Matoba, Yoshinori Iizuka, Ralf Greve, Masato Furuya, Kazutaka Tateyama, Tatsuya Watanabe, Shintaro Yamasaki, Atsushi Yamaguchi, Bungo Nishizawa, Kohei Matsuno, Daiki Nomura, Yuta Sakuragi, Yoshimasa Matsumura, Yoshihiko Ohashi, Teruo Aoki, Masashi Niwano, Naotaka Hayashi, Masahiro Minowa, Guillaume Jouvet, Eef van Dongen, Andreas Bauder, Martin Funk, Anders Anker Bjørk, Toku Oshima
    Polar Science 27 100632 - 100632 2021年03月 [査読有り]
     
    Environments along the coast of Greenland are rapidly changing under the influence of a warming climate in the Arctic. To better understand the changes in the coastal environments, we performed researches in the Qaanaaq region in northwestern Greenland as a part of the ArCS (Arctic Challenge for Sustainability) Project. Mass loss of ice caps and marine-terminating outlet glaciers were quantified by field and satellite observations. Measurements and sampling in fjords revealed the important role of glacial meltwater discharge in marine ecosystems. Flooding of a glacial stream in Qaanaaq and landslides in a nearby settlement were investigated to identify the drivers of the incidents. Our study observed rapid changes in the coastal environments, and their critical impact on the society in Qaanaaq. We organized workshops with the residents to absorb local and indigenous knowledge, as well as to share the results and data obtained in the project. Continuous effort towards obtaining long-term observations requiring involvement of local communities is crucial to contribute to a sustainable future in Greenland.
  • Atsushi Yamaguchi, Fumihiko Kimura, Yuri Fukai, Yoshiyuki Abe, Kohei Matsuno, Atsushi Ooki, Toru Hirawake
    Polar Science 27 100555 - 100555 2021年03月 [査読有り]
     
    In the northern Bering Sea, ice coverage and retreat timing were low and early, respectively, in the 2017?2018 winter. To evaluate the effect of these anomalous ice conditions, we quantified various environmental parameters (temperature, salinity, mixed-layer depth, nutrients) and the standing stocks of various planktonic taxa (phytoplankton counts, meso- and macrozooplankton mass, jellyfish abundance) during July of 2017 and 2018. For each year, the interaction between each parameter was evaluated by structural equation modelling (SEM) analysis. Large yearly differences were detected for the interactions between environmental parameters and planktonic stocks. Thus, for 2017, a total of fifteen interactions were present between environmental parameters and various planktonic stocks. In 2018, however, only eight interactions were present. Among the interactions, four were common to the two years. It is notable that the path coefficients of these four interactions were all lower in 2018 than in 2017. These findings suggest that the small magnitude and short pulse of the phytoplankton bloom in 2018 may have failed to transfer production and energy to a higher trophic level even within the planktonic food web. Indeed, in 2018, mass mortality was reported for seabirds (two murre species) feeding on planktivorous fishes.
  • Toru Hirawake, Masaki Uchida, Hiroto Abe, Irene D. Alabia, Tamotsu Hoshino, Shota Masumoto, Akira S. Mori, Jun Nishioka, Bungo Nishizawa, Atsushi Ooki, Akinori Takahashi, Yukiko Tanabe, Motoaki Tojo, Masaharu Tsuji, Hiromichi Ueno, Hisatomo Waga, Yuuki Y. Watanabe, Atsushi Yamaguchi, Youhei Yamashita
    Polar Science 27 100533 - 100533 2021年03月 [査読有り]
     
    Arctic ecosystems are altered profoundly by climate changes. However, the responses of Arctic marine and terrestrial ecosystems as well as their biodiversity to global warming remain largely unknown. This article provides comprehensive insights into the results and major findings from the Arctic Challenge for Sustainability (ArCS) Project ? an Arctic region research program initiated in Japan, which aims to address and advance our understanding of these uncertainties. Marine ecosystem studies have identified several biogeochemical processes that are associated with sea ice decline and northward transport and shift of marine species across multiple trophic levels over the Bering and Chukchi Sea shelves. Studies of the terrestrial ecosystem have identified factors that are important for the understanding of terrestrial biodiversity and ecosystems, including Arctic lakes, under the presence of global warming. Novel fungal species from the Arctic terrestrial ecosystem have also been isolated and described. Overall, these results could contribute to the conservation and sustainable management of the Arctic ecosystem services.
  • Kanako Amei, Naoto Jimi, Minoru Kitamura, Naoya Yokoi, Atsushi Yamaguchi
    Zoosymposia 19 1 41 - 50 2020年12月28日 [査読有り]
     
    Community structure and seasonal changes in the population structure of pelagic polychaetes were studied based on zooplankton samples collected by sediment traps moored at 200 m depth in the subarctic and subtropical western North Pacific throughout the year. Eight species belonging to seven genera and seven families occurred at the subarctic station, while twelve species belonging to ten genera and seven families were identified at the subtropical station. Polychaete abundance was 5.37 ± 0.44 ind. m-2 day-1 (annual mean ± standard error) at the subarctic station, and 1.36 ± 0.15 ind. m-2 day-1 at the subtropical station. Polychaete abundance at the subarctic station was high from May to August, but no seasonal patterns were observed at the subtropical station. The dominant species in the subarctic was Tomopteris septentrionalis, which accounted for 62.9% of annual mean abundance; at the subtropical station, the dominant species was Pelagobia sp. (22.8%). In the subarctic, small specimens of T. septentrionalis (<3 mm in body length) occurred only in winter (December-March). No clear seasonal changes in population structure of the subtropical Pelagobia sp. were detected. The latitudinal patterns we observed in the polychaete communities of the western North Pacific were similar to those previously observed in the eastern North Pacific. Changes in the population structure of T. septentrionalis suggest that the life cycle of this species is seasonal in the subarctic region.
  • Yuka Onishi, Akihiro Tuji, Atsushi Yamaguchi, Ichiro Imai
    Applied Sciences 11 1 172 - 172 2020年12月27日 [査読有り]
     
    The distribution of growth-inhibiting bacteria (GIB) against the toxic dinoflagellate Alexandrium catenella (Group I) was investigated targeting seagrass leaves and surface waters at the seagrass bed of Akkeshi-ko Estuary and surface waters of nearshore and offshore points of Akkeshi Bay, Japan. Weekly samplings were conducted from April to June in 2011. GIBs were detected from surface of leaves of the seagrass Zostera marina in Akkeshi-ko Estuary (7.5 × 105–4.7 × 106 colony-forming units: CFU g−1 wet leaf) and seawater at the stations in Akkeshi Bay (6.7 × 100–1.1 × 103 CFU mL−1). Sequence analyses revealed that the same bacterial strains with the same 16S rRNA sequences were isolated from the surface biofilm of Z. marina and the seawater in the Akkeshi Bay. We therefore strongly suggested that seagrass beds are the source of algicidal and growth-inhibiting bacteria in coastal ecosystems. Cells of A.catenella were not detected from seawaters in Akkeshi-ko Estuary and the coastal point of Akkeshi Bay, but frequently detected at the offshore point of Akkeshi Bay. It is suggested that A.catenella populations were suppressed by abundant GIBs derived from the seagrass bed, leading to the less toxin contamination of bivalves in Akkeshi-ko Estuary.
  • Bungo Nishizawa, Nodoka Yamada, Haruka Hayashi, Charlie Wright, Kathy Kuletz, Hiromichi Ueno, Tohru Mukai, Atsushi Yamaguchi, Yutaka Watanuki
    Deep Sea Research Part II: Topical Studies in Oceanography 181-182 104898 - 104898 2020年12月 [査読有り]
     
    To understand the effect of an unusually early sea-ice retreat in the northern Bering Sea in the spring of 2018 on the marine ecosystem of the northern Bering Sea, we compared at-sea observations of seabird density and acoustic observations of prey (fish and zooplankton) biomass during shipboard surveys around St. Lawrence Island in the summers of 2017 and 2018. Densities of foraging seabirds in 2018 (piscivorous divers: 4.7 birds km−2, planktivorous divers: 5.1, shearwaters: 0.7, surface feeders: 6.6) were lower than those in 2017 (piscivorous divers: 14.7 birds km−2, planktivorous divers: 10.3, shearwaters: 11.9, surface feeders:11.9). Acoustically-determined prey biomass in 2018 (fish: 6.4 m2nmi−2, zooplankton: 2.3) was also lower than in 2017 (fish: 18.4 m2nmi−2, zooplankton: 5.5). Similarly, biomass of macrozooplankton (amphipods, euphausiids, Neocalanus spp. and Calanus marshallae) sampled using bongo nets was smaller in 2018. At scales of 5–30 km, correlations between the seabird density and prey biomass were weaker (−0.2–0.3 of Pearson's r) in 2018 than those in 2017 (0.4–0.9) for all seabirds except planktivorous divers. We suggest that the lack of sea ice, and the resulting lack of ice-edge phytoplankton blooms, may weaken trophic linkages by causing a low biomass of secondary consumers and hence a reduced density of seabirds.
  • Marie Maekakuchi, Kohei Matsuno, Jun Yamamoto, Yoshiyuki Abe, Atsushi Yamaguchi
    Deep Sea Research Part II: Topical Studies in Oceanography 181-182 104818 - 104818 2020年12月 [査読有り]
  • Fumihiko Kimura, Yoshiyuki Abe, Kohei Matsuno, Russell R. Hopcroft, Atsushi Yamaguchi
    Deep Sea Research Part II: Topical Studies in Oceanography 181-182 104901 - 104901 2020年12月 [査読有り]
  • Yuri Fukai, Yoshiyuki Abe, Kohei Matsuno, Atsushi Yamaguchi
    Deep Sea Research Part II: Topical Studies in Oceanography 181-182 104903 - 104903 2020年12月 [査読有り]
  • Kajihara Hiroshi, Yamaguchi Atsushi
    Plankton and Benthos Research 15 4 337 - 341 日本プランクトン学会、日本ベントス学会 2020年11月18日 [査読有り]
     

    The three currently recognized species comprising the pelagic polystiliferous hoplonemertean genus Protopelagonemertes Brinkmann, 1917 are supposedly distinguishable chiefly with respect to the number of proboscis nerves: 29 (varying from 22 to 30) in P. hubrechti (Brinkmann, 1917); 19–21 (varying from 19 to 22) in P. beebei Coe, 1936; and 36 in P. joculatori Van der Spoel, 1988. A single specimen collected off the Pacific coast of Hokkaido, Japan, herein identified as P. beebei, was found to possess 19–23 primary proboscis nerves. In addition to the primary proboscis nerves, the material also possessed 12–16 secondary proboscis nerves, which are discernible from the primary nerves in that they coexist with putative glial cells. Although secondary proboscis nerves have been identified in some other species in the Pelagica, they have not previously been described for any members of the Protopelagonemertes. Our findings thus prompted us to question the validity of morphological species delimitation within this genus, given that the distinction between primary and secondary proboscis nerves has previously not been taken into consideration. Close examination of the specimen in the living state revealed that it is characterized by a pair of cephalic furrows, a structure commonly found in benthic representatives of the phylum, but herein confirmed for the first time among the Pelagica. A 658-bp partial sequence of the mitochondrial cytochrome c oxidase subunit I gene from the newly examined specimen was found to be identical to sequences derived from two other specimens previously collected in Sagami Bay, thereby indicating that P. beebei may occur commonly in Japanese meso- to bathypelagic waters.

  • Comparison of the vertical distribution of pelagic copepod abundance, biomass and community structure between the Atlantic and Pacific sectors of the Arctic Ocean
    Abe, Y, N. Hildebrandt, K. Matsuno, B. Niehoff, A. Yamaguchi
    Bulletin of Fisheries Sciences, Hokkaido University 70 1 91 - 102 2020年08月24日 [査読無し]
  • Vertical distribution, community structure, and active carbon flux of macrozooplankton taxa: amphipods and euphausiids in the summer of the western North Pacific
    Hanamiya, Y, H. Murase, K. Matsuno, A. Yamaguchi
    Bulletin of Fisheries Sciences, Hokkaido University 70 1 77 - 89 2020年08月24日 [査読無し]
  • Nobuharu Inaba, Isamu Kodama, Satoshi Nagai, Tomotaka Shiraishi, Kohei Matsuno, Atsushi Yamaguchi, Ichiro Imai
    Applied Sciences 10 16 5658 - 5658 2020年08月14日 [査読有り][通常論文]
     
    The intensity and frequency of harmful algal blooms (HABs) have increased, posing a threat to human seafood resources due to massive kills of cultured fish and toxin contamination of bivalves. In recent years, bacteria that inhibit the growth of HAB species were found to be densely populated on the biofilms of some macroalgal species, indicating the possible biological control of HABs by the artificial introduction of macroalgal beds. In this study, an artificially created Ulva pertusa bed using mobile floating cages and a natural macroalgal bed were studied to elucidate the distribution of algal growth-limiting bacteria (GLB). The density of GLB affecting fish-killing raphidophyte Chattonella antiqua, and two harmful dinoflagellates, were detected between 106 and 107 CFU g−1 wet weight on the biofilm of artificially introduced U. pertusa and 10 to 102 CFU mL−1 from adjacent seawater; however, GLB found from natural macroalgal species targeted all tested HAB species (five species), ranging between 105 and 106 CFU g−1 wet weight in density. These findings provide new ecological insights of GLB at macroalgal beds, and concurrently demonstrate the possible biological control of HABs by artificially introduced Ulva beds.
  • Yoshiyuki Abe, Kohei Matsuno, Amane Fujiwara, Atsushi Yamaguchi
    Progress in Oceanography 186 102391 - 102391 2020年07月 [査読有り][通常論文]
  • Koki Tokuhiro, Yoshiyuki Abe, Jonaotaro Onodera, Makoto Sampei, Amane Fujiwara, Naomi Harada, Kohei Matsuno, Eva-Maria Nöthig, Atsushi Yamaguchi
    Polar Science 24 100509 - 100509 2020年06月 [査読有り][通常論文]
  • K Matsuno, N Kanna, S Sugiyama, A Yamaguchi, EJ Yang
    Marine Ecology Progress Series 642 55 - 65 2020年05月28日 [査読有り][通常論文]
     
    To evaluate the effects of meltwater discharge from marine-terminating glaciers on a fjord protist community in northwestern Greenland during summer, we investigated the distribution, abundance and biomass of the protist community and their relationships with hydrographic parameters. In the standing stock of protists, dinoflagellates (46.4%) and oligotrich ciliates (39.5%) were dominant throughout the study region. With respect to vertical distribution, oligotrich ciliates were abundant in the surface layer, mainly due to suitable food conditions (abundance of diatom and nanoflagellates). Near glaciers, relatively high chlorophyll a (chl a) concentrations were found in the subsurface layers associated with the low-temperature, high-turbidity and slightly high nutrient levels, indicating that the nutrient inputs from the upwelling glacial meltwater plume increased primary production. Large-sized Protoperidium spp. were found only at stations near glaciers where nutrients were abundant, and heterotrophic dinoflagellates showed strong relationships with nanoflagellates. These findings suggest that the upwelling associated with subglacial meltwater discharge can stimulate nanoflagellate production, resulting in increases in ciliate and heterotrophic dinoflagellate production.
  • Yoshimi Tone Matsumoto, Atsushi Yamaguchi
    Plankton and Benthos Research 15 2 146 - 155 2020年05月27日 [査読有り][通常論文]
  • Atsushi Yamaguchi, Carin J Ashjian, Robert G Campbell, Yoshiyuki Abe
    Journal of Plankton Research 42 3 368 - 377 2020年05月27日 [査読有り][通常論文]
     
    Abstract Scaphocalanus magnus is a large copepod species with a worldwide distribution. Information on the ecology of this species is scarce. In this study, S. magnus was collected using vertically stratified net sampling from an ice station in the western Arctic Ocean over a year. The vertical distribution differed between periods of polar night and midnight sun, with core depth distributions of 264–381 m for the polar night and 518–745 m for the midnight sun. The shallower distribution during the polar night may have resulted from the animals moving upwards to find sufficient food during the less productive season. The abundance of early copepodite stages showed clear seasonality. The C2 and C3 stages were abundant June–August and August–September, respectively. After C4, seasonality in abundance was not clear. For C4 and C5, body sizes and masses were greater for males than for females while the opposite was the case for C6. Adult males do not feed and thus have shorter life spans than females, skewing the adult sex ratio towards females. For these mesopelagic particle feeding copepods, a long residence time at C6F suggests that in a varying food environment, it is possible to wait to initiate reproduction until favourable food conditions occur.
  • Matsubayashi, J., Osada, Y., Tadokoro, K., Abe, Y., Yamaguchi, A., Shirai, K., Honda, K., Yoshikawa, C., Ogawa, N.O., Ohkouchi, N., Ishikawa, N.F., Nagata, T., Miyamoto, H., Nishino, S. and Tayasu, I.
    Ecology Letters 23 5 881 - 890 2020年03月24日 [査読有り][通常論文]
  • Nishizawa, B, N. Kanna, Y. Abe, Y. Ohashi, D. Sakakibara, I. Asaji, S. Sugiyama, A. Yamaguchi, Y. Watanuki
    ICES Journal of Marine Science 77 711 - 720 2020年03月 [査読有り][通常論文]
  • Jimi, N, Yamaguchi, A, Fujiwara, Y
    Biodiversity Journal 10 4 325 - 328 2019年12月 [査読有り][通常論文]
  • 柊 萌乃, 山口 篤
    北海道大学水産科学研究彙報 69 2 83 - 91 2019年12月 [査読無し][通常論文]
  • Matsuno, K, Fujiwara, A, Hirawake, T, Yamaguchi, A
    Bulletin of the Fisheries Sciences, Hokkaido University 69 2 93 - 102 2019年12月 [査読無し][通常論文]
  • Yamaguchi, A, Ashjian, C.J, Campbell, R.G, Abe, Y
    Journal of Plankton Research 41 5 791 - 797 2019年11月 [査読有り][通常論文]
  • Fukai, Y, Matsuno, K, Fujiwara, A, Yamaguchi, A
    Polar Biology 42 10 1915 - 1922 2019年10月 [査読有り][通常論文]
  • 髙橋 卓, 森本晴之, 後藤常夫, 井口直樹, 山口 篤
    日本プランクトン学会報 66 2 60 - 71 2019年08月 [査読有り][通常論文]
  • 三島かおり, 松野孝平, 山口 篤
    北海道大学水産科学研究彙報 69 1 37 - 45 2019年08月 [査読無し][通常論文]
  • 濵 斉之, 阿部義之, 松野孝平, 山口 篤
    北海道大学水産科学研究彙報 69 1 47 - 56 2019年08月 [査読無し][通常論文]
  • Naito, A, Abe, Y, Matsuno, K, Nishizawa, B, Kanna, N, Sugiyama, S, Yamaguchi, A
    Polar Science 19 120 - 129 2019年03月 [査読有り][通常論文]
  • Amano, K, Abe, Y, Matsuno, K, Yamaguchi, A
    Polar Science 19 112 - 119 2019年03月 [査読有り][通常論文]
  • Tokuhiro, K, Abe, Y, Matsuno, K, Onodera, J, Fujiwara, A, Harada, N, Hirawake, T, Yamaguchi, A
    Polar Science 19 94 - 111 2019年03月 [査読有り][通常論文]
     
    In recent years, marine ecosystems have changed due to the drastic sea ice reduction in the Arctic Ocean, but the relationship between copepod phenology and environmental drivers is unclear. To reveal the relationship, seasonal changes in the flux (abundance of swimmers), population structure, lipid accumulation and gonad maturation of four dominant copepods (Calanus hyperboreus, Metridia longa, Paraeuchaeta glacialis and Heterorhabdus norvegicus) were studied using a sediment trap deployed at a depth of 222 m in the Pacific-Arctic sector from October 2010 to September 2013. C. hyperboreus, mostly comprising copepodid stage 6 females (C6F), exhibited several peaks in flux in spring and autumn. C. hyperboreus C6Fs were dominated by lipid-rich specimens year-round, and gonad development was observed in these samples from February to April. The M. longa flux showed no clear seasonality. Gonad maturation of M. longa C6Fs occurred from February to September. P. glacialis flux exhibited two peaks in autumn of 2011 and 2012. In contrast to the former two species, lipid-rich, mature P. glacialis C6Fs occurred year-round. H. norvegicus copepodid stage 6 males (C6Ms) also occurred throughout the year, likely because H. norvegicus has functional feeding appendages, even in C6Ms. From generalized additive models, C. hyperboreus, M. longa and P. glacialis showed relationships with daytime length and/or sea ice concentrations, but the relationship patterns were different. These findings suggest that the response (e.g., vertical migration) to the environmental parameters could vary with species and the drastic sea ice reductions may affect the copepod phenology in the Pacific-Arctic sector.
  • Maekakuchi, M, Abe, Y, Matsuno, K, Hirawake, T, Yamaguchi, A
    Bulletin of the Fisheries Sciences, Hokkaido University 68 3 43 - 49 2018年12月 [査読無し][通常論文]
  • Nakamura, Y, Somiya, R, Kanda, M, Yamaguchi, A, Tuji, A, Hori, R.S
    Journal of Eukaryotic Microbiology 65 6 923 - 927 2018年11月 [査読有り][通常論文]
     
    A phaeodarian morphotype, characterized by the feet surrounded with forked pedal spines with anchor-like structures, was collected in the subtropical North Pacific. Considering the morphological and phylogenetic uniqueness, this morphotype is described as Gazelletta kashiwaensis sp. nov. The distribution of this new species is possibly affected by the Kuroshio Current. The feeding behavior of living phaeodarians was first filmed: the present new species floated in the water column stretching "protoplasmic webs" and collected diatoms by repeating the expansion and retraction of "pseudopodium-like tentacles".
  • 山口 篤
    日本水産学会誌 84 4 744 - 747 2018年08月 [査読無し][招待有り]
  • 大洞裕貴, 宮下洋平, 小林淳希, 織田さやか, 田中邦明, 山口 篤, 今井一郎
    藻類 66 2 111 - 117 2018年07月 [査読有り][通常論文]
  • Tsukazaki, C, Ishii, K.-i, Matsuno, K, Yamaguchi, A, Imai, I
    Phycologia 57 4 440 - 452 2018年06月 [査読有り][通常論文]
  • Jose M. Landeira, Kohei Matsuno, Yuji Tanaka, Atsushi Yamaguchi
    Polar Science 16 86 - 89 2018年06月 [査読有り][通常論文]
     
    © 2018 In the Bering Sea, warming and reduction of summer sea-ice cover are driving species ranges towards the Arctic. Tanner crab, Chionoecetes bairdi, is a commercially important species in the SE Bering Sea with a northerly range margin in 62ºN. In this paper, using plankton samples collected in the Pacific sub-Arctic/Arctic sector during summer, we report for the first time the presence of larval stages (zoea II) of C. bairdi far from its northern limit of the distribution, in the south of St. Lawrence Island during 1991, and even crossing the Bering Strait into the Chukchi Sea during 1992. We suggest that the long planktonic phase (3–5 months), in combination with the oceanographic circulation, may facilitate eventual long-distance transport.
  • Hikaru Hikichi, Daichi Arima, Yoshiyuki Abe, Kohei Matsuno, Soshi Hamaoka, Seiji Katakura, Hiromi Kasai, Atsushi Yamaguchi
    Regional Studies in Marine Science 20 34 - 44 2018年04月01日 [査読有り][通常論文]
     
    To evaluate the temporal changes in zooplankton size spectra, optical plankton counter (OPC) measurements were made of high-frequency time-series zooplankton samples collected at approximately 3.5-day intervals in Mombetsu Harbour, which is located in the southern Okhotsk Sea, from January to December 2011. Based on biomasses of 47 equivalent spherical diameter (ESD) size classes binned at 0.1 mm intervals across 0.35–5 mm, the Bray–Curtis similarity index separated the zooplankton community into six groups (A–F). The occurrence of each group was separated seasonally. Thus, groups A and B were observed during the ice-covered season and summer season, respectively. During March and June, groups C–F were observed. Their occurrence varied in the short term in relation to the exchange of water masses. Groups A and C, which were observed from January to April, showed flatter normalized biomass size spectra (NBSS) slopes (−0.85 to −1.1), which indicate low productivity. In contrast, the other groups showed steeper slopes (−1.31 to −1.52) from May to December, with high productivity. Throughout the year, the frequency of highly productive groups occurred at a high level (95.2%). Although the seasonal variability in zooplankton size and productivity in Mombetsu Harbour was mainly governed by water mass exchanges, the productivity was continuously high throughout nearly all of the one-year study period.
  • Naoya Yokoi, Yoshiyuki Abe, Minoru Kitamura, Makio C. Honda, Atsushi Yamaguchi
    Deep-Sea Research Part I: Oceanographic Research Papers 133 19 - 26 2018年03月01日 [査読有り][通常論文]
     
    Seasonal changes in zooplankton swimmer (ZS) abundance, biomass and community structure were evaluated based on samples collected by moored sediment traps at a depth of 200 m in the subarctic (SA) and subtropical (ST) western North Pacific. Based on these samples, we made comparisons on two topics: 1) latitudinal (subarctic vs. subtropical) changes in ZS abundance, biomass and community and 2) quantitative differences between the ZS and particle organic carbon (POC) fluxes based on data from moored or drifting sediment traps. The results showed that the ZS flux was greater in the SA (annual mean: 311 ind. m−2 day−1 or 258 mg C m−2 day−1) than in the ST (135 ind. m−2 day−1 or 38 mg C m−2 day−1). The peak ZS flux was observed from July–August in the SA and from April–May in the ST. The dominant taxa were Copepoda and Chaetognatha in the SA and Ostracoda and Mollusca in the ST. These latitudinal differences are likely related to the dominance of large-sized Copepoda in the SA, regional differences in the timing of the spring phytoplankton bloom, and the magnitude and size structure of primary producers. The percent composition of ZS to the total C flux (= ZS+POC flux) varied by region: 85–95% in the SA and 47–75% in the ST. These differences between the ZS composition and the total C flux are most likely caused by the dominance of large-sized Copepoda (Neocalanus spp. and Eucalanus bungii) in the SA.
  • 各務彰記, 森田航也, 嶋田 宏, 山口 篤, 今井一郎
    日本プランクトン学会報 65 1 1 - 11 2018年02月 [査読有り][通常論文]
  • Danielson et
    North Pacific Research Board 2017年12月 [査読無し][通常論文]
  • Masafumi Natsuike, Rui Saito, Amane Fujiwara, Kohei Matsuno, Atsushi Yamaguchi, Naonobu Shiga, Toru Hirawake, Takashi Kikuchi, Shigeto Nishino, Ichiro Imai
    PLOS ONE 12 11 e0188565  2017年11月 [査読有り][通常論文]
     
    The eastern Bering Sea has a vast continental shelf, which contains various endangered marine mammals and large fishery resources. Recently, high numbers of toxic A. tamarense resting cysts were found in the bottom sediment surface of the eastern Bering Sea shelf, suggesting that the blooms have recently occurred. However, little is known about the presence of A. tamarense vegetative cells in the eastern Bering Sea. This study's goals were to detect the occurrence of A. tamarense vegetative cells on the eastern Bering Sea shelf and to find a relationship between environmental factors and their presence. Inter-annual field surveys were conducted to detect A. tamarense cells and environmental factors, such as nutrients, salinity, chlorophyll a, and water temperature, along a transect line on the eastern Bering Sea shelf during the summers of 2004, 2005, 2006, 2009, 2012, and 2013. A. tamarense vegetative cells were detected during every sampling year, and their quantities varied greatly from year to year. The maximum cell densities of A. tamarense observed during the summers of 2004 and 2005 were much higher than the Paralytic shellfish poisoning warning levels, which are greater than 100-1,000 cells L-1, in other subarctic areas. Lower quantities of the species occurred during the summers of 2009, 2012, and 2013. A significant positive correlation between A. tamarense quantity and water temperature and significant negative correlations between A. tamarense quantity and nutrient concentrations (of phosphate, silicate, and nitrite and nitrate) were detected in every sampling period. The surface- and bottom-water temperatures varied significantly from year to year, suggesting that water temperatures, which have been known to affect the cell growth and cyst germination of A. tamarense, might have affected the cells' quantities in the eastern Bering Sea each summer. Thus, an increase in the Bering Sea shelf's water temperature during the summer will increase the frequency and scale of toxic blooms and the toxin contamination of plankton feeders. This poses serious threats to humans and the marine ecosystem.
  • Jose M. Landeira, Kohei Matsuno, Atsushi Yamaguchi, Toru Hirawake, Takashi Kikuchi
    POLAR BIOLOGY 40 9 1805 - 1819 2017年09月 [査読有り][通常論文]
     
    Crustacean decapods are key components that structure the benthic ecosystems in the Subarctic/Arctic regions and support one of the largest fishery industries, but their larval dynamics are largely unknown. To investigate variability in decapod larvae community in this region, we analysed plankton samples collected during the summers of 2007 and 2008 along the southeastern Bering and Chukchi Seas. Distribution of adult population was studied using bottom trawling during 2008 cruise. Larvae of Pagurus spp., Hyas spp., and the commercially important Chionoecetes bairdi and Chionoecetes opilio were the most abundant species. The distribution of benthic adults linked to those of planktonic larvae and may favour recruitment near suitable habitats and the maintenance of the populations. Earlier larval stages of C. bairdi, C. opilio, and Hyas spp. were more abundant in 2008 than in 2007. The body size of C. opilio showed a significant latitudinal pattern, in which larger sizes occurred at higher latitudes in association with distinct temperature and food conditions. We argue that annual changes in abundance and developmental stage structure of planktonic larvae seemed to be related to the 1 month delay in the sampling period and are not determined by the contrasting environmental conditions observed in both years.
  • Tomiyama, K, Matsuno, K, Abe, Y, Shimada, H, Yamaguchi, A
    Bulletin of the Fisheries Sciences, Hokkaido University 67 2 25 - 34 北海道大学大学院水産科学研究院 2017年08月 [査読無し][通常論文]
     
    Inter-oceanic differences in macrozooplankton(euphausiids, amphipods, cnidarians and chaetognaths) biomass and community structure were studied in four regions(northern Japan Sea, southern Okhotsk Sea, Donan and Doto areas of North Pacific) around Hokkaido Island. Whole zooplankton biomass ranged between 25 and 315 g WM m-2 and was significantly higher in the southern Okhotsk Sea. Macrozooplankton composed 5-15% of the whole zooplankton biomass. Across all macrozooplankton taxa, the number of species varied with region : the fewest species(2-4 species) were in the southern Okhotsk Sea, followed by the northern Japan Sea(3-5 species), and the most species(4-9 species) were in the Donan and Doto areas of the North Pacific. Depth topography and thermal conditions are considered possible causes of the differences in species richness across regions. Through inter-oceanic comparison, marine ecosystem characteristics of each region were evaluated. The zooplankton community in the northern Japan Sea was characterized by a predominance of carnivorous macrozooplankton taxa(amphipods, cnidarians and chaetognaths) and fewer herbivorous taxa(euphausiids and mesozooplankton), and it was determined to be as a top-down controlled ecosystem. In contrast, in the southern Okhotsk Sea, the zooplankton community was predominated by herbivorous mesozooplankton and euphausiids, and the marine ecosystem was determined to be a bottom-up control region. In the North Pacific, zooplankton community in the Doto area was predominated by chaetognaths. The zooplankton community in the Donan area showed mixed characteristics of the Doto area and the northern Japan Sea because of the seasonal water mass exchange from these two regions.
  • Yasuhiro Takenaka, Atsushi Yamaguchi, Yasushi Shigeri
    JOURNAL OF PLANKTON RESEARCH 39 3 369 - 378 2017年05月 [査読有り][通常論文]
     
    Within the calanoid copepods, the bioluminescent species comprise 5-59% of the abundance and 10-15% of the biomass in the world's oceans. Most of the luminous species belong to the superfamily Augaptiloidea. The composition of bioluminescent species within the calanoid copepods shows latitudinal patterns; 5-25% of total calanoid copepods are found in high-latitude oceans, while 34-59% are in low-latitude oceans, reflecting a prey-predator relationship. Bioluminescent species of calanoid copepods are able to produce the light-emitting substrate coelenterazine. It is then transferred to higher predators through the food chain, and might be used for bioluminescence in other luminous organisms. A notable feature of copepod bioluminescence is the secreted-type, and its major function may be as an antipredatory response or a defensive behavior. Identification of more than 20 luciferase genes from calanoid copepods has revealed the highly conserved sequences of those genes. This leads us to the speculation that the genes for luciferase within the group of calanoid copepods have evolved independently of comparable genes outside of this group. We discuss here the ecological and biological functions of copepod bioluminescence, the significant diversity in luminous intensity, which might be evolutionarily relevant to their motility and habitat depth, and the promising future directions of bioluminescence studies.
  • Yasuhide Nakamura, Rei Somiya, Noritoshi Suzuki, Mitsuko Hidaka-Umetsu, Atsushi Yamaguchi, Dhugal J. Lindsay
    PLANKTON & BENTHOS RESEARCH 12 2 95 - 103 2017年05月 [査読有り][通常論文]
     
    Optics-based surveys for large unicellular zooplankton were carried out in five different oceanic areas. New identification criteria, in which "radiolarian-like plankton" are categorized into nine different groups, are proposed for future optics-based surveys. The autonomous visual plankton recorder (A-VPR) captured 65 images of radiolarians (three orders: Acantharia, Spumellaria and Collodaria) and 117 phaeodarians (four taxa: Aulacanthidae, Phaeosphaerida, Tuscaroridae and Coelodendridae). Colonies were observed for one radiolarian order (Collodaria) and three phaeodarian taxa (Phaeosphaerida, Tuscaroridae and Coelodendridae). The rest of the radiolarian orders (Taxopodia and Nassellaria) and the other phaeodarian taxa were not detected because of their small cell size (< ca. 400 mu m).
  • Masafumi Natsuike, Hiroshi Oikawa, Kohei Matsuno, Atsushi Yamaguchi, Ichiro Imai
    HARMFUL ALGAE 63 13 - 22 2017年03月 [査読有り][通常論文]
     
    Abundant cyst distributions of the toxic dinoflagellate Alexandrium fundyense (previous A. tamarense north American Glade) were recently observed on the north Chukchi Sea shelf and on the eastern Bering Sea shelf, suggesting that A. fundyense is both highly adapted to the local environments in the high latitude areas and might cause toxin contamination of plankton feeders. However, little is known about the physiological characteristics and toxin profiles of A. fundyense in these areas, which are characterized by low water temperatures, weak sunlight, and more or less permanent ice cover during winter. To clarify the physiological characteristics of A. fundyense, the effects of water temperature and light intensity on the vegetative growth and toxin profiles of this species were examined using A. fundyense strains isolated from one sediment sample collected from each area. Using the same sediments samples, seasonal changes of the cyst germination in different water temperatures were investigated. Vegetative cells grew at temperatures as low as 5 degrees C and survived at 1 degrees C under relatively low light intensity. They also grew at moderate water temperatures (10-15 degrees C). Their cysts could germinate at low temperatures (1 degrees C) and have an endogenous dormancy period from late summer to early spring, and warmer water temperatures (5-15 degrees C) increased germination success. These physiological characteristics suggest that A. fundyense in the Chukchi Sea and eastern Bering Sea is adapted to the environments of high latitude areas. In addition, the results suggest that in the study areas A. fundyense has the potential to germinate and grow when water temperatures increase. Cellular toxin amounts of A. fundyense strains from the eastern Bering Sea and Chukchi Sea were ranged from 7.2 to 38.2 fmol cell(-1). These toxin amounts are comparable with A. fundyense strains isolated from other areas where PSP toxin contamination of bivalves occurs. The dominant toxin of the strains isolated from the Chukchi Sea was saxitoxin, while mostA.fundyense strains from the eastern Bering Sea are dominated by the C2 toxin. Toxin profiles similar to those detected in Chukchi Sea have not been reported by any previous research. The dominance of a highly toxic PST variant in Chukchi A. fundyense suggests that presence of the species at low cell concentrations may cause toxin contamination of predators. This study revealed that abundant A. fundyense cysts deposited on the eastern Bering Sea and Chukchi Sea shelves potentially germinate and grow with PSP toxin contents in the local environments. In conclusion, a high risk of PSP occurrences exists on the eastern Bering Sea and Chukchi Sea shelves. (C) 2017 Elsevier B.V. All rights reserved.
  • Yuichiro Kumamoto, Michio Aoyama, Yasunori Hamajima, Hisao Nagai, Takeyasu Yamagata, Yoshimi Kawai, Eitarou Oka, Atsushi Yamaguchi, Keiri Imai, Akihiko Murata
    JOURNAL OF RADIOANALYTICAL AND NUCLEAR CHEMISTRY 311 2 1209 - 1217 2017年02月 [査読有り][通常論文]
     
    In 2014, we measured activity concentration of radiocesium in the western North Pacific Ocean. In the north of Kuroshio Front high activity concentration of Fukushima-derived radiocesium in surface mixed layer in 2012 had been transported eastward by 2014. In the south of the front we found a radiocesium subsurface maximum in 200-600 m depth, which was similar to that observed in 2012. The subsurface maximum spread southward from 18A degrees N to 15A degrees N between 2012 and 2014, which suggests spreading of Fukushima-derived radiocesium into the whole western subtropical area by 2014 due to formation and subduction of the subtropical mode water.
  • Asami Nakamura, Kohei Matsuno, Yoshiyuki Abe, Hiroshi Shimada, Atsushi Yamaguchi
    ZOOLOGICAL STUDIES 56 13 - 13 2017年 [査読有り][通常論文]
     
    While length-weight (L-W) regressions for warm-water zooplankton taxa from the waters neighbouring Japan already exist, they are still missing for comparable cold-water species. In this study, the L-W regressions of 41 species belonging to 12 taxa that are dominant in the Oyashio region were reported. The body length and volume of zooplankton were measured with an image-analysis system, and the effects of lipid accumulation in Copepoda on their mass and chemical composition were quantified. The L-W regressions had a high coefficient of determination (mean r(2) = 0.886). For the chemical composition, the water composition ranged from 69.8 to 95.2% wet mass (WM), carbon (C) composition from 3.8 to 60.8% dry mass (DM) and nitrogen (N) composition from 1.0 to 10.1% DM. Taxon-specific differences in the chemical composition were marked for the gelatinous taxa (Appendicularia, Cnidaria, Salpida), which also had high water and low C composition. Because C is an index of lipids, high water compositions together with low lipid compositions are considered to be characteristics of the gelatinous taxa. The most significant effects of lipid accumulation in the Copepoda are changes in DM and C. Within the same developmental stage, the DM and C compositions of the full lipid-containing specimens showed 495% and 741% increases, respectively, over those of the low lipid-containing specimens. These differences exceeded the changes after moulting (78.1%) for general copepod species. Thus, lipid accumulation should be evaluated for the accurate mass estimation of boreal Copepoda by image analysis.
  • Dhugal J. Lindsay, Jun Nishikawa, Keisuke Sunahara, Yoshihiro Fujiwara, Atsushi Yamaguchi
    Plankton and Benthos Research 12 1 66 - 70 2017年 [査読有り][通常論文]
     
    © The Plankton Society of Japan. A doliolid species belonging to the genus Paradoliopsis was photographed by an Autonomous Visual Plankton Recorder (AVPR) off the eastern seaboard of Japan in October 2014 at 493–512 m depth. Two Paradoliopsis gonozooids were also captured on the video record of the ROV Crambon at 372–373 m depth during the same cruise. This is the first record of this genus from the Pacific Ocean, and although it resembles the sole described species in this genus, P. harbisoni Godeaux, 1996, some aspects of its morphology suggest it may be an as-yet-undescribed species.
  • Masafumi Natsuike, Kohei Matsuno, Toru Hirawake, Atsushi Yamaguchi, Shigeto Nishino, Ichiro Imai
    HARMFUL ALGAE 61 80 - 86 2017年01月 [査読有り][通常論文]
     
    A high abundance of resting cysts of the toxic dinoflagellate Alexandrium tamarense was recently reported in the vast continental shelf of the Chukchi Sea in the Arctic Ocean, suggesting that the species is widespread in the shelf. Nevertheless, little is known about the occurrence of A. tamarense vegetative cells in the water column of the arctic. Sea ice reduction and the inflow of Pacific summer water (PSW) through the Bering Strait have recently increased owing to warming in the shelf. To determine the spatial and temporal distributions of A. tamarense in the Chukchi Sea shelf and their relationship to the inflow of PSW, field samplings were conducted in the Chukchi Sea and north Bering Sea shelves three times during the summer of 2013 from July to October. Vegetative cells of A. tamarense was detected in both shelves at all sampling periods with a maximum density of 3.55 x 10(3) cells L-1. This species was also observed at the station at 73 degrees N, indicating the northernmost record of this species to date. The center of the A. tamarense distribution was between the north Bering and south Chukchi Sea shelf during the first collection period, and spread to the north Chukchi Sea shelf during the second and third collection periods. The species occurrences were mainly observed at stations affected by the PSW, especially Bering shelf water. Water structure of PSW was characterized by warmer surface and bottom water temperatures, and increased temperatures may have promoted the cell growth and cyst germination of A. tamarense. Therefore, it is suggested that an increase in the PSW inflow owing to warming promotes toxic A. tamarense occurrences on the Chukchi Sea shelf. (C) 2016 Elsevier B.V. All rights reserved.
  • Bungo Nishizawa, Kohei Matsuno, Elizabeth A. Labunski, Kathy J. Kuletz, Atsushi Yamaguchi, Yutaka Watanuki
    BIOGEOSCIENCES 14 1 203 - 214 2017年01月 [査読有り][通常論文]
     
    The short-tailed shearwater (Ardenna tenuirostris) is one of the abundant marine top predators in the Pacific; this seabird spends its non-breeding period in the northern North Pacific during May-October and many visit the southern Chukchi Sea in August-September. We examined potential factors affecting this seasonal pattern of distribution by counting short-tailed shearwaters from boats. Their main prey, krill, was sampled by net tows in the southeastern Bering Sea/Aleutian Islands and in the Bering Strait/southern Chukchi Sea. Short-tailed shearwaters were mainly distributed in the southeastern Bering Sea/Aleutian Islands (60 +/- 473 birds km(-2)) in July 2013, and in the Bering Strait/southern Chukchi Sea (19 +/- 91 birds km(-2)) in September 2012. In the Bering Strait/southern Chukchi Sea, krill size was greater in September 2012 (9.6 +/- 5.0 mm in total length) than in July 2013 (1.9 +/- 1.2 mm). Within the Bering Strait/southern Chukchi Sea in September 2012, short-tailed shearwaters occurred more frequently in cells (50 +/- 50 km) where large-sized krill were more abundant. These findings, and information previously collected in other studies, suggest that the seasonal northward movement of short-tailed shearwaters might be associated with the seasonal increase in krill size in the Bering Strait/southern Chukchi Sea. We could not, however, rule out the possibility that large interannual variation in krill abundance might influence the seasonal distribution of shearwaters. This study highlights the importance of krill, which is advected from the Pacific, as an important prey of top predators in the Arctic marine ecosystem.
  • Yamaguchi, A, Matsuno, K, Abe, Y, Arima, D, Imai, I
    Progress in Oceanography 150 13 - 19 2017年01月 [査読有り][通常論文]
     
    A total of 100 mesozooplankton samples collected with NORPAC nets from a 0 to 150-m depth at latitudinal stations (35-44 degrees N) along 155 degrees E each May from 2002 through 2011 were analyzed. The mesozooplankton abundance at each station varied from 39 to 1106 ind. m(-3). The mesozooplankton biomass was consistently higher (80-100 mg DM m(-3)) in the transition domain (40-42 degrees N) than the biomass in the other domains. An empirical metabolic rate-based carbon budget model indicated that production of mesozooplankton suspension feeders was highest (120-175 mg C m(-2) d(-1)) in the transition domain. A comparison between the production of the mesozooplankton suspension feeders and the food requirement of mesozooplankton carnivores indicated that the latter was well fulfilled by the former in the subarctic and transition domains. However, the food requirement of the mesozooplankton carnivores was near equal to or exceeded the production of mesozooplankton suspension feeders in the subtropical domain. As an annual event, the feeding migration of epipelagic fish to the transition and subarctic domains in summer may be interpreted by their utilization of the excess secondary production (production of mesozooplankton suspension feeders). (C) 2015 Elsevier Ltd. All rights reserved.
  • Kohei Matsuno, Yoshiyuki Abe, Atsushi Yamaguchi, Takashi Kikuchi
    POLAR SCIENCE 10 4 503 - 510 2016年12月 [査読有り][通常論文]
     
    In the Arctic Ocean, Calanus glacialis is the most dominant species in zooplankton biomass. While important, little information is available concerning the factors controlling their population. In this study, we evaluated regional patterns and environmental factors controlling the population structure of C. glacialis in the western Arctic Ocean in summer months (July-October) in 1991, 1992, 2007, 2008, 2010, 2012, 2013 and 2014. To evaluate regional patterns, environmental parameters (temperature, salinity and chlorophyll a) and C. glacialis population parameters (abundance, biomass, mean copepodid stage and lipid accumulation) were divided into three latitudinal regions. In all three regions from July to October, chlorophyll a decreased, while the mean copepodid stage increased. These results suggest phytoplankton blooms occurred early in the sampling period, and C. glacialis grew during the period. From Structural Equation Model (SEM) analysis, the controlling factors on the C. glacialis population were evaluated. The results of the SEM analysis indicated positive correlations between abundance and biomass; Julian day and mean copepodid stage; and temperature and mean copepodid stage. Additionally, a negative correlation between abundance and mean copepodid stage was observed. (C) 2016 Elsevier B.V. and NIPR. All rights reserved.
  • Yoshiyuki Abe, Hiroomi Miyamoto, Rui Saito, Kohei Matsuno, Atsushi Yamaguchi, Ichiro Imai
    REGIONAL STUDIES IN MARINE SCIENCE 8 122 - 132 2016年11月 [査読有り][通常論文]
     
    In the Oyashio region, the dominant water masses are switched at the surface layer within a short period during spring. Simultaneously, a large phytoplankton bloom is known to occur at the surface layer, and nearly half of the annual primary production is concentrated during spring. These drastic changes in the water mass and food condition are expected to strongly affect the macrozooplankton population dynamics. However, their effects on the chaetognath population remain unknown. To evaluate the effects of the water mass exchange and spring phytoplankton bloom, we analysed short-term changes in the population structure, growth rate, gut contents and predation impact of the three dominant chaetognaths (Eukrohnia hamata, Parasagitta elegansand Pseudosagitta scrippsae) in the Oyashio region during March-April 2007. Eleven samples were collected by a 0-200 m oblique tow of a Bongo net at night during 9 March to 30 April, 2007. The effects of the water mass exchange were significant for all three chaetognath species. During the sampling period, significant growth was observed for the two dominant species (E. hamata and P. elegans). The daily growth rate was 39-50 mu m day(-1) for E. hamata and 42-101 mu m day(-1) for P. elegans. The mean predation impact of P. elegans at 0-200 m was 0.194 no. prey consumed m(-3) day(-1) and that of P. scrippsae was 0.028 no. prey consumed m(-3) day(-1). These values corresponded with 0-0.097% (P. elegans) or 0-0.043% (P. scrippsae) of the total zooplankton abundance during the spring. (C) 2016 Published by Elsevier B.V.
  • Kohei Matsuno, Jose M. Landeira Sanchez, Atsushi Yamaguchi, Toru Hirawake, Takashi Kikuchi
    POLAR SCIENCE 10 3 335 - 345 2016年09月 [査読有り][通常論文]
     
    From July to August 2007 and June to July 2008, the horizontal/geographical changes in the zooplankton community in the Bering and Chukchi Seas were studied. The geographical patterns, which were common for these two years, were observed for salinity, chlorophyll a (Chl. a), zooplankton chaetognaths, hydrozoans and the whole zooplankton community. Among them, the patterns of salinity and Chl. a were related with the horizontal distribution of the water masses. The distributions of the two carnivorous taxa were correlated with their prey (copepods or barnacle larvae). The analysis of the structural equation model (SEM) revealed that the horizontal distribution of the zooplankton abundance and biomass were governed by the different taxa. Thus, the zooplankton abundance was governed by the numerically dominant but smaller-bodied taxa, such as the barnacle larvae and copepod Pseudocalanus spp., while the zooplankton biomass was determined by the large-bodied copepods, such as Calanus glacialis/marshallae and Eucalanus bungii. (C) 2016 Elsevier B.V. and NIPR.
  • Matsuno, K, Yamaguchi, A, Fujiwara, A, Onodera, J, Watanabe. E, Harada, N, Kikuchi, T
    Bulletin of the Fisheries Sciences, Hokkaido University 66 2 77 - 85 北海道大学大学院水産科学研究院 2016年08月10日 [査読無し][通常論文]
     
    In the western Arctic Ocean, the long sea ice coverage period prevents year-round seasonal zooplankton sampling by ordinary ship-board observation. To overcome these problems, the analysis of zooplankton swimmers in samples collected by a year-round moored sediment trap may be a powerful tool. In this study, we studied seasonal changes in zooplankton swimmer community and fecal pellets collected by a sediment trap moored at fixed depths(180-260m) of the Northwind Abyssal Plain in the western Arctic Ocean from October 2010 to September 2012. The fecal pellets were separated into four types : oval, cylinder, spherical and brown-colored pellets. The occurrence of brown-colored pellets was limited to the open water period(July-August) and reached 80% of the total at that time. Ship-board experiments showed that the brown-colored fecal pellets were egested by amphipods(Themisto libellula). The high occurrence of brown-colored fecal pellets during the open water period might be a reflection of the massive feeding activity of amphipods. Zooplankton swimmer flux ranged from 35-739 ind m-2 day-1, and poecilostomatoid copepods were the most abundant(accounted for 69% of the annual mean). Seasonally, barnacle and bivalve larvae were abundant during August-September and August-November, respectively. These meroplanktionic larvae were considered to be transported by current flow from the southern continental shelf, whereas they were absent from summer to autumn 2012. The annual changes in meroplanktonic larvae occurrence would be a reflection of the annual changes in water mass formation at the upper layer of the sediment trap moored station.
  • Hiroko Sasaki, Kohei Matsuno, Amane Fujiwara, Misaki Onuka, Atsushi Yamaguchi, Hiromichi Ueno, Yutaka Watanuki, Takashi Kikuchi
    BIOGEOSCIENCES 13 15 4555 - 4567 2016年08月 [査読有り][通常論文]
     
    The advection of warm Pacific water and the reduction in sea ice in the western Arctic Ocean may influence the abundance and distribution of copepods, a key component of food webs. To quantify the factors affecting the abundance of copepods in the northern Bering and Chukchi seas, we constructed habitat models explaining the spatial patterns of large and small Arctic and Pacific copepods separately. Copepods were sampled using NORPAC (North Pacific Standard) nets. The structures of water masses indexed by principle component analysis scores, satellite-derived timing of sea ice retreat, bottom depth and chlorophyll a concentration were integrated into generalized additive models as explanatory variables. The adequate models for all copepods exhibited clear continuous relationships between the abundance of copepods and the indexed water masses. Large Arctic copepods were abundant at stations where the bottom layer was saline; however they were scarce at stations where warm fresh water formed the upper layer. Small Arctic copepods were abundant at stations where the upper layer was warm and saline and the bottom layer was cold and highly saline. In contrast, Pacific copepods were abundant at stations where the Pacific-origin water mass was predominant (i.e. a warm, saline upper layer and saline and a highly saline bottom layer). All copepod groups showed a positive relationship with early sea ice retreat. Early sea ice retreat has been reported to initiate spring blooms in open water, allowing copepods to utilize more food while maintaining their high activity in warm water without sea ice and cold water. This finding indicates that early sea ice retreat has positive effects on the abundance of all copepod groups in the northern Bering and Chukchi seas, suggesting a change from a pelagic-benthic-type ecosystem to a pelagic-pelagic type.
  • 小島千里, 宮下洋平, 萩原 匠, 山口 篤, 今井一郎
    北海道大学水産科学研究彙報 66 1 19 - 28 北海道大学大学院水産科学研究院 2016年03月10日 [査読無し][通常論文]
     
    Toxic blooms of cyanobacteria have negative impacts on fresh water ecosystems, and there is an urgent need to develop strategies to control those blooms. Algicidal bacteria that kill noxious species of cyanobacteria are expected as tools for mitigating impacts of the toxic cyanobacterial blooms. This study carried out to search algicidal bacteria against toxic cyanobacteria from biofilm on reeds and water samples in reed communities in Ohnuma Quasi-National Park and evaluated for control ability of cyanobacterial bloom by bacteria from reeds. Bacteria were isolated from the biofilm on reed and water samples, and the algicidal ability was examined using Microcystis aeruginosa by co-culture experiments. Algicidal bacteria were detected in high densities(order of 10⁵-10⁶ CFU g⁻¹ wet reed weight) from the biofilm of reeds including artificially planted reeds. Water samples from reed communities also contained more algicidal bacteria than those samples from no reed communities. The results suggested a possibility that reeds supply algicidal bacteria to adjacent water and reed communities have high potential ability to control toxic cyanobacterial blooms via bacteria possessing algicidal and groth-inhibiting activities.
  • 松本健太郎, 有馬大地, 松野孝平, 山﨑康裕, 大西広二, 大木淳之, 平譯 享, 山口 篤, 今井一郎
    北海道大学水産科学研究彙報 66 1 29 - 38 北海道大学大学院水産科学研究院 2016年03月 [査読無し][通常論文]
     
    The spring phytoplankton community in the western North Pacific is characterized by large variability in both the horizontal and verical dimensions. To evaluate this variability, phytoplankton communitiesat 39°30'N-44°00'N along 155°E were investigated in situ using a multi-excitation fluorometer during May 2014. The sea surface chlorophyll a(Chi. a) level was high and composed mainly of diatoms near 43°30'N-42'N, while it was low and composed of dinoflagellates south of 40°N. Based on seven fixed-station investigations, the phytoplanklton communities were classified into 4 types : a low Chl. a level before bloom (44°N), massive diatom bloom(42°N-43°N), low Chl. a level with dinoflagellates(40°N-41°N) and lowest Chl.a(at the southernmost station at 39°30'N). These phytoplankton communities corresponded with the formation of a water mass separating the Subartctic front(SAF) and Subarctic boundary(SAB). Multi-excitation fluorometry data showed a high correlation with Chl. a measurements obtained via Thrmo-salinometer and biovolume microscopic analyses(r²=0.67-0.97,p<0.05). Thus, we concluded that a multi-excitation fluorometer can be applied for the evaluation of detailed spatial and temporal changes in the phytoplankton community at various locations.
  • Daichi Arima, Atsushi Yamaguchi, Takahiro Nobetsu, Ichiro Imai
    CRUSTACEANA 89 2 151 - 161 2016年 [査読有り][通常論文]
     
    In the Okhotsk Sea, the calanoid copepod Metridia okhotensis Brodsky, 1950 is the dominant component of zooplankton, accounting for 61% of the annual mean total pelagic copepods. Although this organism is important, little ecological information is available for M. okhotensis in the Okhotsk Sea because of the ice cover during winter, which prevents the collection of seasonal samples in this region. Here, we report the seasonal changes in the population structure, sex ratio and female gonad maturation of M. okhotensis. The data are from samples collected using water pumped from a depth of 350 m off Rausu Harbour in the Okhotsk Sea at 2-week intervals over a 2.5-year period. Due to the mesh size of the strainer (420 mu m), M. okhotensis was collected from C3 to adults. The sex ratio of C5 (female : male) was approximately 1 : 1 throughout the year. In contrast, the sex ratio of C6 (adult) showed a clear seasonality, with males (C6M) occurring only from December to May and females (C6F) dominating during the other seasons. The gonad maturation of C6F was scored using five categories, and their composition also showed clear seasonality. From January to April, gonads developed rapidly from stage I (immature) to V (spawning). During the other seasons, the majority of C6F had immature gonads. Based on these data, we conclude that this species likely has a diapause phase for C6F, with immature gonads, and C5M from June to November. Moulting from C5M to C6M began in December. Accompanying the occurrence of C6M, C6F were fertilized from December to January. C6F underwent gonad maturation from January to April and performed primary reproduction from April to May. Thereafter, M. okhotensis entered diapause from June to November.
  • Naoya Yokoi, Kohei Matsuno, Mutsuo Ichinomiya, Atsushi Yamaguchi, Shigeto Nishino, Jonaotaro Onodera, Jun Inoue, Takashi Kikuchi
    BIOGEOSCIENCES 13 4 913 - 923 2016年 [査読有り][通常論文]
     
    Recent studies indicate an increase in atmospheric turbulence in the Chukchi Sea due to the recent drastic sea-ice reduction during summer months. The importance of the effects of this atmospheric turbulence on the marine ecosystem in this region, however, is not fully understood. To evaluate the effects of atmospheric turbulence on the marine ecosystem, high-frequency sampling (daily) from five layers of the microplankton community between 0 and 30 m at a fixed station in the Chukchi Sea from 10 through 25 September 2013 was conducted. During the study period, a strong wind event (SWE) was observed on 18 and 19 September. The abundance of microplankton was 2.6 to 17.6 cells mL(-1), with a maximum abundance being reported at 20 m on 22 September, while diatoms were the most dominant taxa throughout the study period. The abundance of diatoms, dinoflagellates and ciliates ranged between 1.6 and 14.1, 0.5 and 2.4 and 0.1 and 2.8 cells mL(-1), respectively. Diatoms belonging to 7 genera consisting of 35 species (Cylindrotheca closterium and Leptocylindrus danicus were dominant), dinoflagellates belonging to 7 genera consisting of 25 species (Prorocentrum balticum and Gymnodinium spp. were dominant) and ciliates belonging to 7 genera consisting of 8 species (Strobilidium spp. and Strombidium spp. were dominant) were identified. Within the microplankton species, there were 11 species with abundances that increased after the SWE, while there was no species with an abundance that decreased following the SWE. It is conjectured that atmospheric turbulences, such as that of an SWE, may supply sufficient nutrients to the surface layer that subsequently enhance the small bloom under the weak stratification of the Chukchi Sea Shelf during the autumn months. After the bloom, the dominant diatom community then shifts from centric-dominated to one where centric/pennate are more equal in abundance.
  • Yoshiyuki Abe, Yuichiro Yamada, Rui Saito, Kohei Matsuno, Atsushi Yamaguchi, Kosei Komatsu, Ichiro Imai
    REGIONAL STUDIES IN MARINE SCIENCE 3 154 - 162 2016年01月 [査読有り][通常論文]
     
    Short-term changes in the population structure of dominant amphipods in the Oyashio region during the spring bloom were studied and discussed from the perspective of the effect of water mass change and the utilization of a phytoplankton bloom. Throughout the sampling period, amphipods belonging to 9 genera and 13 species were found. Among them, three amphipods (Cyphocaris challengeri, Primno abyssalis and Themisto pacifica) accounted for 89% of the total amphipod abundance and 92% of the biomass. For C. challengeri, the compositions of egg-and juvenile-carrying specimens within mature females were increased through April; juveniles exhibited a drastic increase in late April. These facts suggest that C. challengeri primarily achieved reproduction during the spring phytoplankton bloom. For P. abyssalis, growth of the mean body length was observed for each juvenile cohort. Thus, P. abyssalis achieved juvenile growth during the spring phytoplankton bloom. For T. pacifica, the compositions of egg-and juvenile-carrying females increased through April. These facts suggest that T. pacifica achieved maturation during the spring phytoplankton bloom. The effect of the water mass exchange on the amphipod population was more moderate than that observed on the other macrozooplankton taxa. This finding may be a result of a strong diel vertical migration behavior, which functions to maintain the population position. The species-specific differences in the amphipods in the utilization of spring phytoplankton may be related to the species-specific life cycle timing (phenology) in this region. (C) 2015 Elsevier B.V. All rights reserved.
  • Daichi Arima, Atsushi Yamaguchi, Takahiro Nobetsu, Ichiro Imai
    REGIONAL STUDIES IN MARINE SCIENCE 3 18 - 24 2016年01月 [査読有り][通常論文]
     
    The Okhotsk Sea is the southernmost seasonally ice-covered ocean in the Northern Hemisphere. Because of the ice coverage during winter, seasonal monitoring of zooplankton is difficult by ordinary ship-board observation. To overcome this issue, zooplankton monitoring of samples collected by deep-ocean water pumping may be useful. In this study, we evaluated seasonal changes in the zooplankton community based on the samples collected by deep-ocean water pumped from a 350-m depth off of Rausu Harbor in the southern Okhotsk Sea at 2.5-day intervals over two and a half years. Zooplankton abundance and biomass ranged from 20-550 inds. m(-3) and 6-902 mg WM m(-3), respectively. Both parameters showed similar seasonal changes throughout the study period. Copepods were the most dominant taxa throughout the year and accounted for 90% and 76% of the annual mean zooplankton abundance and biomass, respectively. A total of 20 genera and 33 copepod species were observed. Metridia okhotensis and M. pacifica accounted for 61% and 12% of the annual mean copepod abundance, respectively. In general, the abundance and biomass of zooplankton collected by pumped-up deep-ocean water were lower than they were in the epipelagic layer (both characteristics of the former corresponded to approximately 60% of the latter). The combined effects of low zooplankton density at the deep layer (350 m) and the low filtering rate of deep-water pumping are considered to be a possible cause of the low zooplankton abundance and biomass in the pumped-up deep-ocean water. For the zooplankton samples from pumped-up deep-ocean water, there was a high abundance of benthopelagic mysids and copepods (Xanthocalanus spp.). Because the water inlet of the deep-ocean water pumping is located near the sea bottom, the collected samples may be useful for the evaluation of seasonal changes in the population structure of the less-studied benthopelagic species. (C) 2015 Elsevier B.V. All rights reserved.
  • Kohei Matsuno, Atsushi Yamaguchi, Amane Fujiwara, Jonaotaro Onodera, Eiji Watanabe, Naomi Harada, Takashi Kikuchi
    JOURNAL OF NATURAL HISTORY 49 45-48 2711 - 2726 2015年10月 [査読有り][通常論文]
     
    Winter ice cover of the Arctic Ocean makes year-round zooplankton sampling by plankton net a difficult task. Therefore, the collection of copepods with a sediment trap can be a powerful tool. In the present study, we analysed the seasonal changes in the population structures of five dominant planktonic copepods (Oncaea parila, Calanus hyperboreus, Metridia longa, Paraeuchaeta glacialis and Heterorhabdus norvegicus), which were collected using a sediment trap rotated at 10-15day intervals moored at 184-260m in the Northwind Abyssal Plain (75 degrees 00N, 162 degrees 00W) of the western Arctic Ocean from October 2010 to September 2012. Oncaea parila C6F with egg sacs occurred throughout the year, and the total abundance and composition of early copepodid stages (C1-C3) had two peaks each year. Calanus hyperboreus was dominated by C6F throughout the year, and their maturation was observed during February to May. Metridia longa C6F had a clear seasonality in lipid accumulation and gonad maturation: high lipid accumulation was observed from October to February, whereas gonad maturation occurred from March to September. Paraeuchaeta glacialis C6F also showed seasonality in lipid accumulation and gonad maturation, although their seasonal patterns varied from those of M. longa: high lipid individuals were abundant from February to April and mature individuals dominated from October to November. Heterorhabdus norvegicus showed seasonal changes in population structure as well: C1, C5, and C6M dominated from April to May, November to February and August to October, respectively. The life cycle patterns of these species are compared with those reported from other areas. While the results obtained by a sediment trap are inevitably subject to collection bias (i.e. passive collection at a fixed depth), a sediment trap should be considered as a powerful tool for the evaluation of the life cycle of planktonic copepods, especially in ice-covered oceans.
  • Atsushi Yamaguchi
    JOURNAL OF NATURAL HISTORY 49 45-48 2743 - 2757 2015年10月 [査読有り][通常論文]
     
    Several aspects of the ecology of planktonic copepods (vertical distribution, abundance, community structure, population structure and body size) were evaluated and compared between communities in the autumn, in the Okhotsk Sea and the adjacent Oyashio region in the western North Pacific. Vertically, copepods were concentrated primarily at depths of 250 to 500m in the Okhotsk Sea but near the surface in the Oyashio region. The abundances of most of the copepods were greater in the Oyashio region with the exception of Metridia okhotensis, which showed significantly greater abundance in the Okhotsk Sea (30 times greater) and dominated the copepod community, accounting for approximately 70% of total copepod abundance. The population structure of the dominant copepods in the Okhotsk Sea was dominated by late copepod stages, suggesting that these copepods were in the resting phase. The prosome lengths of most of the copepods were larger in the Okhotsk Sea than in the Oyashio region and the larger body size is probably due to the lower habitat temperatures. The special ecological characteristics of planktonic copepods in the Okhotsk Sea are possibly related to the development of a strong pycnocline in the Okhotsk Sea. The consequences of differences in copepod communities between regions were discussed from the viewpoints of life cycle timing and the scale of active vertical flux.
  • Eiji Watanabe, Jonaotaro Onodera, Naomi Harada, Makio C. Honda, Katsunori Kimoto, Takashi Kikuchi, Shigeto Nishino, Kohei Matsuno, Atsushi Yamaguchi, Akio Ishida, Michio J. Kishi
    NATURE COMMUNICATIONS 6 8441  2015年09月 [査読有り][通常論文]
  • Elizaveta A. Ershova, Russell R. Hopcroft, Ksenia N. Kosobokova, Kohei Matsuno, R. John Nelson, Atsushi Yamaguchi, Lisa B. Eisner
    OCEANOGRAPHY 28 3 100 - 115 2015年09月 [査読有り][通常論文]
     
    The Chukchi Sea pelagic ecosystem, which is finely tuned to the region's seasonal ice formation and retreat, has been undergoing dramatic oceanographic change related to shifting sea ice cover and increasing temperatures over the last decades. We examine historical data sets on zooplankton communities in the central Chukchi Sea during the time period 1946 to 2012. Analysis is confounded by differences between years in terms of spatial coverage, seasonal variability, and methodology; nonetheless, trends remain detectable when a sufficient number of study years is compiled. In addition to high levels of interannual variability, we demonstrate that there have been significant increases in zooplankton biomass and abundance in recent years compared to historical studies, along with shifting distribution ranges for several key species. This signal is most pronounced for the copepods, particularly Calanus glacialis, which appears to be indirectly benefiting from warming of the region. While summer zooplankton communities of the Chukchi Sea have been primarily Bering-Pacific in character for as long as records exist, continuing warming and ice loss are increasing the influence of Bering-Pacific fauna within the Chukchi region.
  • Yasuhide Nakamura, Ichiro Imai, Atsushi Yamaguchi, Akihiro Tuji, Fabrice Not, Noritoshi Suzuki
    PROTIST 166 3 363 - 373 2015年07月 [査読有り][通常論文]
     
    Phaeodarians are a group of widely distributed marine cercozoans. These plankton organisms can exhibit a large biomass in the environment and are supposed to play an important role in marine ecosystems and in material cycles in the ocean. Accurate knowledge of phaeodarian classification is thus necessary to better understand marine biology, however, phylogenetic information on Phaeodaria is limited. The present study analyzed 18S rDNA sequences encompassing all existing phaeodarian orders, to clarify their phylogenetic relationships and improve their taxonomic classification. The monophyly of Phaeodaria was confirmed and strongly supported by phylogenetic analysis with a larger data set than in previous studies. The phaeodarian clade contained 11 subclades which generally did not correspond to the families and orders of the current classification system. Two families (Challengeriidae and Aulosphaeridae) and two orders (Phaeogromida and Phaeocalpida) are possibly polyphyletic or paraphyletic, and consequently the classification needs to be revised at both the family and order levels by integrative taxonomy approaches. Two morphological criteria, 1) the scleracoma type and 2) its surface structure, could be useful markers at the family level. (C) 2015 Elsevier GmbH. All rights reserved.
  • Kohei Matsuno, Atsushi Yamaguchi, Toru Hirawake, Shigeto Nishino, Jun Inoue, Takashi Kikuchi
    POLAR BIOLOGY 38 7 1075 - 1079 2015年07月 [査読有り][通常論文]
     
    The species composition of Arctic zooplankton differs greatly from that of the zooplankton of the North Pacific and Bering Sea. Particularly with greater warming from sea-ice retreat, the reproduction of North Pacific species transported into the Chukchi Sea and beyond may lead to changes in the Arctic pelagic ecosystem. We report the egg production and hatching of the Pacific copepod Neocalanus flemingeri in the Chukchi Sea based on shipboard experiments performed in September 2013. The reproductive capability of N. flemingeri observed in the Chukchi Sea resembled that reported in the Pacific, with the exception of a lower hatching success. Only 7.5 % of N. flemingeri eggs hatched compared with 93 % in Pacific experiments. Low hatching success is considered to be caused by failures of fertilization. The potential recruitment number for N. flemingeri suggests that it is unlikely to establish expatriate Arctic populations in the near future.
  • Yasuhiro Takenaka, Atsushi Yamaguchi, Yasushi Shigeri
    Seikagaku. The Journal of Japanese Biochemical Society 87 1 138 - 43 2015年02月
  • 夏池真史, 金森 誠, 馬場勝寿, 山口 篤, 今井一郎
    日本プランクトン学会報 62 1 1 - 7 日本プランクトン学会 2015年02月01日 [査読有り][通常論文]
     
    Heterosigma akashiwo (Hada) Hadaはラフィド藻綱(Class Raphidophyceae)の1種であり，2本の亜等長の鞭毛を持つ細胞長8-25μm，幅6-15μM程度，楕円形でやや扁平な植物プランクトンである。本種は赤潮を形成して養殖魚類の斃死を引き起こす有害赤潮形成種である。本種赤潮による漁業被害として，日本では養殖ブリ類(ハマチ，カンパチ，ヒラマサ)，マダイ，シマアジ(本城1997，折田ほか1999，今井2013)，外国では亜寒帯に位置するカナダ(Tayler 1990)や温帯に位置するニュージーランドなどで(Chang et al. 1990)で養殖サケ類の斃死が報告されている。本種はわが国において北海道小樽から沖縄県糸満までの亜寒帯から亜熱帯で出現が確認されており(原1990)，三陸沿岸から東京湾，伊勢湾，瀬戸内海や四国および九州沿岸域などの本州以南の太平洋側の沿岸域を中心に赤潮の形成が報告されている(本城1997，西谷ほか2013)。本種の北海道における出現は，小樽，函館湾および噴火湾において報告されている程度であり(原1990，本城1997，夏池ほか2012)，本種の北海道における生態はほとんど明らかにされていない。そこで，本研究では亜寒帯に位置する北海道南部の噴火湾内の2定点において2年4ヶ月にわたる定期調査を行い，北日本では初めて本種の周年に亘る出現状況および本種出現と環境条件との関係を調べたので報告する。
  • Short-term changes in a microplankton community in the Chukchi Sea during autumn: consequences of a strong wind event.
    Yokoi N, Matsuno K, Ichinomiya M, Yamaguchi A, Nishino S, Onodera J, Inoue J, Kikuchi T
    Biogeosciences 12 8789 - 8817 2015年 [査読有り][通常論文]
  • Daichi Arima, Kohei Matsuno, Atsushi Yamaguchi, Takahiro Nobetsu, Ichiro Imai
    CRUSTACEANA 88 12-14 1307 - 1321 2015年 [査読有り][通常論文]
     
    The seasonal and inter-annual changes in the asymmetry of female insemination and the male leg 5 of the planktonic calanoid copepods Metridia okhotensis and M. pacifica were investigated in the Okhotsk Sea. An inter-species comparison of both parameters was also carried out on seven Metridia species collected from oceans throughout the world. For M. okhotensis from the Okhotsk Sea, most of the females showed left-side insemination (annual average: 95.7%) and most of the males showed left-side asymmetry (99.7%) of the long inner process of the second exopodal segment in the fifth leg throughout the year. However, sympatric M. pacifica showed different ratios of asymmetry for female insemination and male morphotypes with a left : right = 1 : 2 ratio throughout the year. For the seven Metridia species from the global oceans treated in this study, ratios of asymmetry for female insemination and male morphotypes were correlated with each other. One-sided insemination (i.e., only left or only right insemination) was a common pattern for various Metridia species from global oceans, but their ratios varied by species. Previously, low hatching rates (29-68%) of eggs were reported for various Metridia spp. in laboratory experiments, but the reasons for these low rates were unclear. Because each spermatheca of Metridia spp. is connected to the oviduct on the same side, either left or right, this suggests that half of the eggs produced by unilaterally inseminated females remain unfertilized. The morphology of the genital structures and literature data of the egg hatching rates of Metridia spp. indicate that almost half of the eggs produced by females are not viable and are, thus, wasted.
  • K. Matsuno, A. Yamaguchi, S. Nishino, J. Inoue, T. Kikuchi
    BIOGEOSCIENCES 12 13 4005 - 4015 2015年 [査読有り][通常論文]
     
    To evaluate the effect of atmospheric turbulence on a marine ecosystem, high-frequency samplings (two to four times per day) of a mesozooplankton community and the gut pigment of dominant copepods were performed at a fixed station in the Chukchi Sea from 10 to 25 September 2013. During the study period, a strong wind event (SWE) was observed on 18 September. After the SWE, the biomass of chlorophyll a (Chl a) increased, especially for micro-size (> 10 mu m) fractions. The zooplankton abundance ranged from 23 610 to 56 809 ind.m(-2) and exhibited no clear changes as a result of the SWE. In terms of abundance, calanoid copepods constituted the dominant taxa (mean: 57 %), followed by barnacle larvae (31 %). Within the calanoid copepods, small-sized Pseudocalanus spp. (65 %) and large-sized Calanus glacialis (30 %) dominated. In the population structure of C. glacialis, copepodid stage 5 (C5) dominated, and the mean copepodid stage did not vary with the SWE. The dominance of accumulated lipids in C5 and C6 females with immature gonads indicated that they were preparing for seasonal diapause. The gut pigment of C. glacialis C5 was higher at night and was correlated with ambient Chl a, and a significant increase was observed after the SWE (2.6 vs. 4.5 ng pigment ind.(-1)). The grazing impact by C. glacialis C5 was estimated to be 4.14 mgC m(-2) day(-1), which corresponded to 0.5-4.6% of the biomass of the micro-size phytoplankton. Compared with the metabolic food requirement, C. glacialis feeding on phytoplankton accounted for 12.6% of their total food requirement. These facts suggest that C. glacialis could not maintain their population by feeding solely on phytoplankton and that other food sources (i.e., microzooplankton) must be important in autumn. As observed by the increase in gut pigment, the temporal phytoplankton bloom, which is enhanced by the atmospheric turbulence (SWE) in autumn, may have a positive effect on copepod nutrition.
  • Atsushi Yamaguchi, Kohei Matsuno, Tomoe Homma
    ZOOLOGICAL STUDIES 54 13 - 13 2015年01月 [査読有り][通常論文]
     
    Background: Despite its ecological importance, little information is available regarding the spatial and vertical changes in the calanoid copepod community over large geographical regions. This study investigated the spatial and vertical patterns in calanoid copepod abundance and community structure using zooplankton samples collected between depths of 0 and 2,615 m across the North Pacific from 0 degrees to 56 degrees N. Results: A total of 211 calanoid copepod species belonging to 66 genera and 24 families were identified. Calanoid copepod abundance decreased with increasing depth, and few latitudinal differences were detected. Across the entire region, species diversity peaked near 500 to 2,000 m in depth. The calanoid copepod community was separated into seven groups with distinct spatial and vertical distributions. For all groups, the number of species was low (28 to 37 species) in the subarctic region (north of 40 degrees N) and high (116 to 121 species) in the subtropical-tropical region. The deepest group in the subtropical-tropical region was composed of cosmopolitan species, and this group was also observed in deep water in the subarctic region. Conclusions: In deep water, most of the calanoid copepod community consisted of cosmopolitan species, while an endemic community was observed in the subarctic region. Because the food of deep-sea calanoid copepods originates from the surface layer, sufficient and excess flux in the eutrophic subarctic region may be responsible for maintaining the endemic species in the region.
  • Kaede Sato, Kohei Matsuno, Daichi Arima, Yoshiyuki Abe, Atsushi Yamaguchi
    ZOOLOGICAL STUDIES 54 18 - 18 2015年01月 [査読有り][通常論文]
     
    Background: An optical plankton counter (OPC) was used to examine spatial and temporal changes in the zooplankton size spectra in the neighboring waters of Japan from May to August 2011. Results: Based on the zooplankton biovolume of equivalent spherical diameter (ESD) in 45 bins for every 0.1 mm between 0.5 and 5.0 mm, a Bray-Curtis cluster analysis classified the zooplankton communities into six groups. The geographical distribution of each group varied from each of the others. Groups with a dominance of 4 to 5 mm ESD were observed in northern marginal seas (northern Japan Sea and Okhotsk Sea), while the least biovolume with a dominance of a small-size class (0.5 to 1 mm) was observed for the Kuroshio extension. Temporal changes were observed along the 155 degrees E line, i.e., a high biovolume group dominated by 2 to 3 mm ESD during May shifted to other size spectra groups during July to August. These temporal changes were caused by the seasonal vertical descent of dominant large Neocalanus copepods during July to August. As a specific characteristic of the normalized biomass size spectra (NBSS), the slope of NBSS was moderate (-0.90) for the Neocalanus dominant spring group but was at -1.11 to -1.24 for the other groups. Theoretically, the slope of the NBSS of the stable marine ecosystem is known to settle at approximately -1. Conclusions: Based on the analysis by OPC, zooplankton size spectra in the neighboring waters of Japan were separated into six groups. Most groups had -1.11 to -1.24 NBSS slopes, which were slightly higher than the theoretical value (-1). However, one group had a moderate slope of NBSS (-0.90) caused by the dominance of large Neocalanus copepods.
  • Lindsay, D.J, Yamaguchi, A, Grossmann, M.M, Nishikawa, J, Sabates, A, Fuentes, V, Hall, M, Sunahara, K, Yamamoto, H
    Bulletin of the Plankton Society of Japan 61 1 72 - 81 日本プランクトン学会 2014年12月 [査読有り][通常論文]
  • Masafumi Natsuike, Makoto Kanamori, Katsuhisa Baba, Kazuomi Moribe, Atsushi Yamaguchi, Ichiro Imai
    HARMFUL ALGAE 39 271 - 279 2014年10月 [査読有り][通常論文]
     
    The 2011 Great East Japan Earthquake and the subsequent huge tsunami greatly affected both human activity and the coastal marine ecosystem along the Pacific coast of Japan. The tsunami also reached Funka Bay in northern Japan and caused serious damage to the scallop cultures there, and this tsunami was believed to have affected the coastal environments in the bay. Therefore, we investigated the changes in the spatial abundance and distribution of the toxic dinofiagellates Alexandrium tamarense cysts before the tsunami (August 2010) and after the tsunami (May 2011, August 2011, May 2012 and August 2012) in the bay. Further, monthly sampling was conducted after the tsunami to identify seasonal changes of Alexandrium catenella/tamarense cysts and vegetative cells. Significant increases were observed in the populations of A. catenella/tamarense cysts, comparing the abundances before the tsunami (in August 2010; 70 +/- 61 cysts g(-1) wet sediment) to those just after it (in May 2011; 108 +/- 84 cysts g(-1) wet sediment), and both A. tamarense bloom (a maximum density was 1.3 x 10(3) cells L-1) and PSP (Paralytic Shellfish Poisoning) toxin contamination of scallops (9.4 mouse unit g(-1) was recorded) occurred in the bay. Seasonal sampling also revealed that the encystment of A. tamarense and the supply of the cysts to bottom sediments did not occur in the bay from September to April. These results strongly suggested that the mixing of the bottom sediments by the tsunami caused the accumulation of the toxic A. tamarense cysts in the surface of bottom sediment through the process of redeposition in Funka Bay. Moreover, this cyst deposition may have contributed to the toxic bloom formation as a seed population in the spring of 2011. (C) 2014 Elsevier B.V. All rights reserved.
  • Atsushi Yamaguchi, Kohei Matsuno, Yoshiyuki Abe, Daichi Arima, Kohei Ohgi
    DEEP-SEA RESEARCH PART I-OCEANOGRAPHIC RESEARCH PAPERS 91 115 - 124 2014年09月 [査読有り][通常論文]
     
    To identify seasonal patterns of change in zooplankton communities, an optical plankton counter (OPC) and microscopic analysis were utilised to characterise zooplankton samples collected from 0 to 150 m and 0 to 500 m in the Oyashio region every one to three months from 2002 to 2007. Based on the OPC measurements, the abundance and biomass of zooplankton peaked in June (0-150 m) or August (150-500 m), depending on the depth stratum. The peak periods of the copepod species that were dominant in terms of abundance and biomass indicated species-specific patterns. Three Neocalanus species (Neocalanus cristatus, Neocalanus flemingeri and Neocalanus plumchnis) exhibited abundance peaks that occurred before their biomass peaks, whereas Eucalanus bungii and Metridia pacifica experienced biomass peaks before their abundance peaks. The abundance peaks corresponded to the recruitment periods of early copepodid stages, whereas the biomass peaks corresponded to the periods when the dominant populations reached the late copepodid stages (C5 or C6). Because the reproduction of Neocalanus spp. occurred in the deep layer ( > 500 m), their biomass peaks were observed when the major populations reached stage C5 after the abundance peaks of the early copepodid stages. The reproduction of E. bungii and M. paafica occurred near the surface layer. These species first formed biomass peaks of C6 and later developed abundance peaks of newly recruited early copepodid stages. From the comparison between OPC measurements and microscopic analyses, seasonal changes in zooplankton biomass at depths of 0-150 m were governed primarily by E. bungii and M. pacifica, whereas those at depths of 150-500 m were primarily caused by the three Neocalanus species. (C) 2014 Elsevier Ltd. All rights reserved.
  • Kohei Matsuno, Mutsuo Ichinomiya, Atsushi Yamaguchi, Ichiro Imai, Takashi Kikuchi
    POLAR BIOLOGY 37 8 1185 - 1195 2014年08月 [査読有り][通常論文]
     
    The western Arctic Ocean is composed of two regions: the southern shelf and the northern basin, whereas the marine ecosystem structure is expected to vary between the regions, little information is available, particularly for the planktonic protist community. In this study, we surveyed the horizontal distribution of microprotists (diatoms, dinoflagellates and ciliates) at 59 stations in the western Arctic Ocean during September and October of 2010. The abundances of diatoms, dinoflagellates and ciliates were 0-138,640, 0-16,460 and 0-10,933 cells L-1, respectively, and all of the abundances were higher on the Chukchi Sea shelf. Cluster analysis based on abundance separated the microprotist community into five groups, which contain 25, 22, 6, 4 and 2 stations. The largest group was observed on the Chukchi Sea shelf, showing a high abundance predominated by diatoms (78 % of total abundance). The second group was observed from the East Siberian Sea to the Canada Basin, characterised by low abundance and ciliate dominance (36 % of total abundance). Because of the high abundance and predominance of diatoms, the former group is characterised by eutrophic waters, which are enhanced by the continuous inflow of the nutrient-rich Pacific Water through the Bering Strait. Due to the low abundance and the dominance of ciliates, the latter group is dominated by organisms of the microbial food web. The remaining three groups were smaller and located between the two large groups. The distribution of these three groups may be based on complex physical structures, such as the anticyclonic eddy near the shelf break.
  • Eiji Watanabe, Jonaotaro Onodera, Naomi Harada, Makio C. Honda, Katsunori Kimoto, Takashi Kikuchi, Shigeto Nishino, Kohei Matsuno, Atsushi Yamaguchi, Akio Ishida, Michio J. Kishi
    NATURE COMMUNICATIONS 5 3950 - 3950 2014年05月 [査読有り][通常論文]
     
    The future conditions of Arctic sea ice and marine ecosystems are of interest not only to climate scientists, but also to economic and governmental bodies. However, the lack of widespread, year-long biogeochemical observations remains an obstacle to understanding the complicated variability of the Arctic marine biological pump. Here we show an early winter maximum of sinking biogenic flux in the western Arctic Ocean and illustrate the importance of shelf-break eddies to biological pumping from wide shelves to adjacent deep basins using a combination of year-long mooring observations and three-dimensional numerical modelling. The sinking flux trapped in the present study included considerable fresh organic material with soft tissues and was an order of magnitude larger than previous estimates. We predict that further reductions in sea ice will promote the entry of Pacific-origin biological species into the Arctic basin and accelerate biogeochemical cycles connecting the Arctic and subarctic oceans.
  • Daichi Arima, Atsushi Yamaguchi, Yoshiyuki Abe, Kohei Matsuno, Rui Saito, Hiroki Asami, Hiroshi Shimada, Ichiro Imai
    CRUSTACEANA 87 3 364 - 375 2014年03月 [査読有り][通常論文]
     
    Seasonal changes in body size (prosome length: PL) and oil sac volume (OSV) of the three most numerically abundant copepods in Ishikari Bay, northern Sea of Japan, Paracalanus parvus (Claus, 1863), Pseudocalanus newmani Frost, 1989 and Oithona similis Claus, 1866, were studied using monthly samples collected through vertical hauls of a 100-mu m mesh NORPAC net from March, 2001 to May, 2002. Seasonal changes in PL were common for the three species and were more pronounced during a cold spring. PL was negatively correlated with temperature, and this relationship was described well using the Belehradek equation. Seasonal changes in OSV exhibited a species-specific pattern, i.e., OSV was greater during a warm summer for P. parvus and was greater during a cold spring for P. newmani and O. similis. The OSV peak period corresponded with the optimal thermal season of each species. The relative OSV to prosome volume of the small copepods (0.6-0.8%) was substantially lower than that of the large copepods (20-32%). These facts suggest that the oil sac of small copepods is not used for overwintering or diapauses or during periods of food scarcity, but is instead used as the primary energy source for reproduction, which occurs during the optimum thermal season of each species.
  • Yuka Onishi, Yuka Mohri, Akihiro Tuji, Kohei Ohgi, Atsushi Yamaguchi, Ichiro Imai
    FISHERIES SCIENCE 80 2 353 - 362 2014年03月 [査読有り][通常論文]
     
    Seagrasses are known to have allelopathic activity to reduce growth of phytoplankton. We found growth-inhibiting bacteria (strains E8 and E9) from Zostera marina possessing strong activity against the toxic dinoflagellate Alexandrium tamarense. Strain E9 markedly inhibited growth of A. tamarense even with initial inoculum size as small as 2.9 cells ml(-1). This bacterium also had growth-inhibiting effects on the red-tide raphidophytes Chattonella antiqua and Heterosigma akashiwo, the dinoflagellate Heterocapsa circularisquama, and the diatom Chaetoceros mitra. Small subunit (SSU) ribosomal DNA (rDNA) sequencing analysis demonstrated that the most probable affiliation of these strains was Flavobacteriaceae, and proved that another inhibitory bacterial strain (E8) was the same species as strain E9. Two other bacterial strains (E4-2 and E10), showing different colony color and isolated from the same seagrass sample, revealed no growth-inhibiting activity. Interestingly, strain E4-2 showed the same sequences as E8 and E9 (100 %), and strain E10 matched E8 and E9 with 99.80 % similarity. Growth-inhibiting bacteria against the toxic dinoflagellate Alexandrium tamarense associated with seagrass, such as Flavobacterium spp. E8 and E9, are able to repress shellfish poisoning besides the allelopathic activity of seagrass itself.
  • Kohei Matsuno, Atsushi Yamaguchi, Amane Fujiwara, Jonaotaro Onodera, Eiji Watanabe, Ichiro Imai, Sanae Chiba, Naomi Harada, Takashi Kikuchi
    JOURNAL OF PLANKTON RESEARCH 36 2 490 - 502 2014年03月 [査読有り][通常論文]
     
    To examine seasonal changes in the mesozooplankton community, analyses were made on the swimmer samples (>1 mm) collected by a sediment trap mooring at 184 m depth on the Northwind Abyssal Plain in the western Arctic Ocean during October 2010-September 2011. The zooplankton swimmer flux ranged from 5 to 44 ind. m(-2) day(-1) and was greater during July to October; copepods were the dominant taxon. Based on the zooplankton swimmer flux, cluster analysis classified samples into three groups (A, B-1 and B-2). The occurrence of each group showed clear seasonality; group A was observed during July to October, group B-1 was seen in November to January and group B-2 during March to June. The seasonal variability in population structures of four dominant copepod swimmers was clearly different between the species. Most Calanus hyperboreus were copepodid stage 6 female (C6F) throughout the year. For Metridia longa and Paraeuchaeta glacialis, C6Fs dominated during January to May, and early copepodid stages increased during June to October. Heterorhabdus norvegicus was dominated by stage C5 during November to February, and C6F/M during March to May. Since Pacific copepods (Neocalanus cristatus) occurred in significant number during August-September, possible causes are discussed.
  • Atsushi Yamaguchi, Dhugal Lindsay, Kazuhiko Koike
    Bulletin of the Plankton Society of Japan 61 1 32 - 33 2014年02月 [査読有り][通常論文]
  • Arima, D, Yamaguchi, A, Abe, Y, Matsuno, K, Saito, R, Asami, H, Shimada, H, Imai, I
    Bulletin of the Fisheries Sciences, Hokkaido University 64 1 17 - 23 北海道大学大学院水産科学研究院 2014年 [査読無し][通常論文]
     
    Seasonal changes in the zooplankton community in Ishikari Bay, northern Japan Sea were studied based on monthly samplescollected by vertical hauls of a 100 μm mesh NORPAC net from March 2001 to May 2002. Zooplankton abundancepeaked in May and was mainly composed of copepodid stages of copepods. Cluster analysis of copepod abundance separatedthe community into two main groups : group A was observed from January to June (winter and spring) and group B from July toDecember (summer and autumn). Groups A and B were composed of cold and warm water species, respectively. Speciesdiversity was high for group B. As the second dominant taxa, copepod nauplii dominated during winter and spring, whereasmolluscs and appendicularians were abundant during summer and autumn. Copepod nauplii in winter and spring likely reflectthe copepod reproduction initiated by spring the phytoplankton bloom. Molluscs in summer and autumn were composed ofplanktonic larvae of benthos (=meroplankton). Appendicularians during summer and autumn are oceanic and considered tohave been transported by the Tsushima warm current. High copepod species diversity during summer and autumn might alsobe related to the Tsushima warm current.
  • Rui Saito, Atsushi Yamaguchi, Ichiro Yasuda, Hiromichi Ueno, Hiromu Ishiyama, Hiroji Onishi, Ichiro Imai
    JOURNAL OF PLANKTON RESEARCH 36 1 117 - 128 2014年01月 [査読有り][通常論文]
     
    Mesoscale anticyclonic eddies have been observed south of the Aleutian Islands. Eddies farther east, in the Gulf of Alaska, are known to transport coastal water and coastal zooplankton to the offshore open ocean. The impacts of mesoscale anticyclonic eddies formed south of the western Aleutian Islands (Aleutian eddies) on the zooplankton community are not fully understood. In the present study, we describe zooplankton population structures within an Aleutian eddy and outside the eddy during July 2010. Based on the sea-level anomaly, the Aleutian eddy was formed south of Attu Island (172 degrees 54'E) in February 2010, and it moved southeastward in the next 5 months. Large oceanic copepods, Neocalanus cristatus, Eucalanus bungii and Metridia pacifica were more abundant inside the eddy than the outside. Inside the eddy, the life stage distribution of N. cristatus was more advanced than that outside, and Neocalanus spp. had accumulated more lipids. These conditions probably reflect the greater primary production in the eddy, production enhanced by nutrients advected into the eddy. The Aleutian eddy contained mostly oceanic copepods because it was formed in the offshore water and/or eddy-eddy interaction occurred after its formation. The sufficient food condition in the eddy presumably resulted in higher growth and survival rates of these oceanic copepods, resulting in the greater abundance, advanced development stages and greater lipid accumulation.
  • Yamaguchi A, Homma T, Saito R, Matsuno K, Ueno H, Hirawake T, Imai I
    Plankton and Benthos Research 8 3 116 - 123 2014年 [査読有り][通常論文]
     
    Stratified zooplankton sampling was conducted in the subarctic Pacific in June 2009 at four stations along 47°N from 0 to 3,000 m depth to evaluate longitudinal changes in population structure and vertical distribution of the dominant copepod species. At the westernmost station (160°E), the population structure of Eucalanus bungii and Metridia pacifica was dominated by early copepodid stages. In E. bungii, nauplii were abundant and adult females had developed ovaries at 160°E, while at the three stations to the east (167°E, 174°E and 179°W), no E. bungii nauplii were collected, and the resting stages were dominant. This suggests the species was reproducing near 160°E and in diapause in the east. In all three Neocalanus species analyzed (N. cristatus, N. flemingeri and N. plumchrus), late copepodid stages were dominant at the eastern three stations. Lipid accumulation in the fifth copepodid stage of Neocalanus spp. was greater in the west than in the east. This probably resulted from better food conditions and lower temperatures in the west, where copepods could consume more food during development than in the east.
  • Yasuhide Nakamura, Ichiro Imai, Atsushi Yamaguchi, Akihiro Tuji, Noritoshi Suzuki
    Plankton and Benthos Research 8 3 107 - 115 2014年 [査読有り][通常論文]
     
    Zooplankton samples from the deep water of the Sea of Japan often contain yellowish semitransparent spheres (1.0-1.5 mm in diameter). We recognized these spheres as a single phaeodarian species (Cercozoa, Rhizaria) and described them as Aulographis japonica sp. nov. (family Aulacanthidae) in this paper. This species has a high abundance in the Japan Sea Proper Water (JSPW) and occasionally higher biomass than that of copepods. Molecular analysis based on 18S SSU rDNA revealed that Aulacantha scolymantha, which belongs to the same family as A. japonica, is closer to Aulosphaera trigonopa and Protocystis spp., which belong to different orders, than to the present species. The distribution of A. japonica is apparently restricted to low temperature water. Its biomass was the highest in the uppermost layer of JSPW, and this phaeodarian species was the second most important zooplankton below 250 m depth in terms of biomass among the total zooplankton groups. This is probably due to its generalist type of feeding. Considering its large biomass, A. japonica possibly plays an important role in matter cycles within the Sea of Japan.
  • Abe, Y, Yamaguchi, A, Matsuno, K, Kono, T, Imai, I
    Bulletin of the Fisheries Sciences, Hokkaido University 64 3 71 - 81 北海道大学大学院水産科学研究院 2014年 [査読無し][通常論文]
     
    To evaluate the effects of water mass changes and the spring phytoplankton bloom, we analysed short-term changes in thepopulation structure of the dominant hydromedusa Aglantha digitale in the Oyashio region during March-April 2007. Sampleswere collected with Bongo nets at night via oblique towing from a depth of 200 m to the surface on eight occasions in March andApril of 2007. The abundance, biomass and mature individual compositions of A. digitale rapidly increased from Aprilonward. During April, the reproduction and growth of A. digitale is achieved due to the initiation of the spring phytoplanktonbloom and the increase in small copepods. Based on dry mass, the growth rate of A. digitale (1.3% day-1) was lower than thereported maximum value (4.9% day-1) for this species. The rapid exchange of the dominant water masses was also observedduring spring in the Oyashio region. Significant effects of water mass exchange were detected in the abundance, biomass andbody sizes of A. digitale. Thus, the abundance, biomass and population structure of A. digitale in the Oyashio region may bealtered during spring by two factors : internal growth and external water mass exchange.
  • 大西由花, 山口 篤, 今井一郎
    北海道大学水産科学研究彙報 64 2 45 - 54 北海道大学大学院水産科学研究科編集出版委員会 2014年 [査読無し][通常論文]
     
    Temporal fluctuations of bacteria, heterotrophic nanoflagellates (HNF), autotrophic nanoflagellates (ANF) and ciliates wereinvestigated from spring to early summer at the stations in Akkeshi-ko Estuary with large scale seagrass bed of Zostera marinaand Akkeshi Bay, Eastern Hokkaodo, Japan. The ranges of bacterial density were 5.4×105-3.0×106 cells mL-1 in Akkeshi-koEstuary (Stn. 1) and 2.3×105-1.9×106 cells mL-1 in Akkeshi Bay (Stns. 2, 3). The ranges of HNF were 3.1×102-3.3×103cells mL-1 in the estuary and 2.2×101-1.1×103 cells mL-1 in the bay. The densities of ANF were 1.8×102-5.0×104 cells mL-1(Stn. 1) and 2.2×101-3.6×104 cells mL-1 (Stns. 2, 3). The densities of microorganisms were higher in the coastal area than offshore. In contrast, ciliate densities were <80-9.8×103 inds. L-1 in the estuary and <80-1.1×104 inds. L-1 in the bay. Significantcorrelations were found between HNF and ANF, temperature and them, suggesting that major parts of ANF were mixotrophsof bacterial grazers like HNF.
  • Yoshiyuki Abe, Masafumi Natsuike, Kohei Matsuno, Takeshi Terui, Atsushi Yamaguchi, Ichiro Imai
    JOURNAL OF EXPERIMENTAL MARINE BIOLOGY AND ECOLOGY 449 321 - 329 2013年11月 [査読有り][通常論文]
     
    The assimilation efficiency of zooplankton is an essential parameter required to estimate energy transfer to higher trophic levels in marine ecosystems. However, little information is available for large oceanic copepods, especially the Neocalanus and Eucalanus species dominant in the subarctic Pacific. In this study, the assimilation efficiencies of the C5 stages of Neocalanus cristatus, Neocalanus flemingeri and Eucalanus bungii were evaluated using eight phytoplankton species as food. The average assimilation efficiencies of N. cristatus, N. flemingeri and E. bungii ranged between 45 and 66%, 44 and 66% and 34 and 65%, respectively. The assimilation efficiency was highly variable depending on the food phytoplankton species. In all species, the assimilation efficiency showed a significant negative relationship with the ash content of the phytoplankton (r(2) = 0.79-0.87, p<0.001). The assimilation efficiency of large-body sized N. cristatus for large-sized diatoms was higher than for the other copepod species. In population models of N. cristatus, changes in assimilation efficiency affect the growth and survival rates of the population. The Lagrangian ensemble model (LEM) for N. cristatus showed that, for assimilation efficiencies less than 57%, the population could not be maintained. Because variations in assimilation efficiency may have significant effects on the copepod population, their variability should be incorporated into marine ecosystem models in the future. (C) 2013 Elsevier B.V. All rights reserved.
  • Yasuhiro Takenaka, Akiko Noda-Ogura, Tadashi Imanishi, Atsushi Yamaguchi, Takashi Gojobori, Yasushi Shigeri
    Gene 528 2 201 - 205 2013年10月10日 [査読有り][通常論文]
     
    We recently reported the cDNA sequences of 11 copepod luciferases from the superfamily Augaptiloidea in the order Calanoida. They were classified into two groups, Metridinidae and Heterorhabdidae/Lucicutiidae families, by phylogenetic analyses. To elucidate the evolutionary processes, we have now further isolated 12 copepod luciferases from Augaptiloidea species ( Metridia asymmetrica, Metridia curticauda, Pleuromamma scutullata, Pleuromamma xiphias, Lucicutia ovaliformis and Heterorhabdus tanneri). Codon-based synonymous/nonsynonymous tests of positive selection for 25 identified copepod luciferases suggested that positive Darwinian selection operated in the evolution of Heterorhabdidae luciferases, whereas two types of Metridinidae luciferases had diversified via neutral mechanism. By in silico analysis of the decoded amino acid sequences of 25 copepod luciferases, we inferred two protein sequences as ancestral copepod luciferases. They were expressed in HEK293 cells where they exhibited notable luciferase activity both in intracellular lysates and cultured media, indicating that the luciferase activity was established before evolutionary diversification of these copepod species. © 2013 Elsevier B.V.
  • Rie Ohashi, Atsushi Yamaguchi, Kohei Matsuno, Rui Saito, Nao Yamada, Anai Iijima, Naonobu Shiga, Ichiro Imai
    DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY 94 44 - 56 2013年10月 [査読有り][通常論文]
     
    On the southeastern Bering Sea shelf, mesozooplankton plays an important role in material transfer between primary producers and fisheries resources. The biomass of mesozooplankton in this region is known to vary annually, but little is known about annual changes in community structure and species composition. In the present study, regional and long-term changes in abundance, biomass and community structure of copepods and chaetognaths on the shelf were evaluated based on NORPAC net samples collected during summers of 1994-2009. During the study period, regime shifts occurred from high interannual variability regime (1994-1999) to low interannual variability regime with high temperature (2000-2005), then to a low interannual variability regime with low temperature (2007-2009). A total of 24 calanoid copepod species belonging to 21 genera were identified from samples. Copepod abundance ranged from 150 to 834,486 inds. m(-2), was greatest on the Middle shelf, and was higher in cold years, than in warm years. Copepod biomass ranged from 0.013 to 150 g DM m(-2), and was also higher in cold years than in warm years. Based on the results of cluster analysis, the copepod community was divided into six groups (A-F). The regional and interannual distributions of each group were distinct. Interannual changes in abundance of the dominant copepod on the Outer shelf and Middle shelf were highly significant (p < 0.0001), and their abundances were negatively correlated with temperature and salinity. Interannual changes in copepod community that occurred between cold and warm years are thought to have been caused by differences in the magnitude and timing of the spring phytoplankton bloom between the two regimes. Abundance and biomass of the chaetognath Parasagitta elegans ranged from 30 to 15,180 inds. m(-2) and from 11 to 1559 mg DM m(-2), respectively. Chaetognath abundance was significantly correlated with the abundance of the dominant copepods (p < 0.0001). Differences in cold and warm years may also affect recruitment of walleye pollock. We conclude that on the southeastern Bering Sea shelf, the magnitude and timing of primary production, which is related to climate change, may significantly affect how it is transferred through the food web. (C) 2013 Elsevier Ltd. All rights reserved.
  • Chiko Tsukazaki, Ken-Ichiro Ishii, Rui Saito, Kohei Matsuno, Atsushi Yamaguchi, Ichiro Imai
    DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY 94 22 - 30 2013年10月 [査読有り][通常論文]
     
    Information on diatom resting stages is fundamentally important to understanding the population dynamics of diatoms including bloom formation. The distribution of viable diatom resting stage cells in bottom sediments of the eastern Bering Sea in July 2009 was investigated by the most probable number (MPN) method. The abundances of diatom resting stage cells ranged from 1.7 x 10(3) to 1.2 x 10(6) MPN cells cm(-3) wet sediment, comparable to those in shallow eutrophic areas where diatom blooms frequently occur. Common species during the spring phytoplankton bloom in the eastern Bering Sea were also dominant in sediments as resting stage cells. It should be noted that relatively high numbers of ice algae species, especially ribbon-shaped chain forming pennate diatoms, were found in the sediments. The life cycle strategy using resting stage cells allows planktonic and ice algal species to survive unfavorable environmental conditions such as the dark winter season, and potentially contribute to form blooms of several types (subsurface of ice, ice edge, plankton) through vertical mixing. (C) 2013 Elsevier Ltd. All rights reserved.
  • Masafumi Natsuike, Satoshi Nagai, Kohei Matsuno, Rui Saito, Chiko Tsukazaki, Atsushi Yamaguchi, Ichiro Imai
    HARMFUL ALGAE 27 52 - 59 2013年07月 [査読有り][通常論文]
     
    Abundance and distribution of the toxic dinoflagellate Alexandrium tamarense species complex resting cyst were investigated in the eastern Bering Sea and the Chukchi Sea for the first time. Sediment samples (top 0-3 cm depth) were collected from the continental shelf of the eastern Bering Sea (17 stations) and the Chukchi Sea (13 stations) together with a long core sample (top 0-21 cm depth) from one station in the Chukchi Sea during 2009-2012. The cysts were enumerated using the primuline staining method. Species identification of the cysts was carried out with multiplex PCR assay and the plate morphology of vegetative cells germinated from cysts in the both areas. Alexandrium cysts were widely detected in the both areas, ranging from not detected (<1 cysts cm(-3)) to 835 cysts cm(-3) wet sediment in the eastern Bering Sea and from not detected (<1 cysts cm(-3)) to 10,600 cysts cm(-3) in the Chukchi Sea, and all isolated cysts were genetically and morphologically identified as the North American clade A. tamarense. Their cysts were mainly distributed in the shallow continental shelf where the water depth was less than 100 m in both areas. The cysts were detected from the deep layer (18-21 cm depth of sediment core) of the long core sample. The present study confirmed the abundant existence of A. tamarense with wide range of distribution in these areas. This fact suggests that A. tamarense vegetative cells have appeared in the water column in the both areas. Furthermore, these abundant cyst depositions indicate that this species originally distributed in the Arctic and subarctic regions and well adapted to the environments in the marginal ice zone. (C) 2013 The Authors. Published by Elsevier B.V. All rights reserved.
  • Kana Chikugo, Atsushi Yamaguchi, Kohei Matsuno, Rui Saito, Ichiro Imai
    CRUSTACEANA 86 4 449 - 474 2013年04月 [査読有り][通常論文]
     
    Pelagic Mysidacea and Decapoda have important roles in marine ecosystems. However, information on their life histories is extremely limited. This study aimed to evaluate the life cycles of pelagic Mysidacea and Decapoda in the Oyashio region, Japan. Production of the four dominant species was estimated by combining body mass (DM) data and abundance data Mysidacea belonging to 5 species from 5 genera occurred in the study area. Their abundance and biomass ranged between 11.7-50.1 ind. m(-2) and 1.2-7.9 g wet mass (VIM) m(-2), respectively. Six species from 6 genera belonged to Decapoda, and their abundance and biomass ranged between 9.0-17.3 ind. M-2 and 3.0-17.3 g WM M-2, respectively. Based on body length histograms, there were two to four cohorts for the three dominant mysids and one dominant decapod on each sampling date. Life histories of the two numerically dominant mysids (Eucopia australis and Boreomysis californica) followed similar patterns: recruitment of young in May, strong growth from April to June, and a longevity of three years. Life cycles of the two minor species (the mysid Meterythrops microphthalma and the decapod Hymenodora frontalis) were not clear because of their low abundance. The timing of recruitment of the young and the strong juvenile growth for the two dominant mysids corresponds with the season when their prey is abundant. The annual production of the dominant mysid species was 14.0 mg DM M-2 (B. californica) and 191.8 mg DM m(-2) (E. australis). Annual production/biomass (P / B) ratios ranged between 0.242 (H. frontalis) and 0.643 (M. microphthalma). Compared with other regions, the Oyashio region showed high production and low P / B ratios. The high production in the Oyashio region may be related to the high biomass of these species. Because of the low temperature conditions (3 degrees C), pelagic mysids and decapods in the Oyashio region may have slower growth, longer generation times and lower P / B ratios than in other oceans.
  • 塩田知也, 阿部義之, 齋藤 類, 松野孝平, 山口 篤, 今井一郎
    北海道大学水産科学研究彙報 63 1 13 - 22 北海道大学大学院水産科学研究科 2013年 [査読無し][通常論文]
     
    海洋生態系において，動物プランクトンのサイズ毎の現存量を把握することは，動物プランクトンのサイズ組成が，魚類仔稚魚の餌選択性，成長および生残に影響を与えること，また鉛直的な有機物輸送量を決定することから，水産学および海洋学いずれの視点においても重要である。動物プランクトンサイズ組成に関する情報はその重要性にも関わらず，特にその時空間変動に関する知見は乏しいのが現状である。その理由として，従来の顕微鏡による解析には多大な労力，膨大な時間および動物プランクトンの形態分類についての専門的な知識が必要となることが挙げられる。こうした問題の解決策として，従来の顕微鏡解析に比べて正確，簡便かつ短時間にサイズ分布の解析が可能な光学式プランクトンカウンター(OPC: Optical Plankton Counter; Herman，1988)が導入されている。
  • Dhugal Lindsay, Hiroshi Yoshida, Shojiro Ishibashi, Mitsuko Umetsu, Atsushi Yamaguchi, Hiroyuki Yamamoto, Jun Nishikawa, James Davis Reimer, Hiromi Watanabe, Katsunori Fujikura, Tadashi Maruyama
    2013 IEEE INTERNATIONAL UNDERWATER TECHNOLOGY SYMPOSIUM (UT) 2013年 [査読無し][通常論文]
     
    A recently developed untethered but remotely operated survey platform, the PICASSO system, is described. This vehicle was designed specifically for surveys of macro- and megazooplankton and marine particulates (maximum depth 1000 m), to link information on gelatinous zooplankton diversity, behaviour and community structure with their function as packagers and producers of marine snow. In addition, an autonomous Visual Plankton Recorder, which is also deployable on the PICASSO vehicle, has been used to investigate particle profiles and plankton distribution vs. depth. Some results from these two systems from eastern Antarctica, the Coral Sea in Australia, and off Japan are introduced. Other techniques for imaging plankton in three dimensions are also introduced.
  • Kohei Matsuno, Atsushi Yamaguchi, Ichiro Imai
    ICES JOURNAL OF MARINE SCIENCE 69 7 1205 - 1217 2012年09月 [査読有り][通常論文]
     
    An optical plankton counter was used to examine the regional characteristics of the zooplankton communities in the Chukchi Sea during the summers of 1991, 1992, 2007, and 2008. Zooplankton abundance and biomass ranged from 5000 to 1 170 000 ind. m(-2) and 0.2 to 10.9 g dry mass m(-2), respectively. Based on zooplankton biovolume in equivalent spherical diameter (ESD) in 48 bins, one every 0.1 mm between 0.25 and 5.0 mm, a Bray-Curtis cluster analysis classified zooplankton communities into four groups (A-D). No changes were observed in zooplankton communities south of the Lisburne Peninsula (group A) throughout the 4 years, but there were differences north of the Peninsula, with group B (normal, intermediate biomass) observed in 1991/1992, group D (low biomass) in 2007, and group C (predominance of barnacle larvae) in 2008. Analysis of the normalized biomass size spectra for the groups indicated that groups A and C were very productive, so the zooplankton community south of the Lisburne Peninsula was consistently highly productive, which may be because of the continuous inflow of Pacific Water rich in nutrients. Zooplankton communities north of the Lisburne Peninsula varied greatly from year to year, which may be related to interannual changes in sea-ice extent.
  • 山口 篤, 小鳥 守之
    日本プランクトン学会報 59 2 98 - 101 日本プランクトン学会 2012年08月 [査読有り][通常論文]
  • Yoshiyuki Abe, Ken-ichiro Ishii, Atsushi Yamaguchi, Ichiro Imai
    DEEP-SEA RESEARCH PART I-OCEANOGRAPHIC RESEARCH PAPERS 65 100 - 112 2012年07月 [査読有り][通常論文]
     
    To evaluate the responses to the spring phytoplankton bloom, short-term changes in population structure and vertical distribution of mesopelagic copepods (Gaetanus simplex, Gaidius variabilis, Pleuromamma scutullata, Paraeuchaeta elongata, P. birostrata, Heterorhabdus tanneri and Heterostylites major) were studied in the Oyashio region. Samples were collected with a 60 mu m mesh VMPS from 9 strata between 0 and 1000 m both day and night on five occasions during March-April 2007. All the species except Heterorhabdidae species performed reproduction during the spring phytoplankton bloom, while no recruitment to copepodid stages was detected because the newly born individuals were eggs or nauplii. The shallower-living species, G. simplex, P. scutullata and P. elongata had nocturnal ascent did l vertical migration (DVM). While suspension feeding copepods cease DVM after 11 April (P. scutullata) or 23 April (G. simplex), carnivorous P. elongata continued DVM over the study period. Since the gut contents of G. simplex showed a nocturnal increment even in the period of no DVM (23 and 29 April), they might be feeding at depth without DVM. Thus, the cessation of DVM in mesopelagic suspension feeding copepods would be induced by the increase of sinking particles (e.g. food for suspension feeders) during the spring phytoplankton bloom. (C) 2012 Elsevier Ltd. All rights reserved.
  • Yasuhiro Takenaka, Atsushi Yamaguchi, Naoki Tsuruoka, Masaki Torimura, Takashi Gojobori, Yasushi Shigeri
    MOLECULAR BIOLOGY AND EVOLUTION 29 6 1669 - 1681 2012年06月 [査読有り][通常論文]
     
    Copepods are the dominant taxa in zooplankton communities of the ocean worldwide. Although bioluminescence of certain copepods has been known for more than a 100 years, there is very limited information about the structure and evolutionary history of copepod luciferase genes. Here, we report the cDNA sequences of 11 copepod luciferases isolated from the superfamily Augaptiloidea in the order Calanoida. Highly conserved amino acid residues in two similar repeat sequences were confirmed by the multiple alignment of all known copepod luciferases. Copepod luciferases were classified into two groups of Metridinidae and Heterorhabdidae/Lucicutiidae families based on phylogenetic analyses, with confirmation of the interrelationships within the Calanoida using 18S ribosomal DNA sequences. The large diversity in the specific activity of planktonic homogenates and copepod luciferases that we were able to express in mammalian cultured cells illustrates the importance of bioluminescence as a protective function against predators. We also discuss the relationship between the evolution of copepod bioluminescence and the aspects of their ecological characteristics, such as swimming activity and vertical habitat.
  • Phyllis J. Stabeno, Nancy B. Kachel, Sue E. Moore, Jeffrey M. Napp, Michael Sigler, Atsushi Yamaguchi, Alexandre N. Zerbini
    DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY 65-70 31 - 45 2012年06月 [査読有り][通常論文]
     
    The southeastern, middle shelf of the Bering Sea has exhibited extreme variability in sea ice extent, temperature, and the distribution and abundance of species at multiple trophic levels over the past four decades. From 1972-2000, there was high interannual variability of areal extent of sea ice during spring (March-April). In 2000, this shifted to a 5-year (2001-2005) period of low ice extent during spring, which transitioned to a 4-year (2007-2010) period of extensive sea ice. High (low) areal extent of sea ice in spring was associated with cold (warm) water column temperatures for the following 6-7 months. The ocean currents also differed between warm and cold years. During cold years, the monthly-mean currents over the shelf were largely westward, while in warm years the direction of currents was more variable, with northward flow during December-February and relatively weak flow during the remainder of the year. The types and abundance of zooplankton differed sharply between warm and cold years. This was especially true during the prolonged warm period (2001-2005) and cold period (2007-2010), and was less evident during the years of high interannual variability. During the warm period, there was a lack of large copepods and euphausiids over the shelf; however, their populations rebounded during cold period. Small crustacean zooplankton taxa did not appear to vary between and warm and cold years. For both walleye pollock and Pacific cod, year-class strength (recruitment) was low during the prolonged warm period, but improved during the following cold period. Year-class strength did not appear to vary as a function of warm and cold years during the period of high year-to-year variability. Also, recruitment of arrowtooth flounder (a predator of pollock and cod) did not appear influenced by the warm or cold years. Finally, the distribution and relative abundance of fin whales appeared to differ in warm and cold years, with fewer whales on the southeastern, middle shelf during warm years. (C) 2012 Elsevier Ltd. All rights reserved.
  • Sanae Chiba, Hiroya Sugisaki, Akira Kuwata, Kazuaki Tadokoro, Toru Kobari, Atsushi Yamaguchi, David L. Mackas
    PROGRESS IN OCEANOGRAPHY 97 63 - 75 2012年05月 [査読有り][通常論文]
     
    Regional differences in the mechanisms of temporal variation in the lower trophic levels in the western, central, and eastern subarctic North Pacific were studied using the nitrogen stable isotope ratio (delta N-15) of the major copepod species, Neocalanus cristatus, Neocalanus flemingeri, and Neocalanus plumchrus. We used formalin-preserved specimens collected in the Oyashio region (OY), three sections from north to south along the 180 degrees longitudinal line (180LineSA, TN, and TS), off Vancouver Island (Off-Van), and at Sta. P. during the periods of 1960-2000, 1979-1997, 1981-2007, and 1996-2007, respectively. The regional mean delta N-15 of the three species roughly corresponded to the surface nitrate distribution and the extent of its drawdown from winter to spring; it was higher in regions of larger seasonal drawdown as observed in the coastal regions OY and Off-Van (7-10 parts per thousand) but lower in regions with less seasonal drawdown, such as in the offshore regions at St. P and stations along the 180Line (3-6 parts per thousand). Time series analysis revealed possible region-specific mechanisms for temporal variation in Neocalanus delta N-15. First, delta N-15 indicated shifts in feeding strategies between herbivorous to omnivorous/carnivorous at OY and 180LineSA, where delta N-15 tended to be lower in the years with warmer winters, suggesting that Neocalanus took advantage of enhanced phytoplankton production under favorable light availability due to increased stratification. Conversely, wind-induced latitudinal advection of surface water was considered to be the initial cause of interannual variation in Neocalanus delta N-15 at 180LineTN, 180LineTS, and Off-Van, where delta N-15 was higher in the years with strong southerly or westerly winds at 180LineTN and TS, and the Off-Van site. This suggests that pole-ward transport of relatively oligotrophic, southern water might enhance the uptake of the heavier isotope by phytoplankton, which Neocalanus feed upon. Another possibility at the Off-Van site, where high delta N-15 was observed (ca., 8-10 parts per thousand), is a switch in the Neocalanus feeding strategy induced by decreased phytoplankton availability. This study demonstrated the usefulness of zooplankton delta N-15 as an indicator of interannual variation in lower trophic level environments and food web structures, which are caused by region-specific mechanisms. (C) 2011 Elsevier Ltd. All rights reserved.
  • Kohei Matsuno, Atsushi Yamaguchi, Koji Shimada, Ichiro Imai
    POLAR SCIENCE 6 1 105 - 119 2012年04月 [査読有り][通常論文]
     
    The horizontal distribution of the epipelagic zooplankton communities in the western Arctic Ocean was studied during August October 2008. Zooplankton abundance and biomass were higher in the Chukchi Sea, and ranged from 3,000 to 274,000 ind. m(-2) and 5-678 g WM m(-2), respectively. Copepods were the most dominant taxa and comprised 37-94% of zooplankton abundance. For calanoid copepods, 30 species belonging to 20 genera were identified. Based on the copepod abundance, their communities were classified into three groups using a cluster analysis. The horizontal distribution of each group was well synchronized with depth zones, defined here as Shelf, Slope and Basin. Neritic Pacific copepods were the dominant species in the Shelf zone. Arctic copepods were substantially greater in the Slope zone than the other regions. Mesopelagic copepods were greater in the Basin zone than the other regions. Stage compositions of large-sized Arctic copepods (Calanus glacialis and Metridia longa) were characterized by the dominance of late copepodid stages in the Basin. Both the abundance and stage compositions of large copepods corresponded well with Chl. a concentrations in each region, with high Chl. a in the Shelf and Slope supporting reproduction of copepods resulting in high abundance dominated by early copepodid stages. (C) 2012 Elsevier B.V. and NIPR. All rights reserved.
  • Shiota T, Yamaguchi A, Saito R, Imai I
    Bulletin of the Fisheries Sciences, Hokkaido University 62 3 63 - 69 北海道大学大学院水産科学研究院 2012年 [査読無し][通常論文]
     
    Geographical variations in abundance and body size of the hydromedusa Aglantha digitale (O.F. Müller, 1766) were evaluated in the northern North Pacific (NP), the water around Aleutian Islands (AL), eastern Bering Sea shelf (BS) and Chukchi Sea (CH) during the summers of 2007 and 2008. Abundances of A. digitale ranged between 38 and 221 ind. m-2, and had significant inverse relationships with the proportion of mature individuals. While abundances showed large annual variability, body sizes had a common regional pattern both 2007 and 2008. Body size and minimum size of maturity A. digitale were smaller in the BS and CH than those in the NP and AL. The smaller size at maturity in the BS and CH suggests regional variations in the acquired energy budget. The rapid maturity and reproduction in the BS and CH may indicate that they utilize acquired energy to mature and reproduce from smaller body sizes, while slow maturity in the NP and AL may imply that they convert acquired energy to somatic growth first.
  • Rui Saito, Atsushi Yamaguchi, Sei-Ichi Saitoh, Kenshi Kuma, Ichiro Imai
    Plankton and Benthos Research 7 2 96 - 99 2012年 [査読有り][通常論文]
     
    The aim of this study is to evaluate regional and interannual changes in abundance, biomass and body size of the hydromedusa Aglantha digitale in the subarctic Pacific. A. digitale was sampled by 0-150 m vertical tows using a 100 µm mesh-size NORPAC net at stations from 41°30'N to 49°30'N along the 165°E line (western subarctic Pacific) and from 39°00'N to 53°30'N along the 165°W line (eastern subarctic Pacific) during the summers of 2003-2006. The mean numerical abundances during the course of the study in the west and east were 32.9 (range, 0-368) and 169.2 (0-768) ind. m-2, respectively, and those of biomass were 26.3 (0-264) and 69.1 (0-418) mg DM m-2, respectively. The abundance and biomass showed no significant north-south or year-to-year differences within each transect but they were significantly greater in the east in some years. The body size was characterized with the dominance of small-sized individuals in the east. The higher abundance and biomass, and smaller body size in the east were probably due to sampling during or just after their reproduction in the east. © 2012, The Plankton Society of Japan, The Japanese Association of Benthology. All rights reserved.
  • Jumpei Fukuda, Atsushi Yamaguchi, Kohei Matsuno, Ichiro Imai
    Plankton and Benthos Research 7 2 64 - 74 2012年 [査読有り][通常論文]
     
    To evaluate zooplankton interannual and latitudinal changes, Optical Plankton Counter analyses were made on preserved net zooplankton samples collected by NORPAC net from 0-150 m at 35°N-51°N stations along 180° in the central North Pacific during early-mid June 1981-2000. The mean numerical abundance of total zooplankton for the 20 years varied latitudinally from 19,200 to 84,300 ind. m-2but the differences between the three oceanic domains were not significant. However, highly significant latitudinal changes were observed in the mean zooplankton biomass, which ranged from 1.44 to 13.2 mg dry mass m-2with higher values in the Transitional Domain (TR) than in the Subarctic and Subtropical Domains. The high biomass in the TR was caused by the dominance of large-sized zooplankton with equivalent spherical diameters (ESD) of 2-4 mm, regarded to consist mainly of Neocalanus spp. C5. Both the slope and intercept of the Normalized Biomass Size Spectrum also showed significant latitudinal changes with a moderate slope and low intercept in the TR due to the dominance of large zooplankton with 2-4 mm ESD in biomass. In contrast to these large latitudinal changes, only limited interannual variations were observed for zooplankton abundance and biomass in the central North Pacific during the study period. © 2012, The Plankton Society of Japan, The Japanese Association of Benthology. All rights reserved.
  • Kohei Matsuno, Atsushi Yamaguchi, Toru Hirawake, Ichiro Imai
    POLAR BIOLOGY 34 9 1349 - 1360 2011年09月 [査読有り][通常論文]
     
    A recent drastic decrease in sea ice cover area was observed in the western Arctic Ocean during summer, yet little information is available for its effect on zooplankton community. To evaluate the effect of sea ice reduction on zooplankton, we studied year-to-year changes of zooplankton community structure in the Chukchi Sea during summers of 1991, 1992 (when sea ice extended), 2007, and 2008 (when sea ice reduced). Zooplankton abundance ranged from 4,000 to 316,000 ind. m(-2) (mean: 70,000) and was greater north of Lisburne Peninsula in 2008. Zooplankton biomass ranged from 0.07 to 286 g wet mass m(-2) (mean: 36) and was greater south of Lisburne Peninsula in 2007. Cluster analysis based on zooplankton abundance showed a division of the zooplankton community into four groups. Occurrence of each group was separated geographically and interannually, and geographic distributions of each group in 1991 and 1992 were similar but those in 2007 and 2008 were shifted northward. Abundance and biomass in 2007/2008 were higher than in 1991/1992, indicating that further sea ice reduction would have a positive effect on zooplankton production (e.g. invasion of large Pacific species and temperature effects on their growth rate). The northern shift in geographic distribution of the zooplankton community in 2007/2008 indicates that sea ice reduction would have a negative effect on the zooplankton community (loss of characteristic Arctic species) in part of the Chukchi Sea. These apparently contradictory effects of sea ice reduction on zooplankton community emphasize the critical need for continued monitoring in this area.
  • Ken-Ichi Sato, Atsushi Yamaguchi, Hiromichi Ueno, Tsutomu Ikeda
    JOURNAL OF PLANKTON RESEARCH 33 8 1230 - 1238 2011年08月 [査読有り][通常論文]
     
    Fine-scale vertical distribution patterns of the calanoid copepods Neocalanus flemingeri, Neocalanus cristatus, Eucalanus bungii and Metridia pacifica were studied by stratified sampling (9 strata between 0 and 1000 m) with a vertical multiple plankton sampler (VMPS) every 3 h for 24 h during 21-22 March 2005 in the Oyashio region. Most C1-C5 stages of N. flemingeri and N. cristatus occurred in the 30-90 m and 70-200 m strata, respectively, both by day and night. Irrespective of day and night, C3-C6 E. bungii were distributed broadly in the 200-430 m stratum (C5 inhabiting the shallowest layer). Thus, these three copepods exhibited vertical partitioning of their habitats in the upper layers. The C1-C6 of M. pacifica were distributed broadly from 140 to 400 m during daytime and migrated up to the 100-180 m layer at night (except for non-migrant C1 and C6 males). The within-species zonation of copepodid stages was less marked, but older stages tended to occupy deeper zones (N. flemingeri, N. cristatus and M. pacifica) or shallower zones (E. bungii). Gut content analyses of N. flemingeri and N. cristatus revealed the predominance of diatoms in the guts of both species, but the proportion of broken cells was greater in the deep-dwelling N. cristatus than in the shallow-dwelling N. flemingeri, suggesting the importance of sinking phytoplankton aggregates as a food source for the former species.
  • 山口 篤, 花宮 由理佳, 村瀬 弘人, 渡邉 光
    水産海洋研究 75 3 185 - 186 2011年08月01日 [査読無し][通常論文]
  • HOMMA Tomoe, YAMAGUCHI Atsushi, BOWER John R.
    Bulletin of the Fisheries Sciences, Hokkaido University 61 2/3 29 - 47 北海道大学大学院水産科学研究院 2011年 [査読無し][通常論文]
     
    To evaluate vertical changes in the abundance, biomass, and community structure of copepods and their effect on materialflux, stratified samples were collected at 15 discrete depths between 0 and 3,000 m with a fine mesh size (60 μm) Vertical MultiplePlankton Sampler in the southern Bering Sea and northern North Pacific on 14 and 16 June 2006. Both copepod abundanceand biomass decreased with increasing depth, and both decreases were described well with a power model. A total of 72 calanoidcopepod species belonging to 34 genera and 15 families were identified in the Bering Sea and 63 species belonging to 32genera and 13 families were identified in the northern North Pacific. At both stations, the copepod communities comprised fivegroups that had distinct vertical distribution patterns. The groups at 500-1,500 m were adapted to the oxygen minimum zone,and copepod carcasses outnumbered living specimens at 500-750 m in the northern North Pacific and at 750-1,000 m in the BeringSea. Oxygen levels were very low in the minimum zone in both regions, so the occurrence of a specialized community andthe abundance of carcasses are considered to be a special characteristics at these depth. Based on metabolic rates estimated froman empirical equation, copepods were estimated to consume 20±13% (mean±sd) of the particle organic carbon flux throughoutthe water column in the Bering Sea and 32±19% of the flux in the northern North Pacific. The feeding impact of copepods wasestimated to be greatest at 0-100 m. As the fate of POC flux, heterotrophic bacteria was estimated to be important at 100-1,000m, while most of them were considered to be directly sinking a t1,000-3,000 m.
  • 大橋 理恵, 石井 健一郎, 藤木 徹一, 喜多村 稔, 松本 和彦, 本多 牧生, 山口 篤
    日本プランクトン学会報 58 2 123 - 135 日本プランクトン学会 2011年 [査読有り][通常論文]
     
    To evaluate short-term changes in planktonic community, we analysed phytoplanktonand zooplankton collected by a sediment trap moored at 150 m of St. K2 (47°N, 160°E) in the western subarctic Pacific with precision of two-day interval during 7 June to 1 July 2006. Phytoplankton flux varied from 480 to 372,290 cells m^-2 day^-1, and had a peak in 17-19 June. Phytoplankton community was composed of five diatom species and one silicoflagellate species. From Bray-Curtis cluster analysis, phytoplankton communities were classified into four groups. Zooplankton abundance ranged from 1,137 to 3,385 inds. m^-2 day^-1 and showed two peaks in 13-15 June and 21-23 June. Throughout the study period, large copepod Eucalanus bungii accounted 50-90% of total zooplankton abundance. Gonad maturation of adult females of E. bungii advanced during the study period: immature occurred before 15 June, developed during 19-27 June and newly recruited specimens to adult females were observed after 25 June. As carnivorous zooplankton, chaetognath community was predominated by Sagitta elegans (99.7% of total abundance). Body length of S. elegans ranged 22-39 mm, and the mean body length gradually increased during the study period (0.21 mm per day, r^2=0.72, p<0.01). Gonad maturation was also observed from immature stages in early June to mature stages in late June. As a characteristics of short-term changes in planktonic community, phytoplankton abundance fluctuated (max : min=780), while stable for zooplankton abundance (max : min=3). Species composition also greatly varied for phytoplankton than that in zooplankton. For zooplankton, development of juvenile and gonad maturation of adult were observed for both herbivores and carnivores. Thus, short-term changes during early summer of subarctic Pacific were characterized by phytoplankton succession in the abundance and species composition and rapid zooplankton growth in the development and maturity.
  • 大塚 攻, 山口 篤, 花村 幸生
    日本プランクトン学会報 58 1 87 - 93 日本プランクトン学会 2011年 [査読有り][通常論文]
     
    本稿では，動物プランク卜ンとして重要なカイアシ類，アミ類に共生する繊毛虫の生活史，生態，生態的機能について概説する。なお，「共生」に関する厳密な定義は困難である場合があるが(Bush et al. 2001)， ここでは相利共生，片利共生，寄生，捕食寄生，便乗なども含む広義の意味で「共生」という言葉を使用し，宿主と共生生物との種間関係が明確でない場合も「共生」という言葉を使用する。通常，宿主が共生生物より体サイズが大きく，宿主と共生生物間に食関係か成立していて宿主になんらかの悪影響がある場合を「寄生」，宿主を確実に死に至らしめる場合を「捕食寄生」と呼ぶこととする。
  • Rui Saito, Atsushi Yamaguchi, Sei-Ichi Saitoh, Kenshi Kuma, Ichiro Imai
    JOURNAL OF PLANKTON RESEARCH 33 1 145 - 160 2011年01月 [査読有り][通常論文]
     
    The subarctic Pacific is known to have east-west gradients in the oceanic environment and phytoplankton community. The western subarctic Pacific is characterized by low temperature and high chlorophyll a (Chl a) while the eastern region by high temperature and low Chl a. Although there is little information on the differences in the zooplankton community between the eastern and western subarctic Pacific, the gradients in the oceanographic environment and phytoplankton community may markedly affect the zooplankton community in this region. The aim of this study is to clarify east-west differences in the subarctic Pacific zooplankton community. Zooplankton were sampled at stations along the 165 degrees E line (western subarctic Pacific from 41 degrees 30'N to 49 degrees 30'N) and 165 degrees W line (eastern subarctic Pacific from 39 degrees N to 53 degrees 30'N) using 335 and 100 mu m mesh size Twin NORPAC net during the summers of 2003-2006. East-west differences in the zooplankton community were characterized as: (i) greater total zooplankton abundance in the west and (ii) larger body size of calanoid copepods of the same copepodid stage in the west. Differences in east-west zooplankton abundances are attributed to differences in the magnitude of primary production (high in the west) and the size of primary producers (large in the west). Larger body sizes of calanoid copepods in the west are attributed to the lower temperature. Thus, differences in zooplankton abundance and body size are concluded to be due to east-west gradients in the oceanographic environment and phytoplankton community.
  • 北大水産紀要 53 2 13 - 18 2011年 [査読無し][通常論文]
  • YAMAGUCHI Atsushi, OHGI Kohei, KOBARI Toru
    Bulletin of the Fisheries Sciences, Hokkaido University 61 1 13 - 22 北海道大学大学院水産科学研究院 = Research Faculty of Fisheries Sciences, Hokkaido University 2011年 [査読無し][通常論文]
     
    Seasonal sequence of population structure (=copepodid stage composition) of large grazing copepods (Metridia pacifica, Eucalanus bungii and Neocalanus spp.) was analyzed based on seasonal samples collected with 100 μm mesh nets from 0-500 m stratum at Site H in the Oyashio region, western subarctic Pacific, during 1996-1997 and 2002-2007. On the premise that there are little year-to-year differences, the composite data were arranged to the date of samplings of each year to yield seasonal developmental patterns of each copepod. Seasonal developmental pattern estimated by tracing the sequence of mean copepodid stages of the population at each sampling date revealed that the recruitment season of the population was January for N. cristatus, March for N. flemingeri and May for N. plumchrus and E. bungii. In contrast to these copepods with single recruitment seasons in the year, M. pacifica exhibited two recruitment seasons (mid-May and August) in a year. Phenology in reproduction and development of these copepods reflects their species-specific differences in energy utilization pattern ; M. pacifica and E. bungii spawn in phytoplankton-rich surface layer in spring (females need to feed for spawning) while Neocalanus spp. spawn in deep layer in winter (females do not feed). Development from C1 to C5 of N. cristatus, N. flemingeri and N. plumchrus was in January to June, March to June and May to August, respectively, thus the three sympatric Neocalanus spp. showed a clear temporal separation in the developmental timing in the western subarctic Pacific. This temporal separation in utilizing the surface layer is considered to be a mechanism to reduce inter-specific food competition. Regional comparison of phenology in copepods within the entire subarctic Pacific and its adjacent waters revealed that reproduction timing of the surface spawning M. pacifica and E. bungii was highly variable, while this was not the case for deep spawning Neocalanus spp.
  • Hye Seon Kim, Atsushi Yamaguchi, Tsutomu Ikeda
    DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY 57 17-18 1733 - 1741 2010年09月 [査読有り][通常論文]
     
    Rates of oxygen consumption (R: mu l O(2) [individual](-1) h(-1)), and ammonia excretion (E: mu g NH(4)-N [individual](-1) h(-1)), O:N ratios (by atoms) and body water contents (% of wet mass [WM], as an index of lipid accumulation) of Euphausia pacifica and Thysanoessa inspinata were monitored during 9-14 March and 6-30 April 2007, including the onset of the spring phytoplankton bloom in the Oyashio region. Regression analyses revealed that variations in R and E were generally correlated with dry body mass (DM) for both euphausiids. When R and E were standardized to a body size of 10 mg DM, R(std), E(std), O:N ratios and water contents fluctuated from 6.3 to 10.1, 0.07 to 0.34, 31 to 232 and 73.8 to 78.1, respectively, for E. pacifica, and from 8.7 to 11.3, 0.06 to 0.71, 24 to 295 and 75.1 to 82.2, respectively, for T. inspinata. None of these variables were significantly correlated with temporal variations in SST (1.7 to 5.7 degrees C) or chlorophyll a standing stock (29.4 to 252.6 mg m(-2), 0-100 m) at the study site. However, April E and O:N ratio data pooled for both euphausiids were significantly less and greater, respectively, than the pooled values in March, suggesting preferential utilization of dietary protein for body growth or reproduction under conditions of abundant food supply as found in April. No substantial differences were observed in water content, ash, C, N or C:N ratios (by mass) of the two euphausiids collected in either March or April. Water content, C, N, C:N ratio and ash data averaged for E. pacifica and T. inspinata over the March and April cruises were similar: 76.3 and 78.1% of WM, 36.1 and 37.5% of DW, 9.4 and 10.1% of DW, 3.82 and 3.71 by mass, and 10.6 and 10.8% of DM, respectively. Combining the R-DM and E-DM relationships established with the population structure data of Kim et al. (2010), we estimate that daily ingestion and ammonia-N regeneration by the combined populations of the two euphausiids were 1.5-24.1% (integrated mean: 4.9%) and 0.18-1.32% (0.41%), respectively, of primary production and associated N demand during the bloom. Crown Copyright (C) 2010 Published by Elsevier Ltd. All rights reserved.
  • Atsushi Yamaguchi, Yuka Onishi, Momoka Kawai, Aya Omata, Mariko Kaneda, Tsutomu Ikeda
    DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY 57 17-18 1691 - 1702 2010年09月 [査読有り][通常論文]
     
    Short-term changes in vertical distributions of copepods during the spring phytoplankton bloom were analyzed based on day and night vertically stratified sampling (9 strata between 0 and 1000 m) with a fine-mesh (60 mu m) VMPS in the Oyashio region on five occasions: 8 March, 5, 11, 23 and 29 April 2007. Responses to the bloom were varied and species-specific. Eucatanus bungii C3-C6 were resting around 400 m on 8 March. They had aroused from rest by 5 April, more completely for C6F than for C3-C4. On 29 April, newly recruited C1-C4 stayed in near-surface layers (0-50 m). Both Metridia pacifica and Metridia okhotensis showed strong diel vertical migrations (DVM). When the amount of sinking flux was sufficient (23 and 29 April), juveniles ceased DVM and stayed close to 300 m throughout the day and night, while the C6F continued DVM. Continuous DVM behavior of Metridia spp. C6F is likely related to spawning in the surface layer at night. The growth phase of juvenile Neocalanus spp. occurred shallower than 250 m. Within this depth range, vertical partitioning was observed among the species: Neocalanus flemingeri and Neocalanus plumchrus occurred above 50 m, while Neocalanus cristatus was distributed from 75 to 250 m. The boundary between two patterns was around 50-75 m. These findings are comparable to those in the eastern subarctic Pacific. (C) 2010 Elsevier Ltd. All rights reserved.
  • Atsushi Yamaguchi, Yuka Onishi, Aya Omata, Momoka Kawai, Mariko Kaneda, Tsutomu Ikeda
    DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY 57 17-18 1679 - 1690 2010年09月 [査読有り][通常論文]
     
    As a basis for analyzing development of six large grazing copepods (Eucalanus bungii, Metridia pacifica, M. okhotensis, Neocalanus cristatus, N. flemingeri and N. plumchrus) in the Oyashio region, quasi-daily twin-NORPAC net (0.33 and 0.10 mm mesh) hauls were taken through the upper 150 m and 500 m at a station southwest of Hokkaido before (9-14 March) and after (6-30 April) the onset of the phytoplankton bloom in 2007. Based on additional fresh specimens collected from 0-150 m, egg production of E. bungii, M. pacifica and M. okhotensis, and gut pigments of late copepodid stages in each species were evaluated. Total zooplankton biomass was greater from 10 April onward by a factor of 2- to 8-fold the previous levels. This increase of the 0-150 m biomass was caused by development of Neocalanus spp. copepodids and upward migration of resting E. bungii. Egg production of E. bungii peaked on 18 April, while abundance of its nauplii and Cl peaked on 20 and 25 April, respectively. Sex ratio and C6-female gonad maturation index of E. bungii showed new recruitment to C6 during 20-30 April, likely derived from a population that over-wintered as C3 or C4. Egg production and hatchability of M. pacifica and M. okhotensis were highly variable and no temporal trend was detected. Comparison with field abundance data for Metridia spp. suggests that our estimates of egg production and hatchability are too low, despite care with experimental conditions. All the Neocalanus species utilize the bloom as energy for juvenile growth. Neocalanus cristatus developed from C2 through C4, and stage duration of C3 was estimated to be 24 days. Neocalanus flemingeri also developed from Cl through C3, and stage durations of Cl and C2 were estimated to be 7-9 days. Neocalanus plumchrus occurred in small numbers from mid-April onward. The stage duration estimates for Neocalanus spp. are similar to those reported from the high-nutrition southeastern Bering Sea shelf. Gut pigment variation clearly showed nocturnal feeding by Metridia spp., while no diel changes in gut pigment were recognized for E. bungii or Neocalanus spp. The diel changes in gut pigment of Metridia spp. were related to their diel vertical migrations. The calendar of sequential responses of copepods to the phytoplankton bloom is summarized. (C) 2010 Elsevier Ltd. All rights reserved.
  • Tsutomu Ikeda, Atsushi Yamaguchi, Charles B. Miller
    DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY 57 17-18 1593 - 1594 2010年09月 [査読有り][通常論文]
  • Hye Seon Kim, Atsushi Yamaguchi, Tsutomu Ikeda
    DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY 57 17-18 1727 - 1732 2010年09月 [査読有り][通常論文]
     
    The abundance and population structure of Euphausia pacifica and Thysanoessa inspinata were investigated during the period 9 March-29 April 2007 at a single station in the Oyashio region. Water temperature and chlorophyll a concentration varied from 1.1 to 6.1 degrees C and from 0.02 to 6.3 mg m(-3), respectively, primarily reflecting the effects of varying mixtures of the water masses prevailing in this region. The abundance of euphausiids, collected by oblique hauls with Bongo nets (0-200 m) at night, fluctuated from 41 to 1040 individuals m(-2) for E. pacifica and from 50 to 186 individuals m(-2) for T. inspinata. Correlation analyses revealed that the variations in the abundance of E. pacifica were related to water temperature and chlorophyll a, while abundance of T. inspinata only varied with temperature. Adult males and females (with and without spermatophores) were the major components of both euphausiid stocks (> 90% of the total). Modal size (= total length or TL) analysis revealed that one group with large sizes (14-18 mm TL for E. pacifica, 16-18 mm TL for T. inspinata) occurred throughout the study period, often accompanied by one discrete group of smaller individuals (< 11 mm TL for both euphausiids), suggesting the distribution of the same euphausiid populations across the heterogeneous water masses. Adult males were significantly smaller than adult females in T. inspinata, but this was not the case in E. pacifica. Tracing the progressive increase in the mean sizes of the larger size groups, growth rates were estimated to be 0.082 mm day(-1) for E. pacifica and 0.022 mm day(-1) for T. inspinata. The difference in the growth rates of the two euphausiids is discussed in light of species-specific differences in the allocation of energy to reproduction and somatic growth during the present study period. Crown Copyright (C) 2010 Published by Elsevier Ltd. All rights reserved.
  • Tomoe Homma, Atsushi Yamaguchi
    DEEP-SEA RESEARCH PART I-OCEANOGRAPHIC RESEARCH PAPERS 57 8 965 - 977 2010年08月 [査読有り][通常論文]
     
    Vertical changes in abundance, biomass and community structure of copepods down to 3000 m depth were studied at a single station of the Aleutian Basin of the Bering Sea (53-28'N, 177 00'W, depth 3779 m) on the 14th June 2006. Both abundance and biomass of copepods were greatest near the surface layer and decreased with increase in depth. Abundance and biomass of copepods integrated over 0-3000 m were 1,390,000 inds. m(-2) and 5056 mg C m(-2), respectively. Copepod carcasses occurred throughout the layer, and the carcass:living specimen ratio was the greatest in the oxygen minimum layer (750-100 m, the ratio was 2.3). A total of 72 calanoid copepod species belonging to 34 genera and 15 families occurred in the 0-3000 m water column (Cyclopoida. Harpacticoida and Poecilostomatoida were not identified to species level). Cluster analysis separated calanoid copepod communities into 5 groups (A-E). Each group was separated by depth, and the depth range of each group was at 0-75 m (A), 75-500 m (B), 500-750 m (C), 750-1500 m (D) and 1500-3000 m (E). Copepods were divided into four types based on the feeding pattern: suspension feeders, suspension feeders in diapause, detritivores and carnivores. In terms of abundance the most dominant group was suspension feeders (mainly Cyclopoida) in the epipelagic zone, and detritivores (mainly Poecilostomatoida) were dominant in the meso- and bathypelagic zones. In terms of biomass, suspension feeders in diapause (calanoid copepods Neocalanus spp. and Eucalanus bungii) were the major component (ca. 10-45%), especially in the 250-3000 m depth. These results are compared with the previous studies in the same region and that down to greater depths in the worldwide oceans. (C) 2010 Elsevier Ltd. All rights reserved.
  • 福井 大介, 北辻 さほ, 池田 勉, 志賀 直信, 山口 篤
    日本プランクトン学会報 57 1 30 - 40 日本プランクトン学会 2010年02月 [査読有り][通常論文]
     
    地球温暖化の海洋生態系へ与える影響を理解する手段のひとつとして、歴史的資料を用いた気候変動と海洋構造の変化、それに伴う生物群集の応答についての長期モニタリングと解析が世界の様々な海域で現在行われている。北海道西部の日本海に面した石狩湾南西部に位置する忍路湾では、1947年から2004年まで長期にわたって定期的な海洋観測と植物プランクトン採集が行なわれ、その一部はすでに報告されている。本研究ではこれらの長期連続採集試料のうち、1984-2004年（21年間）の試料を用いて、植物プランクトンの種査定と細胞数密度の算出を行い、現存量（細胞数密度）と群集構造の長期変動と同湾の環境要因との関係を明らかにすることを目的とした。
  • Kohei Matsuno, Atsushi Yamaguchi
    Plankton and Benthos Research 5 4 123 - 130 2010年 [査読有り][通常論文]
     
    Zooplankton abundance and biomass along 165°E and 165°W in the North Pacific were estimated using an optical plankton counter on preserved samples collected with a plankton net of 335μ m mesh-size from 0-150 m at 89 stations from the subarctic to subtropical regions during the summers of 2003-2006 the stations were grouped into subarctic (SA), transitional (TR) and subtropical (ST) regions for latitudinal comparisons. The two-way ANOVA and a post hoc test showed that total abundance and biomass were significantly larger in SA and smaller in ST stations, respectively, than in the other regions, but were not significantly different between 165°E and 165°W. Total ranges of abundance and biomass were: 34×103-65×103 indiv. m-2 and 2.9-7.9 g dry mass m-2, respectively. The variation in abundance was mainly governed by the variation of 0.34-1.00 mm equivalent spherical diameter (ESD) size class zooplankton, but total biomass variations were due mainly to the 2.00-3.00 mm ESD size class, which corresponds to the calanoid copepod Neocalanus spp. copepodid stage 5 (C5) that had a greater abundance in SA and TR than in ST. Despite possibly higher abundances of Neocalanus C5 in TR than in SA, abundance and biomass of the 2.00-3.00mm ESD size class were not significantly different between the two regions. Size reduction of individuals due to higher temperatures in TR than in SA may be a possible explanation. © The Plankton Society of Japan.
  • Kim Hye Seon, Yamaguchi Atsushi
    Bulletin of the Fisheries Sciences, Hokkaido University 60 1 13 - 18 北海道大学大学院水産科学研究院 = Research Faculty of Fisheries Sciences, Hokkaido University 2010年 [査読無し][通常論文]
     
    This paper presents the first data on the early larval morphology of euphausiid Thysanoessa inspinata and T. longipes. Female animals were captured in the Oyashio region during May 2006 and investigated through a 31 day period in a laboratory experiment. Between 76-142 eggs were found to be released from Thysanoessa inspinata during each spawning (hatching success=81-99%) and 136 eggs (hatching success=65%) were released from the T. longipes females. The morphology of T. inspinata and T. longipes during all stages as eggs, Nauplius I, II and Metanauplius larvae were similar, but distinguished significantly by size (T. inspinata
  • Kohei Matsuno, Hye Seon Kim, Atsushi Yamaguchi
    Plankton and Benthos Research 4 4 154 - 159 2009年 [査読有り][通常論文]
     
    Size-fractionated (0.25, 0.5, 1, 2, and 4 mm mesh size) wet mass (WM) and dry mass (DM) determinations and optical plankton counter (OPC) measurements were carried out on zooplankton samples collected at 15 stations in the northern North Pacific Ocean, Bering Sea and Chukchi Sea during July-August 2007. The total sampleWM and DM estimated from OPC data corresponded closely to those of measured values by a factor of 0.970-1.098. However when the sample was portioned into different size groups, estimates of size-fractionated WM and DM by OPC data varied from measured masses by a factor of between 0.202 and 1.768. The high variability was caused by an underestimation of sizes of the large sized (< mm) fraction, or an overestimation of the number of the small size fraction (2-4 mm). The underestimation in the < mm and overestimation in the 2-4 mm respectively were caused by the dominance of transparent hydromedusae, and slender-shaped euphausiids in the < mm fraction. This study suggests that OPC analysis could be susceptible to errors in zooplankton biomass estimates in the large size fraction (< mm) especially when euphausiids and hydromedusae dominate the population. On the other hand, OPC based estimates of DM within 0.25-4 mm size fraction are more robust, which may be due to the dominance of large copepods, and low detritus content in the samples from the oceanic subarctic Pacific, in summer 2007. © 2009, The Plankton Society of Japan, The Japanese Association of Benthology. All rights reserved.
  • Hye Seon Kim, Atsushi Yamaguchi, Tsutomu Ikeda
    Plankton and Benthos Research 4 2 43 - 52 2009年 [査読有り][通常論文]
     
    A series of oblique hauls with Bongo nets (0-1000m) was made during the period of August 2002 through August 2004 in the Oyashio region, western subarctic Pacific, to investigate abundance, biomass and life cycle patterns of the three predominant euphausiids (Euphausia pacifica, Thysanoessa inspinata and T. longipes). While the three euphausiids occurred throughout the entire study period, E. pacifica was the most abundant (1,120indiv.m 2, or 832mgCm 2), followed by T. inspinata (163indiv.m 2, or 144mgCm 2) and T. longipes (73indiv.m 2, or 75 mgCm 2). Judging from the occurrence of females with spermatophores and furcilia larvae, the spawning was consid-ered to take place twice a year (April-May and August) for E. pacifica, year-round (peak season: March-May) for T. inspinata and in spring (March-May) for T. longipes. The population structure in terms of size (total length) fre- quency distributions of the three euphausiids was characterized by the frequent co-occurrence of 2-3 cohorts in the same samples. The maximum size of males and females found were 21mm and 24mm, respectively, for E. pacifica, 18mm and 23mm, respectively, for T. inspinata, 27mm and 31mm, respectively, for T. longipes. Tracing the sequence of cohorts, the life spans of E. pacifica, T. inspinata and T. longipes were estimated to be 17-26 months, 17-19 months and 29-31 months, respectively. These results are compared with reports of the same species in other habitats in the light of regional variations. © The Plankton Society of Japan.
  • OHTSUKA Susumu, HANAMURA Yukio, HORIGUCHI Takeo, YAMAGUCHI Atsushi, SHIMOMURA Michitaka, SUZAKI Toshinobu
    日本甲殻類学会大会講演要旨集 47th 36  2009年 [査読無し][通常論文]
  • Yasuhiro Takenaka, Hiromi Masuda, Atsushi Yamaguchi, Satoshi Nishikawa, Yasushi Shigeri, Yasukazu Yoshida, Hiroshi Mizuno
    GENE 425 1-2 28 - 35 2008年12月 [査読有り][通常論文]
     
    We cloned two forms of the secreted and thermostable luciferase genes, MpLuc1 and MpLuc2, from the marine copepod, Metridia pacifica. The 840-bp MpLuc1 cDNA comprised a 630-bp open reading frame encoding a 210-amino acid polypeptide (22.7 kDa). MpLuc1 had the closest homology with Metridia longa luciferase. The 753-bp MpLuc2 cDNA consisted of a 567-bp open reading frame (20.3 kDa), and it had the closest homology with Gaussia princeps luciferase. Single-specimen genomic PCR confirmed the presence of two luciferase genes in M. pacifica, and single-specimen RT-PCR revealed that both luciferase mRNAs were expressed. Both MpLuc1 and MpLuc2 (MpLucs) specifically reacted with the substrate coelenterazine producing identical bioluminescent spectra (lambda max, 485 nm), but with different kinetics. Adding salt such as MgCl2 and CaCl2 to the reaction mixture significantly enhanced MpLuc1 and MpLuc2 activities. Wild-type MpLucs were remarkably thermostable; MpLuc1 retained about 60% of the original activity even after incubation at 90 degrees C for 30 min. MpLucs expressed in NIH-3T3 and HeLa cells were largely secreted into the culture medium. Continuous monitoring of secreted MpLuc1 driven by the c-fos promoter demonstrated the potential usefulness of MpLuc1 in nondisruptive reporter assays. (c) 2008 Elsevier B.V. All rights reserved.
  • Padmini Dalpadado, Atsushi Yamaguchi, Bjornar Ellertsen, Signe Johannessen
    DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY 55 20-21 2266 - 2274 2008年10月 [査読有り][通常論文]
     
    The diets of krill and amphipods were examined using light microscopy on field-collected specimens from 2004 to 2005 from the Marginal Ice Zone of the northwestern Barents Sea, north and east of Spitsbergen. Stomach content analyses indicate dominant krill species to have a filter-feeding mode, whereas amphipods seem to be mainly raptorial feeders. The dominant krill, Thysanoessa inermis, is primarily regarded as an herbivore feeding mostly on diatoms. Alternatively, Thysanoessa longicaudata fed occasionally on calanoid copepods in addition to being a suspension feeder on phytoplankton. The largest of the krill species, Meganyctiphanes norvegica, showed a mixed diet with regular feeding on calanoid copepods and phytoplankton. The degree of carnivory varied between stations and was determined by examining the size and shape of the mandible of copepods. M. norvegica, with a total length of between 26 and 41 mm, had up to two copepods in their stomachs, with a mandible width of the copepods varying from 32 to 154 mu m, corresponding, respectively, to a computed prosome length of 0.3 and 2.6 mm, Themisto libellula fed primarily on C3 and C4 copepodite stages of Calanus glacialis and Calanus hyperboreus, and up to three copepods were found in the stomach contents of T libellula. Themisto abyssorum fed on herbivorous and omnivorous prey such as copepods and appendicularians. The presence of Metridia spp. and appendicularians, e.g., Oikopleura vanhoeffeni in the diet of T abyssorum may indicate feeding in the deeper layers (>200 m). (C) 2008 Elsevier Ltd. All rights reserved.
  • 山口 篤, 渡辺 雄二, 石坂 丞二
    海洋 40 6 349 - 361 海洋出版 2008年08月 [査読無し][通常論文]
     
    海洋中・深層におけるプランクトン群集構造と彼らの生命活動による物質収支を明らかにすることは，海洋における物質循環を評価する上で重要である.本稿では西部北太平洋の4定点における表層から水深5800m におよぶ深層までのプランクトンバイオマスとその群集構造について紹介し，深海生態系の食物網構造について考察を行う.深海でもマイクロバイアルループ(沈降POC-DOC-従属栄養バクテリアー鞭毛虫-渦鞭毛虫)は駆動するものの多細胞動物プランクトンの餌としては表層動物プランクトンからの沈降糞粒などの方がより重要であることが示された.
  • Tsutomu Ikeda, Naonobu Shiga, Atsushi Yamaguchi
    JOURNAL OF OCEANOGRAPHY 64 3 339 - 354 2008年06月 [査読有り][通常論文]
     
    Biomass distribution and trophodynamics in the oceanic ecosystem in the Oyashio region are presented and analyzed, combining the seasonal data for plankton and micronekton collected at Site H since 1996 with data for nekton and other animals at higher trophic levels from various sources. The total biomass of biological components including bacteria, phytoplankton, microzooplankton, mesozooplankton, micronekton, fishes/squids and marine birds/mammals was 23 g C m(-2), among which the most dominant component was mesozooplankton (34% of the total), followed by phytoplankton (28%), bacteria (15%) and microzooplankton (protozoans) (14%). The remainder (9%) was largely composed of micronekton and fish/squid. Marine mammals/birds are only a small fraction (0.14%) of the total biomass. Large/medium grazing copepods (Neocalaus spp., Eucalanus bungii and Metridia spp.) accounted for 77% of the mesozooplankton biomass. Based on information about diet composition, predators were assigned broadly into mean trophic level 3-4, and carbon flow through the grazing food chain was established based on the estimated annual production/food consumption balance of each trophic level. From the food chain scheme, ecological efficiencies as high as 24% were calculated for the primary/secondary production and 21% for the secondary/tertiary production. Biomass and production of bacteria were estimated as 1/10 of the respective values for phytoplankton at Site H, but the role of the microbial food chain remains unresolved in the present analysis. As keystone species in the oceanic Oyashio region, Neocalanus spp. are suggested as a vital link between primary production and production of pelagic fishes, mammals and birds.
  • 横井 裕, 山口 篤, 池田 勉
    日本プランクトン学会報 55 1 9 - 24 日本プランクトン学会 2008年02月 [査読有り][通常論文]
     
    The abundance, biomass and size structure of mesozooplankton samples collected with Norpac nets from 0-150 m at 5-l3 latitudinal stations (35°N to 44°N) on 155°E in the western North Pacific annually during May-June (1993-2004) were analyzed using an optical plankton counter. Zooplankton counts of 4096 size units (size range: 0.25 to 20 mm equivalent spherical diameter [ESD]) were converted to biomass and summed as the community biomass. Data of each size class were combined with in situ water temperature data to estimate production potential. Based on the latitude, the study region was classified into subarctic front (SF:＞42°N), transition domain (TR: 40-42°N), subarctic boundary (SB: 38-40°N) and subtropic current system (ST: ＜38°N). Throughout the study period, regional variations were seen in most size fractions in abundance (52,754-86,926 inds. m^-2), biomass (2,656-10,183 mg dry mass m^-2), and production (134-219 mg C m^-2d^-1). The TR was characterized by high biomass and production, but it had the lowest abundance. Interannual variations in abundance, biomass and production were largely due to variation in the 2-3 mm ESD fraction. Thus, the 2-3 mm ESD fraction (composed of Neocalanus spp.) was the most important one affecting not only the regional but interannual variation patterns of mesozooplankton. Apart from the consistent importance of Neocalanus spp., gelatinous zooplankton such as appendicularians, doliolids and salps were observed to form irregular peaks in the ST and SB regions in some years. It is suggested that the outbreaks of gelatinous zooplankton were related to the development of the thermocline or halocline in the top 40 m of the water column, which may stop the nutrient supply to the surface layer and increase the food supply via the microbial loop.
  • Miho Ozawa, Atsushi Yamaguchi, Tsutomu Ikeda, Yuji Watanabe, Joji Ishizaka
    Plankton and Benthos Research 2 4 184 - 197 2007年11月 [査読有り][通常論文]
     
    Abundance and community structure of chaetognaths were studied based on the vertical stratified zooplankton samples from the epipelagic through abyssopelagic zones (maximum: 5,000-5,800 m) at four stations in the western North Pacific (44°N, 39°N, 30°N, and 25°N) and one station each in the Japan Sea, Okhotsk Sea, and Bering Sea. Chaetognath standing stocks (indiv. m-2) were greatest at subarctic stations (44°N, Okhotsk Sea, and Bering Sea). Vertically, chaetognath density (indiv. m-3) was the greatest in the shallowest depths, and decreased with increasing depth. Chaetognaths occurred down to 4,000-5,000 m at subarctic stations, while chaetognaths were not found below 3,000 m at subtropical stations (30°N and 25°N). The number of chaetognath species was the greatest (22 representing 14 genera) at the transition station (39°N), and the least (1 species) at the station in the Japan Sea. Species diversity indices (H′) were low at subarctic stations, but high at subtropical stations. Vertical profiles of H′ varied also between these stations it peaked at the mesopelagic zone at subarctic stations, and at the epipelagic zone at subtropical stations. Cluster analysis separated chaetognath communities of the study region into 5 groups (A-E) characterized by discrete spatial distribution: group A the mesopelagic zone at subtropical and transition areas, group B the epipelagic zone at subtropical and transition areas, group C the bathy- and abyssopelagic zone (except the Japan Sea), group D all depths in the Japan Sea, and group E the epi- and mesopelagic zones in the subarctic area. For the four most abundant species at the subarctic stations, allometric data showed greater head width to total length ratios, and greater hook length to total length ratios for deeper-dwelling species. Relatively larger head width (i.e. large mouth) and longer hooks of deep-sea chaetognaths are considered to be an adaptation significant to the successful capture of prey zooplankton in resource limited deep-sea environments. © The Plankton Society of Japan.
  • 山口 篤
    海の研究 16 2 129 - 142 日本海洋学会 2007年03月05日 [査読無し][通常論文]
     
    西部北太平洋の亜寒帯域から亜熱帯域におよぶ4定点において,水深5,800mにまでおよぶ全プランクトン分類群のバイオマスを明らかにした。深度増加に伴うバイオマスの減衰度合いは分類群によって異なり,この差は各分類群の栄養生態に起因するものと考えられた。亜寒帯域では多細胞動物プランクトンの占有率が高く,亜熱帯域では従属栄養バクテリアと単細胞動物プランクトンの占有率が高かった。亜寒帯域における主要分類群であるカイアシ類の生態学的特徴を調査研究して,同属の種間で鉛直分布を変えて棲み分けしていることや,多くの中・深層性カイアシ類が若い発育段階では深い層に分布し,発育に伴う鉛直移動をすることを明らかにした。また中・深層性種の生活史の再生産時期は表層で植物プランクトンブルームのある時期に同調しており,これは表層からの沈降粒子輸送量の増加に関係したものと考えられた。西部北太平洋亜寒帯域の全水柱を通して,カイアシ類は有機炭素輸送量の32%を消費すると推定された。
  • Tsutomu Ikeda, Fumikazu Sano, Atsushi Yamaguchi, Takashi Matsuishi
    AQUATIC BIOLOGY 1 2 99 - 108 2007年 [査読有り][通常論文]
     
    As indices of protein synthetic activity, RNA:DNA ratios were determined for > 80 copepod species caught from the epipelagic (0 to 500 m), mesopelagic (500 to 1000 m), upper bathypelagic (1000 to 2000 m), lower bathypelagic (2000 to 3000 m) and abyssopelagic (3000 to 5000 m) zones of the North Pacific Ocean. The copepods from the epipelagic zone exhibited higher RNA:DNA ratios compared to those from the mesopelagic through the abyssopelagic zones. Parameters (,other than the depth zones) affecting the ratios were explored, by grouping the copepods into 4 developmentalstage/sex categories (C4, C5 and C6 females and males), 3 feeding types (carnivore, detritivore and suspension feeder), or 2 phylogeny-related reaction-speed groups in which detecting the presence or absence of myelinated sheath enveloping axons indicated fast or slow reacting species, respectively. Stage and sex data showed that RNA:DNA ratios were greater in C6 females than in other groups. Among the feeding-type data, carnivores exhibited the lowest RNA:DNA values. Reaction-speed data indicated that slow-reacting species are characterized by lower ratios than fast-reacting species. Taking into account all of these biological parameters as independent variables, stepwise multiple regression analysis revealed that the pattern of the reduction in RNA:DNA ratios toward greater depths was still valid. The typical interzonal copepods, Neocalanus spp., showed that non-feeding C6 females of N. plumchrus and N. flemingeri collected from the mesopelagic through the abyssopelagic zones had high RNA:DNA ratios comparable to those of the epipelagic-zone copepods. The present results, combined with recent reports on the depth-related decline in the metabolism and body nitrogen content of pelagic copepods downward, suggest overall slower life modes of deeper-living species. We think the 'predation-mediated selection' hypothesis explains this 'slow' life more effectively than limited food supply or colder temperatures in the deep sea.
  • La mer 45 47 - 58 2007年 [査読有り][通常論文]
  • Tsutomu Ikeda, Fumikazu Sano, Atsushi Yamaguchi
    MARINE ECOLOGY PROGRESS SERIES 339 215 - 219 2007年 [査読有り][通常論文]
     
    Historical global respiration datasets of epipelagic copepods and recent bathymetric respiration datasets of mesopelagic, upper- and lower-bathypelagic and abyssopelagic copepods were combined to build a global-bathymetric respiration model by adopting 2 regression models (theoretical and empirical ones). Designated independent variables including body mass (expressed as dry mass, carbon or nitrogen), habitat temperature, ambient oxygen saturation and the depth of occurrence were all significant, accounting for 72 to 80% in the variation in these respiration data. Both theoretical and empirical regression models yielded similar results, but the latter was sensitive to the choice of body mass. The mechanisms leading to a negative effect of depth and a positive effect of oxygen saturation on respiration rates are thought to be due to 'predation-mediated selection' and the lack of specialized respiratory organs (i.e. oxygen diffusion through the body surface), respectively.
  • Tsutomu Ikeda, Atsushi Yamaguchi, Takashi Matsuishi
    DEEP-SEA RESEARCH PART I-OCEANOGRAPHIC RESEARCH PAPERS 53 11 1791 - 1809 2006年11月 [査読有り][通常論文]
     
    Condition factor index [CFI = 1000 x DW/(PL)(3); DW: dry weight, PL: prosome length], water content, carbon (C), nitrogen (N), ash and energy content were determined on a total of 69 copepod species caught from the mesopelagic (500-1000m), upper-bathypelagic (1000-2000m), lower-bathypelagic (2000-3000m) and abyssopelagic (3000-5000m) zones of the western subarctic Pacific. Resultant data were grouped into these four sampling zones, four developmental stage/sex categories (C4, C5 and C6 females and males), three feeding types (carnivore, detritivore and suspension feeder), or two reaction speed groups by the presence/absence of myelinated sheath enveloping axons (fast and slow reacting species). Zone-structured data showed the overall ranges were 3.8-4.6 mm for PL, 1.6-2.6 mg for DW, 21.4-25.0 for CFI, 75.0-78.6% of wet weight (WW) for water, 51.3-53.7% of DW for C, 7.7-8.8% of DW for N, 6.2-7.0 (by weight) for C/N, 6.9-9.6% of DW for ash and 25.3-27.4 J mg(-1) DW for energy. Among these components, N and ash exhibited significant between-zone differences characterized by gradual decrease downward for the former, and only the upper-bathypelagic zone > abyssopelagic zone for the latter. Stage/sex-structured data showed no significant differences among them, but energy content of C5 was higher than that of C6 females. From the analyses of feeding type-structured data, carnivores were shown to have lower water, N, ash, but higher C, C/N and energy contents than suspension feeders do. Reaction speed-structured data indicated that slow-reacting species have significantly higher water but lower CFL C, N and energy contents than fast-reacting species. Designating these grouping criteria, PL and DW as independent variables, the attributes of these variables to the CFI, chemical composition or energy contents were evaluated by stepwise-multiple regression analysis, showing the most pronounced effect of suspension-feeder, followed by the presence of myelinated sheath, DW, C6 females and the abyssopelagic zone. Further analysis of zone-structured data, by adding epipelagic copepod data from identical thermal habitats (Arctic/Antarctic waters), revealed a more marked decline in N content from the epipelagic zone to the abyssopelagic zone, accompanied by an increase in C/N ratios downward. The decline in N ( = protein or muscle) contents with depth cannot be explained by the "visual interactions" hypotheses being proposed for the metabolism of pelagic visual predators, but is consistent with the "predation-.mediated selection" hypothesis for the metabolism of pelagic copepods. (c) 2006 Elsevier Ltd. All rights reserved.
  • H Masuda, Y Takenaka, A Yamaguchi, S Nishikawa, H Mizuno
    GENE 372 18 - 25 2006年05月 [査読有り][通常論文]
     
    A crustacean gene, encoding for a new class of GFP-like protein, has been isolated from a cDNA library of the deep-sea (benthic) copepod crustacean, Chiridius poppei, by expression cloning. The cDNA library was constructed in a pBluescript II vector and screened using a non-UV transilluminator, obtaining a positive clone. The clone consisted of a 781 -bp fragment of cDNA with a 660-bp open reading frame, which encoded for a 219-amino acid polypeptide with a calculated molecular mass of 24.7 kDa. The protein was overexpressed in Escherichia coli, purified to homogeneity by anion-exchange and size-exclusion chromatographies. The protein, CpYGFP, had excitation and emission maxima at 507 and 517 nm, respectively. CpYGFP existed as a dimer in solution and could be expressed either alone or as a fusion protein in HeLa cells. Dual labeling experiments carried out with CpYGFP-actin and DsRed2-Nuc demonstrated the usefulness of CpYGFP as a reporter in the subcellular localization of actin. (c) 2006 Elsevier B.V. All rights reserved.
  • Y Watanabe, A Yamaguchi, H Ishidai, T Harimoto, S Suzuki, Y Sekido, T Ikeda, Y Shirayama, M Mac Takashi, T Ohsumi, J Ishizaka
    JOURNAL OF OCEANOGRAPHY 62 2 185 - 196 2006年04月 [査読有り][通常論文]
     
    The first CO2 exposure experiments on several species of pelagic copepods inhabiting surface and deep layers in the western North Pacific were conducted. Living organisms were collected from two layers between the surface and 1,500 m between latitudes of 11 and 44 degrees N, and they were exposed aboard ship to various pCO(2) up to about 98,000 mu atm. Mortality of copepods from both shallow and deep layers in subarctic to subtropical regions increased with increasing pCO(2) and exposure time. Deep-living copepods showed higher tolerance to pCO(2) than shallow-living copepods. Furthermore, deep-living copepods from subarctic and transitional regions had higher tolerances than the subtropical copepods. The higher tolerances of the deep-living copepods from subarctic and transitional regions may be due to the adaptation to the natural pCO(2) conditions in the subarctic ocean.
  • 山口篤
    日本プランクトン学会報 53 1 29 - 36 2006年02月 [査読有り][通常論文]
  • Tsutomu Ikeda, Fumikazu Sano, Atsushi Yamaguchi, Takashi Matsuishi
    MARINE ECOLOGY PROGRESS SERIES 322 199 - 211 2006年 [査読有り][通常論文]
     
    Respiration (= oxygen consumption) rates and electron transport system (ETS) enzyme activities in conjunction with body carbon and nitrogen composition (for respiration) or protein (for ETS) were determined for over 50 copepod species from the mesopelagic (M; 500 to 1000 m), upper-bathypelagic (UB; 1000 to 2000 m) and lower-bathypelagic (LB; 2000 to 3000 m) zones of the western subarctic Pacific. Calculated specific respiration rates (SR, a fraction of body carbon respired) at in situ temperatures (3, 2 and 1.5 degrees C for the M, UB and LB zones, respectively) were greater for the M zone copepods (mean: 1.1% body C d(-1)) than that for the UB and LB zone copepods (both 0.6% body C d(-1)). Respiration rates adjusted to those at 1 degrees C by using a Q(10) value (2.0), and to those of specimens with 1 mg body nitrogen by using a body mass exponent (0.8) (e.g. adjusted metabolic rates, AMR, in mu l O-2 (mg body N)(-0.8) h(-1)) were also greater for the M zone copepods than for the UB and LB zone copepods. ETS activities, measured as mu l O-2 (Mg protein)(-0.8) h(-1), showed the same depth-related decline from the M zone to the LB zone. Stepwise regression analysis revealed that stage/sex, feeding type and/or reaction speeds (as judged by the presence/absence of myelin sheath enveloping axons) of copepods were possible additional variables affecting their respiration rates and ETS activities. The reduction in respiration rates and ETS activities from the M zone to the UB or LB zone is more pronounced when respiration rate data on Arctic/Antarctic epipelagic copepods is added; the same is true for ETS activities when respiration rate data is added from copepods dominant in the subarctic Pacific. The present results are compared with those of micronektonic crustaceans and fishes reported for specimens collected from 500 to 2000 m in other regions and discussed in the light of the 'visual interactions' hypothesis.
  • 山口 篤, 志賀 直信, 池田 勉
    海洋 37 8 596 - 604 海洋出版 2005年08月 [査読無し][通常論文]
     
    北太平洋亜寒帯域における浮魚類の餌としての動物プランクトンの資源変動パターンを明らかにするために(1) 動物プランクトンバイオマスの経年変動， (2) 動物プランクトン群集構造の年変動，(3) 表層性魚類資源と動物プランクトンの関係という3点に注目して解析を行った.夏季の亜寒帯域ではまずプランクトン食性小型魚類が亜熱帯域から北上・摂餌回避し次いでシマガツオやアカイカといった魚食性魚類が加わることにより，低次生産物をよりスムーズに高次生物に伝達する生態系構造ができあがると考えられる.
  • A Yamaguchi, S Tachibana, K Hirakawa, T Ikeda
    CRUSTACEANA 78 819 - 837 2005年07月 [査読有り][通常論文]
     
    Based on specimens collected from the Japan Sea, all copepodid stages of the mesopelagic copepod, Gaetanus variabilis are described and illustrated. Among the family Aetideidae, the development of the body segmentation and of the segmentation of the swimming legs in G. variabilis is more similar to that in Gaetanus kruppii than to that in Aetideopsis armata, Chiridius gracifis, or Euchirella messinensis. A sharp, spine-like crest on the frontal dorsal surface of the cephalothorax is a characteristic feature of copepodid stages II-IV of G. variabilis. This frontal crest of G. variabilis, lost in copepodid stages V-VI, is considered as "convergent morphology", relative to G. kruppii. Nucleotide sequences of the mitochondrial 16S rRNA gene confirmed that copepodid stages 11 and III with frontal crest and copepodid stage VI without frontal crest are the same species: Gaetanus variabilis. In the adult male, the mandible, maxillule, and maxilla degenerate, whence no feeding takes place: a phenomenon commonly seen in aetideid copepods.
  • S Shoden, T Ikeda, A Yamaguchi
    MARINE BIOLOGY 146 3 497 - 511 2005年02月 [査読有り][通常論文]
     
    Vertical distribution and population structure of Eucalanus bungii were investigated at site H in the Oyashio region (western subarctic Pacific) from September 1996 through October 1997 to evaluate the species' lifecycle pattern and associated ontogenetic vertical migration. Additional temporary samplings were also made at several stations covering the entire subarctic Pacific, Okhotsk Sea and Japan Sea, as a basis for regional comparison of lifecycle features of this species. At site H, a marked phytoplankton bloom occurred from mid-March to June, and E. bungii spawned in April/May in the surface layer. Resulting nauplii and copepodite stage 1 (C1) formed a prominent abundance peak in early June. The C1 developed and reached C5 by August. The development of nauplii through C4 occurred in the surface layer. From August onwards, C5 and a small fraction of C3-C4 sank gradually deeper, and entered diapause to overwinter at >500 m depth. The C5 molted to C6 males and females in February and March, respectively. The C6 males and females mated at 250-500 m depth, and only mated C6 females ascended to the surface layer in April for spawning. Judging from the size of lipid droplets in the body, the C3-C5 specimens deposited lipids in the body through the phytoplankton bloom period, and the lipids were consumed gradually during overwintering. Taking account of sampling season, temporal changes in population structure, and vertical distribution, the data collected from the western subarctic Pacific and Okhotsk Sea are consistent with a 1-year lifecycle for the site H population, while the data from the central and eastern subarctic Pacific were consistent with a 2-year lifecycle. The populations from the southern and southeastern Japan Sea did not fit the features of either lifecycle scenario, and because of their very small population size it is suggested that they originated from the northern Japan Sea. Regional comparison of the prosome length of C6 females, including those in the Bering Sea, indicated significantly larger specimens from the Japan Sea and Okhotsk Sea, and smaller specimens in the eastern subarctic Pacific, as compared with those in the western subarctic Pacific (including site H) and Bering Sea. A possible overwintering mechanism of E. bungii is discussed.
  • A Yamaguchi, Y Watanabe, H Ishida, T Harimoto, M Maeda, J Ishizaka, T Ikeda, MM Takahashi
    DEEP-SEA RESEARCH PART I-OCEANOGRAPHIC RESEARCH PAPERS 52 2 341 - 353 2005年02月 [査読有り][通常論文]
     
    As part of the research program Western Pacific Environment Study on CO(2) Ocean Sequestration for Mitigation of Climate Change (WEST-COSMIC), plankton sampling was carried out down to great depths (maximum: 5800 m) at four stations (44degreesN, 155degreesE; 39degreesN, 147degreesE; 30degreesN, 147degreesE and 25degreesN, 137degreesE) located in the western North Pacific Ocean. Ranges of plankton standing stock integrated over the water columns were wet mass (WM) 22-256 g m(-2), dry mass (DM) 1.3-27.4 g m(-2), carbon (C) 0.4-12.3 g C m(-2), nitrogen (N) 0.10-2.44 g N m(-2), ash (ash) 0.43-4.35 g m(-2), ash-free dry mass (AFDM) 0.9-21.8 g m(-2) and energy 20-582 kJ m(-2). Log-linear equations were computed to allow interconversions among measurements in different mass units. Plankton mass was greater at higher latitudes. At each station, plankton mass decreased exponentially with increasing depth. This decrease was greater at subarctic each station. (44degreesN) and subtropical (30degreesN and 25degreesN) stations than that at the transitional station (39degreesN) due to high amounts of diapausing copepods in meso- and bathypelagic depths at the latter station. Water content (% of WM), C:N ratios and ash (% of DM) increased with increasing depth, while C, N, AFDM (% of DM) and energy contents (J mg(-1) DM) showed an opposite pattern. Extremely low C (24-25% of DM), N (3.2-4.4% of DM), AFDM (48-56% of DM) and energy contents (10-12 J mg(-1) DM), accompanied by high C:N ratios (5.7-8.0 by weight), of plankton samples from depths below 3000 m suggest possible dominance of detritus in samples from that layer. The overall effect of detritus in measuring chemical composition of plankton samples is discussed. (C) 2004 Elsevier Ltd. All rights reserved.
  • 小澤 美穂, 山口 篤, 喜多村 稔
    北海道大学水産科学研究彙報 55 3 145 - 150 北海道大学大学院水産科学研究科 = GRADUATE SCHOOL OF FISHERIES SCIENCES, HOKKAIDO UNIVERSITY 2004年12月 [査読無し][通常論文]
  • 山口 篤, 目黒 敏美, 梶原 善之, 高木 省吾, 亀井 佳彦, 坂岡 桂一郎
    水産海洋研究 68 4 269 - 269 2004年11月10日 [査読無し][通常論文]
  • T Ikeda, F Sano, A Yamaguchi
    MARINE BIOLOGY 145 6 1181 - 1190 2004年11月 [査読有り][通常論文]
     
    Metabolism [ respiratory oxygen consumption, electron-transfer-system (ETS) activity] and body composition [ water, ash, carbon ( C), nitrogen (N), carbon/ nitrogen (C/N) ratio] of stage C5/C6 Neocalanus cristatus from 1000 to 2000 m depth of the Oyashio region, western subarctic Pacific, were determined during the period of July 2000 through June 2003. Compared with the C5 specimens from shallow depths (< 250 m), those from 1000 to 2000 m were characterized by quiescent behavior, reduced respiration rates (30% of the rates at active feeding), very low water content ( 61 - 70% of wet weight), but high C content ( 56 - 64% of dry weight) and C/N ratios (7.2 - 10.6, by weight). Artifacts due to the recovery of live specimens from the bathypelagic zone appeared to be unlikely in this study, as judged by the consistent results between re-compression ( 100 atm) and non-compression ( 1 atm) respiration experiments, and between ETS activities and respiration rates directly measured. In addition, the respiration rates of C6 males and females of N. cristatus from the same 1000 - 2000 m depth were two to three times higher than the rates of C5 individuals, but were similar to the rates of a bathypelagic copepod, Paraeuchaeta rubra. Combining these results with literature data, C budgets of: ( 1) diapausing C5 specimens, weighing 6 - 10 mg dry weight; ( 2) molt to C6 females; and ( 3) the complete the life span were established, taking into account assorted losses in respiration during diapause at stages C5 and C6, molt production and egg production. Respiratory C losses by C5 and C6 specimens were estimated on the basis of body N as adjusted metabolic rates [AMR; μl O-2 (mg body N)(-0.843) h(-1)], then N budgets were also computed subtracting N lost in the form of cast molts and eggs from the initial stock. Calculations revealed that allocation of the C stock was greatest to egg production ( 34 - 57%), followed by respiration (27%) and cast molts (3%), leaving residual C of 13 - 36% in spent C6 females. The present results for N. cristatus from the North Pacific are compared with those of Calanus spp. in the North Atlantic.
  • A Yamaguchi, Y Watanabe, H Ishida, T Harimoto, K Furusawa, S Suzuki, J Ishizaka, T Ikeda, M Mac Takahashi
    JOURNAL OF OCEANOGRAPHY 60 4 773 - 787 2004年08月 [査読有り][通常論文]
     
    As part of the research program WEST-COSMIC Phase 1 (1997-2001), vertical profiles down to the greater depths (0-2000 in or 5800 in) of the plankton community structure composed of heterotrophic bacteria, phytoplankton, protozooplankton and metazooplankton were studied at one station in each subarctic (44degreesN) and in transitional region (39degreesN), and two stations in subtropical region (30degreesN and 25degreesN); all in 137-155degreesE in the western North Pacific Ocean. The biomass of all four taxonomic groups decreased rapidly with increasing depths at all stations, although the magnitude of depth-related decrease differed among the groups. As plankton community structure, metazooplankton biomass and bacterial biomass occupied >50% of the total in 0-2000 and 2000-4000 or 5000 in strata, respectively, at subarctic and transitional stations, while bacterial biomass contributed to >50% of the total consistently from 0 through 4800 or 5800 in at subtropical stations. Metazooplankton biomass integrated over the greater depths exhibited a clear latitudinal pattern (high north and low south), but this was not the case for those of the other taxonomic groups. As a component of metazooplankton, an appreciable contribution of diapausing copepods to the metazooplankton was noted at subarctic and transitional stations, but they were few or nil at subtropical stations. As protozooplankton assemblages, heterotrophic microflagel fates (HMF) and dinoflagellates were two major components at subarctic and transitional stations, but were only HMF predominated at subtropical stations. From biomass ratios between heterotrophic bacteria, HMF and dinoflagellates, "sinking POC-DOC-heterotrophic bacteria- HMF-heterotrophic dinoflagellates" link was proposed as a microbial food chain operative in the deep layer of the western North Pacific. All results are discussed in the light of latitudinal differences in the structure and functioning of plankton community contributing to the 'biological pump' in the western North Pacific Ocean.
  • H Takata, K Kuma, S Iwade, Y Yamajyoh, A Yamaguchi, S Takagi, K Sakaoka, Y Yamashita, E Tanoue, T Midorikawa, K Kimura, J Nishioka
    MARINE CHEMISTRY 86 3-4 139 - 157 2004年05月 [査読有り][通常論文]
     
    Sources of natural Fe(III)-complexing organic ligands which control vertical distributions of Fe(III) hydroxide solubilities [Fe(III) solubility, < 0.025 mum] and labile dissolved Fe (< 0.22 mum) concentrations were studied at the subarctic and subtropical surface waters (5-300-m depth) in the northwestern North Pacific Ocean during June 2002. High Fe(III) solubility values (0.71.3 nM) were observed at the depth of high chlorophyll a (Chl a) concentrations in the surface mixed layer with no strong correlation between Fe(III) solubility and size-fractionated Chl a concentrations. However, a significant correlation was found between Fe(Ill) solubility values and heterotrophic bacteria abundance at 5 - 100-m depth in the subarctic coastal water. The high Fe(III) solubility observed in the surface mixed layer is probably due to the production of natural Fe(III)-complexing organic ligands, such as siderophores, which were possibly released by specific phytoplankton or bacteria species. Higher Fe(III) solubility values than the labile dissolved Fe concentrations in the surface waters indicate that natural Fe(III)-complexing organic ligands are in excess of labile dissolved Fe concentrations. The Fe(III) solubility levels appeared to increase with depth in mid-depth waters (100-300-m depth), especially in the subarctic waters, in association with higher iron levels (labile dissolved Fe and dissolvable Fe concentrations), nutrient concentrations and humic-type fluorescence intensity. The relatively strong linear correlations between labile dissolved Fe concentrations or Fe(III) solubility values and humic-type fluorescence intensity in mid-depth waters suggest that the labile dissolved Fe concentrations and Fe(III) solubility in mid-depth waters are primarily associated with humic-type fluorescent organic matter produced through the oxidative decomposition and transformation of sinking biogenic organic matter. Humic-type fluorescent organic matter (i.e., marine dissolved humic substances) may thus account for a significant fraction of the Fe(III)-complexing organic ligands, which control Fe(III) solubility and labile dissolved Fe concentrations in mid-depth waters. (C) 2004 Elsevier B.V. All rights reserved.
  • A Yamaguchi, T Ikeda, Y Watanabe, J Ishizaka
    Zoological Studies 43 2 475 - 485 2004年04月 [査読有り][通常論文]
     
    Vertical distribution patterns of pelagic copepods as viewed from the predation pressure hypothesis. Zoological Studies 43(2): 475-485. As habitats of pelagic copepods, epipelagic oceanic environments are characterized by greater food availability but higher risks of predation. Both food supply and predation risk rapidly drop with increasing depth. We studied day/night vertical distribution patterns of copepodid stages of 6 epipelagic (Neocalanus cristatus, N. flemingeri, N. plumchrus, Eucalanus bungii, Metridia pacifica, and M. okhotensis), 2 mesopelagic (Gaetanus simplex and Pleuromamma scutullata), and 6 bathypelagic copepods (Gaidius variabilis, Paraeuchaeta elongata, P. birostrata, P. rubra, M. asymmetrica, and M. curticauda) based on zooplankton samples collected from depths of 0similar to4000 m at stn. Knot (44degreesN, 155degreesE) in the western subarctic Pacific. All epipelagic species exhibited ontogenetic vertical migration (OVM) characterized by descent with progression of copepodid stages, although species-specific variations in the degree of its magnitude were seen. One of the 6 epipelagic species (M. pacifica) showed diel vertical migration (DVM) behavior by its ascent to upper layers at night. Mesopelagic species were characterized by a lack of OVM, although their older copepodid stages undertook DVM. Bathypelagic species underwent OVM in a pattern that was the opposite (ascent with progression of development) of that of epipelagic species. No DVM behavior was recognized for bathypelagic species. From the viewpoint of the predation pressure hypothesis, these differential vertical distribution modes of copepods living in dissimilar bathymetric strata can be interpreted as results of life history traits toward reducing predation mortality of early (bathypelagic copepods) or late copepodid stages (epipelagic copepods). The absence of OVM in mesopelagic copepods is a life history trait that falls somewhere between these 2 extremes (the DVM behavior of their late copepodid stages apparently imparts an advantage for better feeding). This explanation appears to be consistent with the observation that the fecundity of these copepods decrease with increasing depth. http://www.sinica.edu.tw/zool/zoolstud/43.2/475.pdf.
  • G Padmavati, T Ikeda, A Yamaguchi
    MARINE ECOLOGY PROGRESS SERIES 270 181 - 198 2004年 [査読有り][通常論文]
     
    Vertical distribution and population structure of Metridia pacifica and M, okhotensis were investigated at Site H in the Oyashio region (western subarctic Pacific) to evaluate their life cycle modes. Although recruitment of M pacifica continued throughout the year in the top 250 m of the water column, 2 pronounced generations were recognized. The first generation was characterized by rapid development during the spring phytoplankton bloom (generation length: 2-3 mo), and the second by slow development (generation length: 9-10 mo) with overwintering at Stage 5 in deeper-layers (up to 1000-2000 m). In contrast, M okhotensis was consistently found at depth (250-1000 m) throughout the year, except for excursions to the subsurface layer for spawning during the phytoplankton bloom. Developmental sequences of M okhotensis could not be resolved very clearly, largely because of extremely low abundance of Copepodite Stages 2 and 3 (C2-C3). As a tentative life cycle scenario, the C 1 produced during one year was considered to overwinter and develop to C5 through the phytoplankton bloom of the next year. These C5 overwinter and molt to C6 and reproduce during the phytoplankton bloom of the following year. Thus, the generation length of M okhotensis is estimated as 2 yr. For both species, active spawning and subsequent growth are closely associated with phytoplankton bloom. For overwintering stages of both species, a large deposition of lipid in the body and its gradual decrease toward the onset of phytoplankton bloom of the next year was seen. While no comparable life cycle data is presently available for M. okhotensis, the present results of M pacifica are compared with the results from other regions, showing a large between-region variation in the life cycle patterns of this species. Further, the present results are discussed in the context of broad overwintering mechanisms of pelagic copepods living in high-latitude seas.
  • 山口 篤, 池田 勉
    日本プランクトン学会報 50 2 114 - 119 日本プランクトン学会 2003年08月 [査読有り][通常論文]
  • 山口 篤, 三輪 喜之, 井上 勝夫, 松本 稔範, 志賀 直信
    沿岸海洋研究 41 1 23 - 31 日本海洋学会 2003年08月 [査読有り][通常論文]
     
    北海道南東岸における沿岸親潮の動物プランクトン群集の特徴を明らかにするために,季節的,鉛直的および水平的なネット採集試料の解析を行った.沿岸親潮の流入は2月〜4月に見られ,これは当海域のバイオマスピーク(6月)の前であった.沿岸親潮と親潮接岸分枝ともに最優占分類群はかいあし類で,沿岸親潮中では小型冷水性かいあし類のPseudocalanus newmaniやAcartia longiremisが優占していた.水平的に動物プランクトン個体数とバイオマスはともに水温と正の相関があり,低水温の沿岸親潮中では低かった.これはバイオマスを左右する大型かいあし類の発育段階組成が沿岸親潮では休眠中の後期発育段階のみであったためであった.沿岸親潮の動物プランクトン群集のバイオマスが親潮接岸分枝よりも低い要因として,小型かいあし類が優占することや低温な環境下で成長が遅いこと,および珪藻類ブルームによるかいあし類の再生産効率の低下が影響していると考えられる.
  • Yamaguchi Atsushi, Dalpadado Padmini, Ikeda Tsutomu
    Bulletin of the Fisheries Science of Hokkaido University 54 3 59 - 65 北海道大学 2003年 [査読無し][通常論文]
  • Y Watanabe, A Yamaguchi, H Ishida, T Ikeda, J Ishizaka
    GREENHOUSE GAS CONTROL TECHNOLOGIES, VOLS I AND II, PROCEEDINGS 1683 - 1685 2003年 [査読有り][通常論文]
     
    We observed the lethal effects of high partial pressure of CO2 (pCO(2)) to the pelagic zooplankton. The experiments were performed from the sub-arctic to the sub-tropical region and compared the sensitivities to the high pCO(2) between surface organisms (0 - 500 m) and deep-sea organisms (500 - 1,500 m). When organisms were exposed at a pCO(2) from 500 to 100,000 muatm, half the organisms died within 1 day to 2 weeks after exposure. From the half lethal time (LT50) calculated from the survival curve, higher pCO(2) resulted in earlier death of the zooplankton. However, deep-sea animals in the sub-arctic region were less sensitive to the increasing of pCO(2) compared with the others. The apparent LT50 on higher pCO(2) showed that deep-sea organisms are more tolerant than surface ones.
  • A Yamaguchi, Y Watanabe, H Ishida, T Harimoto, K Furusawa, S Suzuki, J Ishizaka, T Ikeda, MT Masayuki
    DEEP-SEA RESEARCH PART I-OCEANOGRAPHIC RESEARCH PAPERS 49 6 1007 - 1025 2002年06月 [査読有り][通常論文]
     
    As part of the research program Western Pacific Environment Study on CO2 Ocean Sequestration for Mitigation of Climate Change (WEST-COSMIC), vertical distribution and community structure of copepods were studied at Station Knot (44degreesN, 155degreesE) down to 4000 m depth in the western subarctic Pacific. Vertical carbon flux mediated by copepod communities was also estimated. Both abundance and biomass of copepods were greatest in the near surface layer and decreased with increasing depth. Decrease of abundance with depth was best fitted to a power regression model, while that of biomass was best described by an exponential regression model. Copepod carcasses occurred throughout the layer, and carcasses/living specimens ratios were greatest in the deepest layer (the ratio was 9.3 at 3000-4000 m depth). A total of 98 calanoid copepod species belonging to 38 genera and 15 families occurred in the 0-4000 m water column (Cyclopoida, Harpacticoida and Poecilostomatoida were not identified to species). The number of genera and species showed bimodal vertical distributions with peaks at 500-1000 m and at 2000-3000 m both during day and night. Based on the species similarity indices, copepod community could be classified into epipelagic, mesopelagic and bathypelagic communities. Based on the feeding pattern, copepods were divided into four types: suspension feeders, suspension feeders in diapause, detritivores and carnivores. In terms of abundance, the most dominant group was suspension feeders (mainly the cyclopoid genus Oithona) in the epipelagic zone, and detritivores (mainly Poecilostomatoida genus Oncaea) were dominant in the meso- and bathypelagic zones. In terms of biomass, suspension feeders in diapause (calanoid genera Neocalanus and Eucalanus) were the major component (ca. 70%), especially at 200-2000 m depth. Comparison of vertical flux of particulate carbon with estimated copepod ingestion/egestion rates suggests that the suspension feeding copepods receive sufficient food. For detritivorous copepods, copepod carcasses, a possible food source, are not abundant enough, so other food sources need to be considered. As a food source for carnivorous copepods, the abundance of suspension feeding and detritivorous copepods appears to be high enough to meet their demand. Our calculation showed that an average of 32% of the particulate carbon flux is consumed by copepods in the 0-4000 m water column. (C) 2002 Elsevier Science Ltd. All rights reserved.
  • A Yamaguchi, Y Watanabe, H Ishida, T Harimoto, K Furusawa, S Suzuki, J Ishizaka, T Ikeda, MM Takahashi
    DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY 49 24-25 5513 - 5529 2002年 [査読有り][通常論文]
     
    As part of the research program "WEST-COSMIC (Western Pacific Environment Study on CO2 Ocean Sequestration for Mitigation of Climate Change)", vertical distribution patterns of community structure and size spectra of plankton organisms were studied at three sites: Station SA at 44degreesN, 155degreesE (down to 4000 m depth); Station I at 39degreesN, 147degreesE (2000 m depth); and Station ST at 25degreesN, 147degreesE (4800 m depth) in the western North Pacific Ocean. The plankton organisms were divided into four major groups (bacteria, phytoplankton, protozooplankton, and mesozooplankton) and their sizes and biomass were quantified. Total plankton biomass in the water column ranged from 8180 (night) to 8630 (day) mg cm(-2) at Station ST to 29,800 (day) to 32,800 (night) mg C m(-2) at Station SA. The water column-integrated major group compositions (biomass) were different between stations: mesozooplankton were the most dominant group (47-52%) at the two northern stations, while they constituted 9-14% at the southern station. An appreciable contribution of dormant copepods to higher mesozooplankton. biomass was noted at the northern station, but there were few copepods at the intermediate station and nil at the southern station. The water column-integrated size distribution patterns of plankton communities were characterized by three marked peaks [pico-, micro-(20 mum), and meso- (2000 mum) size] at Station SA, the same three peaks, but with less marked in the micro- and mesosizes at Station 1, and only one peak (pico-size) at Station ST. Biomass each plankton group decreased with increasing depth, and their declining patterns below 100 m depth were well described by a negative power function, with different slopes between groups and also between stations. Within stations, the slope was the greatest for mesozooplankton, followed by phytoplankton and bacteria or protozooplankton. From correlation analyses between the biomass of the four major groups of plankton organisms, a close relation was observed between bacteria and protozooplankton. This bacteria-protozooplankton link, combined with the results of the depth-related changes in the abundance of each major group and size spectrum, is discussed in the light of regional and bathymetric differences in the structure and functioning of plankton community contributing to the 'biological pump' in the western North Pacific Ocean. (C) 2002 Elsevier Science Ltd. All rights reserved.
  • Bulletin of Fisheries Sciences, Hokkaido University 53 11 - 21 2002年 [査読無し][通常論文]
  • Yamaguchi Atsushi, Ikeda Tsutomu
    Bulletin of Fisheries Sciences, Hokkaido University 53 1 1 - 10 北海道大学 2002年 [査読無し][通常論文]
  • 渡辺 雄二, 石田 洋, 山口 篤
    海洋 33 11 813 - 818 海洋出版 2001年11月 [査読無し][通常論文]
  • Y Watanabe, H Ishida, A Yamaguchi, J Ishizaka
    NIPPON SUISAN GAKKAISHI 67 4 764 - 765 2001年07月 [査読有り][通常論文]
  • Plankton Biology and Ecology 48 104 - 113 2001年 [査読有り][通常論文]
  • 渡辺 雄二, 石田 洋, 山口 篤, 石坂 丞二
    日本水産学会誌 67 4 764 - 765 公益社団法人日本水産学会 2001年 [査読無し][通常論文]
  • A Yamaguchi, T Ikeda
    MARINE BIOLOGY 137 1 99 - 109 2000年08月 [査読有り][通常論文]
     
    Vertical distribution, life cycle, and developmental characteristics of the mesopelagic copepod Gaidius variabilis Brodsky in the Oyashio region were investigated by combining analyses of field copepodite populations with laboratory-rearing data of egg hatching and naupliar development. Field samplings from five discrete depths between the surface and less than or equal to 2000 m were made approximately every month for 1 year. Most populations of G. variabilis occurred between 600 and 1000 m depth. A modest degree of reversed diel vertical migration behavior and some stage-specific depth-distribution patterns were noted. All copepodite stages were observed throughout the year, suggesting a year-round spawning of G. variabilis. From a prominent abundance peak of Copepodite Stage 1 (C1) seen in June to August, together with development times of eggs and nauplii obtained in laboratory-rearing experiments, the major spawning season was extrapolated to be April to June, the phytoplankton bloom season. Tracing the peak abundance of each copepodite stage (distinguishing males and females for C4 to C6), the generation times of males and females were deduced as 2 and 1 year, respectively. All between-stage increments in terms of wet-, dry-, and ash-free dry weights were greatest in C3/C4, and least in C5/C6 for both males and females. The increments in C3/C4 and C4/C5 were greater for males than for females, reflecting a longer stage duration of the males. These weights did not increase in C5/C6 males, possibly because feeding ceased in C6 males. These results for G. variabilis are compared with those for some mesopelagic copepods previously reported from other regions.
  • 山口 篤, 石坂 丞二, 渡辺 雄二
    日本プランクトン学会報 47 2 144 - 156 日本プランクトン学会 2000年08月 [査読有り][通常論文]
     
    During the research of "WEST-COSMIC (Western Pacific Environment Assessment Study on C02 Ocean Sequestration for Mitigation of Climate Change)", vertical distribution of plankton community structure was studied at 39°N, 147°E (down to 2000 m) and 44°N, 155°E (down to 4000 m) in the western North Pacific Ocean. Plankton community was largely divided into four major groups (bacteria, phytoplankton, protozooplankton, and metazooplankton) and their biomass were expressed carbon unit by measuring volume and using volume-carbon equations. Total plankton biomass in the water column was 13,873 mgC m^-2 at 39°N, 147°E and 29,772 (daytime) to 32,780 (nighttime) mgC m^-2 at 44°N, 155°E. The water column was divided into three strata: epipelagic (0-200 m); mesopelagic (200-1000 m); bathypelagic (>1000 m), and their contribution to total water-column plankton biomass was 33-38% (epipelagic), 33-37% (mesopelagic), and 25-34% (bathypelagic), respectively. In the epipelagic, the contribution of four major taxa in plankton biomass was nearly equal (ratios of four taxa; bacteria, phytoplankton, protozooplankton, and metazooplankton to the total biomass were 18-25%, 29-38%, 6-25%, and 17-40%, respectively). Below the epipelagic zone, phytoplankton biomass was decreased rapidly (1-2% of total biomass). In the mesopelagic zone, metazooplankton was the most dominated (60-85%) and bacteria was the second (12-28%). These two taxa dominated also in the bathypelagic zone，but the contribution of metazooplankton was decreased (43-47%) while that of bacteria was increased (41-47%). Constantly，the biomass of each taxon (mgC m^-3) was decreased with depth, and the relationship between carbon biomass and depth was expressed by regression model: log10Y = log10a＋b×log10X (or Y=a×X^b), where Y is the biomass (mgC m^-3), X is the depth (m), and a and b are fitting constants. Most of the taxa fitted to the regression well, and the slope (b) of regression was different between taxa: -0.56 for bacteria, -1.32 to -1.34 for phytoplankton, -0.95 for protozooplankton and -0.96 for metazooplankton. Analyzing the relationship between plankton biomass and depth from previous literatures, the appropriate slope (b) value of the regression for each taxon in the western North Pacific was considered as: -0.45 for bacteria, -1.33 for phytoplankton, -0.95 for protozooplankton, and -1.24 for metazooplankton.
  • A Yamaguchi, T Ikeda
    JOURNAL OF PLANKTON RESEARCH 22 1 29 - 46 2000年01月 [査読有り][通常論文]
     
    Diel and seasonal vertical distribution, life cycle and body allometry of Pleuromamma scutullata and Heterorhabdus tanneri were investigated in the Oyashio region during September 1996 through October 1997. Monthly samples were collected with 0.1 mm mesh closing nets towed through five discrete depths between the surface and less than or equal to 2000 m. Copepodite stages 1 through 6 of P. scutullata and 3 through 6 of H. tanneri were collected effectively with the nets. Day-night samplings during December 1996, April and October 1997 revealed both species ascend at night. Seasonal differences in the vertical distribution patterns of both copepods were insignificant, and P. scutullata was distributed at a much shallower depth (250-500 m) than H. tanneri (600-850 m). By tracing the sequential changes in abundance peaks of each copepodite stage, both species are considered to produce one generation per year. The main reproduction season was estimated to occur in spring for P. scutullata and in winter for H. tanneri. The relationships between prosome length and wet weight, dry weight, and ash-free dry weight indicated that the increase in weight per molt was much greater in H. tanneri than in P. scutullata. These dissimilar features are discussed in relation to the dissimilar food habits of these two species and the production cycle of food organisms in the Oyashio region.
  • Yamaguchi A, Ikeda T, Hirakawa K
    Plankton Biology and Ecology 46 1 54 - 61 Plankton Society of Japan 1999年 [査読有り][通常論文]
     
    The seasonal population structure (copepodite-2 stage through adults) and diel vertical migration pattern of Scolecithricella minor in Toyama Bay, southern Japan Sea, were investigated.Eggs and nauplii were reared in the laboratory at three different temperatures (0.5, 5 and 10°C) as abasis to estimate generation length. Most copepodite stages occurred throughout the year; youngcopepodites (C2 to C5) were most abundant in May-October, while adults were most abundant inMarch-August. Reproduction continued throughout the year, with a peak in April-August. All copepodite stages were consistently distributed at 100-400 m depth. Limited nocturnal ascent was seen inadults, but not always for younger copepodites. Based on habitat temperature, development times of eggs and nauplii expressed as a function of temperature, and assumed proportion of these developmental times in one life cycle of calanoid copepods, the generation length of S. minor was estimated to be 44-76d. Using this estimated generation length range as a guide, the sequential development of five cohorts was identified. An additional two extra cohorts, which were not clearly traceable, are considered to have occurred for a total of 7 cohorts per year for S. minor in Toyama Bay. The present data on the vertical distribution of S. minor are compared with those reported from other regions for the same species. Since S. minor is considered to be a typical detritus feeder, trophic-type-related sequences in major reproduction seasons are discussed by comparing the data of other calanoid copepods reported from Toyama Bay.
  • Yamaguchi A, Ikada T, Shiga N
    Plankton Biology and Ecology 45 183 - 193 1998年 [査読有り][通常論文]
  • 山口 篤, 志賀 直信
    日本プランクトン学会報 44 1 11 - 20 日本プランクトン学会 1997年08月 [査読有り][通常論文]

MISC

書籍等出版物

  • 日本古生物学会 (担当:分担執筆範囲:プランクトン, プランクトンの生態と生存戦略, 生物生産, プランクトンネット)
    丸善出版 2023年01月 (ISBN: 9784621307588) xxiv, 754p, 図版 [8] p
  • 水産科学・海洋環境科学実習
    山口 篤, 今井一郎, 平譯 享, 松野孝平 (担当:分担執筆範囲:プランクトン・微生物関係)
    海文堂 2019年08月
  • New Frontiers in Crustacean Biology (Crustaceana Monographs, 15)
    Brill Academic Publishers 2011年
  • Ecosystem processes during the Oyashio spring bloom
    Elsevier 2010年
  • Marine Ecosystems of the North Pacific Ocean, 2003-2008
    North Pacific Marine Science Organization 2010年
  • Pacific and Arctic Oceans: New Oceanographic Research
    Nova Science Publishers 2008年

所属学協会

  • 日本水産学会   日本プランクトン学会   日本海洋学会   日仏海洋学会   水産海洋学会   Fisheries Oceanography Society of Japan   Oceanographic Society of Japan-France   Plankton Society of Japan   Oceanographic Society of Japan   

Works（作品等）

共同研究・競争的資金等の研究課題

  • 日本学術振興会：科学研究費助成事業 基盤研究(A)
    研究期間 : 2022年04月 -2027年03月 
    代表者 : 山口 篤, 松野 孝平
  • 日本学術振興会：科学研究費助成事業 挑戦的研究(開拓)
    研究期間 : 2020年07月 -2026年03月 
    代表者 : 山口 篤
     
    今年度はかいあし漁業の内容を広く一般に普及させるための情報発信を主に行った。国内学会の発表２件に加え、Fish of the Month (FoM) という、北海道大学水産学部の研究成果を紹介するHPにおいて、本科研費の研究分担者を主とする５名による、かいあし漁業に関する内容を紹介した。紹介内容と紹介者は以下の通りである：「海洋生態系におけるカイアシ類の重要性とかいあし漁業への夢（山口 篤）」、「カイアシ類の音響探知（向井 徹）」、「カイアシ類の音響散乱特性（福田美亮）」、「カイアシ類を対象とした商業漁業（藤森康澄）」、「カイアシ類-新たな水産脂質供給源として（別府史章）」。 カイアシ類を対象とした研究論文として、北太平洋亜寒帯域に優占する日周鉛直移動を行うカイアシ類Metridia pacificaの一次生産への摂餌インパクトを推定し、呼吸量による輸送量の推定を行った。これは、表層（0-50 m）と深海（50-200 m）の水温条件下において、同種の雌成体を飼育し、呼吸による酸素消費量を測定し、現場の表層における摂餌量の推定と、深海における呼吸による炭素輸送量を推定したものである。夜間の表層における個体数は１平方メートルあたり27～5422個体の間にあり、昼間の表層には本種は出現せず、これは日周鉛直移動の反映と考えられた。日周鉛直移動バイオマスは、１平方メートルあたり1-309 mg Cであった。1日の夜間表層と昼間深海での滞留時間を考慮すると、1日あたり１平方メートルあたりの摂餌量は0.04-11.04 mg Cと推定され、これは現場一次生産量の0-2.4％を占めていた。一方、昼間深海での1日あたり１平方メートルあたりの呼吸量は0.02-9.39 mg Cと計算された。これは有光層からの沈降粒子輸送量の0-10％に相当しており、物質循環における重要性が示された。
  • 日本学術振興会：科学研究費助成事業 基盤研究(B)
    研究期間 : 2019年04月 -2023年03月 
    代表者 : 木元 克典, 山口 篤, 下島 公紀
  • 日本学術振興会：科学研究費助成事業 基盤研究(B)
    研究期間 : 2020年04月 -2023年03月 
    代表者 : 三谷 曜子, 山村 織生, 綿貫 豊, 山口 篤, 中村 知裕
     
    2020年6月に予定していた調査がCOVIDで中止になったため，2021年5月に観光船をチャーターし，調査を実施した．また，2019年度に実施したおしょろ丸調査のデータ解析を進めた．目視調査で最も多く記録された海鳥はハシボソミズナギドリであった（6月29日知床岬沖で65,000羽）．鯨類では，イシイルカ，シャチ，マッコウクジラ，ミンククジラが知床半島の東西で見られたが，ナガスクジラは西側のみで見られた．音響調査により，プランクトンの反応を示す120 kHzの周波数では，能取岬沖と知床半島周辺の東西で大きな反応が見られた一方，魚類の反応を示す38 kHzの周波数では知床半島東側に大きな反応が見られた．CTD-LADCPとXBT観測からオホーツク海沿岸は宗谷暖流水が分布し，根室海峡北部にも海面から水深150dbar付近まで，既に入り込んでいることが明らかになった．また，植物プランクトンの優占分類群では，宗谷暖流が卓越する沿岸域および中冷水では珪藻類，沖合域ではナノ鞭毛藻類と，海域により異なっていた．このような海域差は，水塊間の栄養塩および鉄濃度の違いに起因すると考えられた．動物プランクトンバイオマスには，中型動物プランクトンのカイアシ類Metridia okhotensisが優占し，この種の排泄する糞粒が鉛直的な物質輸送に大きく貢献することが示された．11地点で実施したMOHTネットによる採集では，斜里沖陸棚斜面上部の2地点（B2およびB3）でソコイワシ科に属する魚類マイクロネクトンのまとまった採集がみられた．しかし，両地点は必ずしも鯨類や海鳥類との高密度域とは一致しておらず，これら高次捕食者の分布との関連が薄い可能性が示された．
  • 日本学術振興会：科学研究費助成事業 基盤研究(A)
    研究期間 : 2017年04月 -2022年03月 
    代表者 : 山口 篤, 松野 孝平
     
    今年度は1955年～2013年の59年間にわたり夏季南東部ベーリング海陸棚域にて同一の方法 (NORPAC netの鉛直曳き) により採集されたホルマリン固定動物プランクトン試料に基づき、その湿重量バイオマスの経年変化を明らかにした。バイオマスの経年変動は、海洋環境指標 (PDO、NPI、冬季の海氷範囲、春季の海氷融解期、春季の風応力、南北風、強風の頻度、躍層強度、躍層以浅と躍層以深の水温および塩分、躍層水深) との相関を分散分析により評価した。また海洋環境指標 (PDO、春季の海氷融解期、南北風、躍層強度、躍層以浅と躍層以深の水温および塩分) を用いてStructural Equation Modeling (SEM) 解析も行った。 動物プランクトン湿重量バイオマスはmiddle shelfとouter shelfともに経年的な有意差がみられ、気候レジーム毎に偏差が正と負に交互に変化していた。動物プランクトン湿重量バイオマスに直接的な相関の見られたパラメータは、middle shelfでは、NPI、躍層強度、春季の風応力および海氷融解時期の4パラメータであった。一方outer shelfでは、躍層以浅の水温、冬季の海氷範囲および春季の海氷融解期の3パラメータが有意な関係を持っていた。 これらの結果は現在、論文原稿にまとめつつある。また本研究により導入したZooScanを本格運用し始め、海洋酸性化の影響が大きいとされる浮遊性の有殻翼足類Limacina helicinaの個体群構造を、アリューシャン列島ウニマック水道で採集された試料について解析を行った。ウニマック水道におけるL. helicinaの個体群構造は物理的な内部波などにより集められ、他海域では見られないほど高密度分布を形成することが明らかになった。これらの他の研究成果として論文を７報発表した。
  • 日本学術振興会：科学研究費助成事業 基盤研究(B)
    研究期間 : 2016年04月 -2019年03月 
    代表者 : 相田 真希, 田所 和明, 小針 統, 兵藤 不二夫, 石井 励一郎, 山口 篤
     
    平成29年度まで採集した、①西部北太平洋亜寒帯～亜熱帯・熱帯海域、②ベーリング海峡周辺海域～チャクチ海などで採集した動物プランクトン試料、③北海道～鹿児島までの太平洋側で採集したマイワシ・カタクチイワシ、これらに加え、④ベーリング海西部・東部において動物プランクトン試料を新たに採集し、極域（北極海チャクチ海・南極海）～北西部熱帯海域(北緯14度）における動物プランクトンの炭素・窒素安定同位体比について統計的に解析を行った。 その結果、亜寒帯海域のような高栄養塩環境、また亜熱帯・熱帯海域のような貧栄養塩環境で且つ窒素固定系が卓越するような環境まで、食物網の構造や構成する生物が異なっても、海域に関わらず食物連鎖とN/C同位体比には統一的な規則性があることが確認された。炭素同位体比に関し、生物の同位体比は水温や日射、栄養塩濃度によって大きく変動し、高緯度域ほど炭素同位体比は軽く、低緯度域では軽いという特徴が得られた。窒素安定同位体比では、藻類の窒素同化時の主要基質によって決定されるものの、栄養塩同化時に強い制限（例えば、必須元素である鉄や低温、弱光量など環境に起因するもの）がかかると窒素同位体比が大きく変化する。これは藻類の同化速度（生育速度）に起因するものであるが、動物プランクトンの窒素同位体比においても、その環境要因が反映されていることがライン観測結果から得られた。 沖縄～鹿児島近海までの黒潮流域のメソ動物プランクトン群集の同位体分析から、外洋域ほど再生栄養塩・窒素固定に由来するエネルギー源を利用している可能性が示唆された。また、同海域で採集した群体珪藻・群体シアノバクテリア、稚仔魚群集の同位体比から、局所的に発生する藻類は黒潮生態系の主なエネルギー供給源とはなっておらず、黒潮流域の稚仔魚の餌料源は小型カイアシ類であることが推定された。
  • 日本学術振興会：科学研究費助成事業 国際共同研究加速基金(国際共同研究強化)
    研究期間 : 2016年 -2018年 
    代表者 : 山口 篤
     
    2018年3月19日～2019年3月17日にかけて米国ウッズホール海洋研究所にて滞在研究を行った。滞在時の研究テーマとして、北極海の氷上定点において、1996年10月-1997年9月にかけて10-14日間隔で行われた、海表面から水深3500 mまでを最大8層に分けた30回の鉛直区分採集により採集されたホルマリン固定試料中に出現する、中層性カイアシ類の生活史解析を行った。 肉食性種のParaeuchaeta glacialisは初期発育段階（C1)と雌雄成体（C6F/M）は主に500 m以深の深海に分布するが、中～後期の発育段階では水深100 m以浅に分布する、特徴的な発育に伴う鉛直移動を持つことが明らかになった。各発育段階の鉛直分布は、重量での脱皮間成長と関係があり、浅い層に分布する発育段階ほど脱皮間成長が大きく、深層に分布する発育段階の脱皮間成長は小さかった。同様の現象は親潮域の同属（P. elongata）にも知られており、産卵数の少ないParaeuchaeta属は抱卵成体や初期発育段階の時には捕食を避けるために深海に分布するが、遊泳力のついた中～後期発育段階では、より大きな成長を成し遂げるために、餌の豊富な表層に上昇移動した結果と解釈された。その他には中層性粒子食性種のScaphocalanus magnusの生活史を解析し、雌雄で発育速度が異なり、雌は成体（C6F）の状態で長い時間を過ごすのに対し、雄成体は口器付属肢が退化し、その寿命は短いことが明らかになった。中層性の粒子食性カイアシ類においてC6Fでの滞留時間を長くすることは、餌供給量が増加・好転した際に、速やかに再生産に移れる点で有利な生活史戦略であるといえる。 これら2つの研究内容はいずれも帰国前に英文の論文原稿をまとめ、受け入れ研究者のAshjian博士による校閲を受けた。他に関連する論文7報を発表した。
  • 日本学術振興会：科学研究費助成事業 新学術領域研究(研究領域提案型)
    研究期間 : 2012年06月 -2017年03月 
    代表者 : 神田 穣太, 喜多村 稔, 西川 淳, 青野 辰雄, 山口 篤, 高木 省吾, 土屋 光太郎, 立田 穣, 林 敏史, 野田 明, 渡辺 豊, 茂木 正人, 田中 祐志, 守屋 繁春, 小林 卓也, 芳村 毅, 石丸 隆, 五十嵐 敏, 須賀 次郎, 山川 紘, 大津 秀暁, 伊藤 友加里, 高澤 伸江, 内山 香織, 久保 篤史, 今井 圭理
     
    海洋生態系における福島第一原子力発電所事故由来の放射性物質について、以下の研究を行った。１）福島沿岸域において生物と環境の放射性セシウムについて、年に2回の船舶観測による経時的なデータセットを得た。また外洋域の動物プランクトンについても複数の海域で時系列データを得た。２）岩礁性の底生魚に重点を置いて、生態系への移行経路を検討した結果、懸濁・沈降粒子や堆積物の有機物画分等からの移行は小さいことを確認した。３）現場観測データを用い、生態系内の放射性セシウム推移をモデルにより再現し、海洋生物の放射能レベルの今後の推移について検討した。
  • 日本学術振興会：科学研究費助成事業 基盤研究(A)
    研究期間 : 2012年04月 -2017年03月 
    代表者 : 山口 篤, 藤森 康澄, 今井 一郎
     
    水産学及び海洋学の両視点において重要な動物プランクトン群集サイズ組成に関して、１．日本近海における水平分布、２．北太平洋全域の水平分布、３．北太平洋全域における表層から深海における鉛直分布、４．チャクチ海における経年変動を明らかにした。 動物プランクトン群集内におけるエネルギー転送効率として、大型カイアシ類Neocalanus属の優占する西部北太平洋亜寒帯域はボトムアップ的な生態系であることが明らかになった。鉛直的な物質輸送により、深海でも亜寒帯域と熱帯-亜熱帯域の群集構造が異なることが明らかになった。経年的にはチャクチ海にて近年動物プランクトンバイオマスが増加していることが明らかになった。
  • 日本学術振興会：科学研究費助成事業 基盤研究(S)
    研究期間 : 2010年04月 -2015年03月 
    代表者 : 原田 尚美, 木元 克典, 菊地 隆, 白岩 善博, 田中 裕一郎, 岸 道郎, 渡邉 英嗣, 西野 茂人, 鈴木 石根, 広瀬 侑, 伊東 素代, 山口 篤, 小野寺 丈尚太郎
     
    近年、海氷融解が最も激しく生じている西部北極海において、海氷減少に伴う低次生態系の生産量変化を時系列に把握し、海洋生態系モデルにこれら現場データを組み込み、低次生物の生産変化の再現や魚類資源の応答の予測を目的として研究を実施してきた。特筆すべき成果として、冬季の海氷下において生物由来粒子が多く沈降しており、海洋中の渦と循環を介した陸棚起源水の輸送が重要であることがわかってきた。またモデルによる理想化実験の結果、陸棚からの輸送が海氷減少によって活発化していることがわかった。以上の知見は、海氷に覆われているため生物にとって不毛の地と見なされていた北極海盆域で生息環境が向上していることを意味する。
  • 日本学術振興会：科学研究費助成事業 若手研究(B)
    研究期間 : 2009年 -2011年 
    代表者 : 山口 篤
     
    夏季の北太平洋亜寒帯域における動物プランクトンを介した物質輸送量として、糞粒生産による受動的な輸送量(パッシブフラックス)と、日周鉛直移動と季節的な鉛直移動による能動的な輸送量(アクティブフラックス)を推定した。このうち、日周鉛直移動による能動的輸送量は相対的に小さいが、糞粒生産による受動的輸送量と季節的鉛直移動による能動的輸送量はセジメントトラップによる沈降粒子輸送量のそれぞれ20-32%または39%に相当すると推定され、動物プランクトンによる輸送量は、糞粒による受動的輸送量と季節的鉛直移動による能動的輸送量が重要なことが示された。
  • 日本学術振興会：科学研究費助成事業 基盤研究(S)
    研究期間 : 2004年 -2008年 
    代表者 : 岸 道郎, 桜井 泰憲, 飯田 浩二, 帰山 雅秀, 磯田 豊, 綿貫 豊, 山口 篤, 池田 勉, 青木 一郎, 木村 伸吾, 小松 輝久, 松田 裕之, 杉本 隆成, 杉本 隆成, 松田 裕之
     
    日本周辺の黒潮・親潮・対馬暖流の各生態系を対象として, (1) 気候変化に伴う海洋環境と生産力の歴史的変化が生態系構造と機能, 特に低次栄養段階生物の生産, 種多様性, 卓越種交替にどのような影響を与えてきたか(ボトムアップコントロール), (2) 高次生物と漁業活動が各生態系の構造と機能にどのように影響してきたか(トップダウンコントロール), (3) 物理-低次生産-高次生産-資源利用に関する多様なモデルを作成して20世紀以降の海洋生態系の歴史的変遷を評価し, (4) 将来の気候変化と人間活動に応答する生態系変化を予測するための生態系モデルを構築して, 日本周辺の海洋生態系の多様性保全と生物資源の最適な資源利用方策を策定することを目標とする。
  • 日本学術振興会：科学研究費助成事業 若手研究(B)
    研究期間 : 2003年 -2004年 
    代表者 : 山口 篤
     
    西部北太平洋を中心とする北太平洋全域で採集された動物プランクトン試料について湿重量、乾燥重量、C,H,N量、灰分量、有機物重量およびカロリー量を測定し、各8単位間のバイオメトリー式を求めた。いずれの単位間も両対数式で極めて有意な関係式を得ることができた(p<0.0001)。これまで動物プランクトンバイオマスは作業時間効率の観点より、その多くが1つの単位(湿重量が多い)でしか測定されていなかったが、本研究で得られたバイオメトリー式を用いることによって他の単位で表示することができるようになり、海洋における物質循環にはたす動物プランクトンの役割をより正確かつ定量的に把握することが可能となった。 本研究において得られた動物プランクトン各単位間のバイオメトリー式を他の海域(北大西洋、サルガッソー海)で報告されている関係式と比較したところ、炭素量が他の海域に比べて約1.5倍高いことが分かった。この関係式の海域差は、各海域に固有な動物プランクトン相の反映であると解釈できる。北太平洋亜寒帯域の動物プランクトン相に卓越する(バイオマスの60〜80%)大型かいあし類Neocalanus属は体内に脂質を蓄積する(C含有量は乾燥重量の50%を越える)ことが知られている。この主要動物プランクトンの高い脂質の蓄積が、北太平洋亜寒帯域において動物プランクトン炭素量が高い要因であると考えられる。このように動物プランクトン各単位間の関係式はそれぞれ海域間で固有の関係式を使用する必要があることがわかった。 平成16年度には上記結果を国際雑誌に投稿し、受理・印刷まで行うことができた。また得られたバイオメトリー式から代謝量の推定を行う予備実験として、北海道大学練習船おしょろ丸の第154次航海に乗船し、動物プランクトン呼吸量の船上飼育実験を行い、良好な結果を得た。
  • 日本学術振興会：科学研究費助成事業 基盤研究(A)
    研究期間 : 2002年 -2004年 
    代表者 : 池田 勉, 志賀 直信, 山口 篤
     
    本研究は、親潮域を中心とした西部北大平洋域で、水深500-1000mの「中層」、1000-3000mの「深層」に生息する主要な深海性動物プランクトン各種の生活史パラメターと現存量を連続野外採集によって把握するとともに、申請者の考案による簡易型保温コッドエンドを装着した閉鎖式ネットで‘生きている'深海性動物プランクトンを採集し船上実験室で代謝活性の測定と、凍結標本についての体化学成分(電子伝達系(ETS)酵素活性、核酸)の分析を行い、彼らの生理学的・生態学的特性を明らかにする目的で実施した。以下に得られた主要な結果を述べる。 大型植食性カイアシ類で深海に潜って休眠するEucalanus、休眠しないMetridiaの生活史が明らかにされた。中・深層性動物プランクトン群集中、出現個体数で最も優占する体長1mm程度の貝虫類1種とポエキロストマトイダ・カイアシ類数種についてその個体群構造を1年間にわたって解析した結果、世代時間が1-2年と極端に長いことが判明した。彼らの中には、若齢期に上層に分布し、成熟すると下層に移動する個体発生的鉛直移動を行う種も見られた。産卵期は周年にわたるが主産卵期は植物プランクトンの春期ブルーム期とは関係なく、夏-秋であった。クラッチサイズ(抱卵数)は100個を超えることはまれで、表層種より少なく、生涯を通しての捕食圧が中・深層で低いことが伺われた。現存量は、同海域の大型植食性カイアシ類のわずか1-2%程度であった。 代謝活性について、これら貝虫類、ポエキロストマトイダ・カイアシ類を始め、多数の中・深層性カナノイダ・カイアシ類の酸素消費速度は表層性カイアシ類のそれに比べて約1/2程度と低いことが明らかになった。同様の結果はETS活性でも得られた(何れの比較においても水温や体サイズの影響は除去済み)。成長ポテンシャルの指標となる核酸比(RNA/DNA)も表層性種に比べて中・深層カイアシ類で低かった。 これらの結果を総合すると、餌資源の少ない深海環境ではそこに生息している動物プランクトンはゆっくりと遊泳し、成長速度も低く、そのため寿命である可能性が示唆された。

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