研究者情報

マスター

アカウント（マスター）

• 氏名

  伊佐田　智規(イサダ　トモノリ), イサダ　トモノリ

所属（マスター）

• 北方生物圏フィールド科学センター　水圏ステーション　厚岸臨海実験所

所属（マスター）

• 北方生物圏フィールド科学センター　水圏ステーション　厚岸臨海実験所

独自項目

syllabus

• 2021, 生物圏科学特別講義Ⅱ, Special Lecture in Biosphere Science II, 修士課程, 環境科学院, Aquatic Biology, Marine Ecology, Oceanography
• 2021, 大学院共通授業科目（一般科目）：自然科学・応用科学, Inter-Graduate School Classes(General Subject):Natural and Applied Sciences, 修士課程, 大学院共通科目, Marine ecosystem, biodiversity, biological community, hydrodynamics, seagrass beds, kelp forest, statistical data analyses, cold current system
• 2021, 大学院共通授業科目（一般科目）：自然科学・応用科学, Inter-Graduate School Classes(General Subject):Natural and Applied Sciences, 修士課程, 大学院共通科目, Seagrass bed, seaweed bed, kelp forest, biodiversity, plant-animal interactions, eco-physiology, statistical data analyses, cold current system
• 2021, 水圏科学特論Ⅰ, Advanced Course in Aquatic Biology I, 修士課程, 環境科学院, 水圏生物　藻類　海草類　プランクトン　細胞　発生　環境適応　生理生態学　群集生態学　生態系生態学
• 2021, 海洋生態学実習, Field Course in Marine Ecology, 学士課程, 理学部, 厚岸臨海実験所、海洋生態学、プランクトン、ベントス、アマモ場、岩礁潮間帯群集
• 2021, 海洋生態学実習, Field Course in Marine Ecology, 学士課程, 理学部
• 2021, 一般教育演習(ﾌﾚｯｼｭﾏﾝｾﾐﾅｰ), Freshman Seminar, 学士課程, 全学教育, 北海道東部、別寒辺?川、森林、河川、湿原、汽?、海洋、?態系のつながり、フィールドワーク、?物多様性、?態系機能
• 2021, 一般教育演習(ﾌﾚｯｼｭﾏﾝｾﾐﾅｰ), Freshman Seminar, 学士課程, 全学教育, 森林、河川、沿岸生態系、相互作用、構造、物質循環、生物多様性、自然景観
• 2021, 野外巡検, Field Observation, 学士課程, 水産学部, フィールド実習, 野外観察, 生物相, 生態学

researchmap

プロフィール情報

学位

• 博士（環境科学）（北海道大学）

プロフィール情報

• 姓

  伊佐田, イサダ

• 名

  智規, トモノリ

• ID各種

  201301033681981876

対象リソース

http://www.fsc.hokudai.ac.jp/akkeshi/

業績リスト

研究キーワード

• 炭素循環   海洋生態系   光合成   親潮   基礎生産   生物海洋学   植物プランクトン   

研究分野

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

委員歴

• 2022年04月 - 現在   日本海洋学会 Journal of Oceanography   編集委員
• 2020年 - 現在   Frontiers in Marine Science   Review Editor for Marine Biogeochemistry
• 2016年 - 現在   日本海洋学会 海洋生物学研究会   運営委員

受賞

• 2009年 2008北海道大学グローバルCOE「統合フィールド環境科学の教育研究拠点形成」RAプログラム 優秀研究賞
   

  受賞者: 伊佐田智規
• 2009年 平成21年度 岩手県三陸研究論文 岩手県知事賞
   

  受賞者: 伊佐田智規
• 2008年 2008 North Pacific Marine Science Organization (PICES) PICES BIO Committee Best Presentation Award (Oral)
   

  受賞者: 伊佐田智規

論文

• Impact of a Large Shallow Semi‐Enclosed Lagoon on Freshwater Exchange Across an Inlet Channel

  Shinichiro Kida, Kiyoshi Tanaka, Tomonori Isada, Tomohiro Nakamura

  Journal of Geophysical Research: Oceans 129 1 2023年12月27日 [査読有り]
   

  Abstract The impact of a large shallow semi‐enclosed lagoon on freshwater exchange across an inlet channel is investigated using an idealized numerical model. Lagoons are often found between a river mouth and the ocean; we focus on those where the river discharge rate is small and the inlet channel is narrower and deeper than the lagoon. Tides generate freshwater and oceanic‐water plumes across the channel; a stratified freshwater plume forms in the ocean from the late ebb to early flood phase, while a vertically well‐mixed oceanic‐water plume forms in the lagoon from the late flood to early ebb phase. The shallow depth of the lagoon increases the flow speed of the oceanic‐water plume, which results in the formation of a sharp and vertically well‐mixed salinity front within the lagoon. When this front moves toward the ocean during the ebb phase, vertical mixing increases where the bathymetry deepens and freshwater encounters oceanic water below. Without a dredged bottom slope, the impact of mixing would be greatly reduced within the shallow lagoon and channel, as the shallow depth would limit the subsurface intrusion of oceanic water. The narrow channel further causes the flow to converge and accelerate, enhancing both internal shear‐driven and bottom boundary‐layer mixing at the channel and increasing freshwater plume thickness where it enters the ocean. Sensitivity experiments showed that the role of tidal pumping in freshwater exchange across the channel increases when the lagoon area and tidal mixing increase and when the estuarine Richardson number decreases.
• IOCCG Protocol Series (2022). Aquatic Primary Productivity Field Protocols for Satellite Validation and Model Synthesis.

  Balch, W.M, Carranza, M, Cetinić, I, Chaves, J.E, Duhamel, S, Fassbender, A, Fernandez-Carrera, A, Ferrón, S, García-Martín, E, Goes, J, Gomes, H, Gundersen, K, Halsey, K, Hirawake, T, Isada, T, Juranek, L, Kulk, G, Langdon, C, Letelier, R, López-Sandoval, D, Mannino, A, Marra, J.F, Neale, P, Nicholson, D, Silsbe, G, Stanley, R.H, Vandermeulen, R.A

  IOCCG Ocean Optics and Biogeochemistry Protocols for Satellite Ocean Colour Sensor Validation 7 1 - 201 2022年09月 [査読有り]
  
• Spatial variation in diatom abundance and composition in Biwase Bay and Hamanaka Bay (Eastern Hokkaido, Japan), with reference to environmental features

  Hyojin Ahn, Miho Ito, Naoko Kouchi, Kentaro Watanabe, Hiroya Abe, Tomonori Isada, Masahiro Nakaoka

  PeerJ 10 e13705 - e13705 2022年07月27日 [査読有り]
   

  This study aims to examine the spatial variation of diatom abundance and composition along the nearshore areas of Biwase Bay and Hamanaka Bay, eastern Hokkaido. Terrestrial input via Kiritappu Wetland is expected to affect variation and composition differently depending on the position of the two bays. We conducted an oceanographic survey in June 2014 to measure seawater temperature, salinity, colored dissolved organic matter (CDOM) absorption, nutrient concentrations, and total and size-fractionated chlorophyll (Chl) a concentration at 11 stations of the shallowest (<5 m) parts of the bays. These were grouped into four areas (Areas 1 and 2 in Biwase Bay, and Areas 3 and 4 in Hamanaka Bay) based on the distance of the location from the wetland outlet (nearest in Area 1 to the farthest in Area 4). Diatoms are the major primary producers in the water column. Therefore, we also determined genus level cell abundance and diversity of diatoms to compare similarity among areas. Sea surface temperature was the lowest at Area 4, whereas sea surface salinity was the lowest at Area 1. The contribution of CDOM absorption, an indicator of wetland-influenced river discharge, and silica concentration was highest at Area 1. Total amount of nitrite and nitrate concentrations was the highest at Area 4. Total amount of Chl a concentration was also lowest in Area 1. Our size-fractionated Chl a results revealed that while the size composition of phytoplankton varied among areas, micro-sized (>10 µm) phytoplankton were predominant in Area 4. Finally, diatom composition at the genus level differed greatly among areas. Pennate diatoms were predominant in Areas 1 and 2, but centric diatoms dominated in Areas 3 and 4. Our results suggested great spatial variability in oceanographic conditions among areas, with less influence of wetland and more influence of Coastal Oyashio Water based on distance from the wetland outlet. Diatom composition showed geographical division between Biwase and Hamanaka Bays.
• Performance of primary production algorithm using absorption coefficient of phytoplankton in the Pacific Arctic

  Ryosuke Futsuki, Toru Hirawake, Amane Fujiwara, Hisatomo Waga, Takashi Kikuchi, Shigeto Nishino, Tomonori Isada, Koji Suzuki, Yutaka W. Watanabe

  Journal of Oceanography 2022年06月08日 [査読有り]
  
• Morphological variation and phylogeny of Karenia selliformis (Gymnodiniales, Dinophyceae) in an intensive cold-water algal bloom in eastern Hokkaido, Japan

  Mitsunori Iwataki, Wai Mun Lum, Koyo Kuwata, Kazuya Takahashi, Daichi Arima, Takanori Kuribayashi, Yuki Kosaka, Natsuki Hasegawa, Tsuyoshi Watanabe, Tomoyuki Shikata, Tomonori Isada, Tatiana Yu. Orlova, Setsuko Sakamoto

  Harmful Algae 114 102204 - 102204 2022年05月 [査読有り]
   

  Harmful algal blooms responsible for mass mortalities of marine organisms have been rare in Hokkaido, northern Japan, although fish-killing blooms have been frequently reported from western Japanese coasts. In September-November 2021, a huge and prolonged cold-water bloom occurred along the Pacific coast of eastern Hokkaido, and was associated with intensive mortalities of sea urchin, fish, octopus, shellfish, etc. In this study, morphology and phylogeny of the dominant and co-occurring unarmored dinoflagellates of the Kareniaceae in the bloom were examined by using light microscopy, scanning electron microscopy and molecular phylogeny inferred from ITS and LSU rDNA (D1-D3) sequences. Morphological observation and molecular phylogeny showed that the dominant species was Karenia selliformis, with co-occurrences of other kareniacean dinoflagellates, Kr. longicanalis, Kr. mikimotoi, Karlodinium sp., Takayama cf. acrotrocha, Takayama tuberculata and Takayama sp. The typical cell forms of Kr. selliformis in the bloom were discoid, dorsoventrally flattened, and 35.3-43.6 (39.4 +/- 2.1) mu m in length, which was larger than the cell sizes in previous reports. Transparent cells of Kr. selliformis, lacking chloroplasts or having a few shrunken chloroplasts and oil droplets, were also found. Cells of Kr. selliformis showed morphological variation, but the species could be distinguished from other co-occurring Karenia species by the nucleus positioned in the hypocone and chloroplasts numerous (46-105) in number and small (2.9-4.6 mu m) in diameter. Cell density of Kr. selliformis exceeding 100 cells mL(-1) was recorded in the temperature range of 9.8-17.6 degrees C. The rDNA sequences determined from Kr. selliformis in the blooms of Hokkaido, Japan in 2021 were identical to those from the bloom in Kamchatka, Russia in 2020.
• Evaluation of retrieving chlorophyll a concentration and colored dissolved organic matter absorption from satellite ocean color remote sensing in the coastal waters of Hokkaido, Japan

  Tomonori Isada, Stanford B. Hooker, Yukiko Taniuchi, Koji Suzuki

  Journal of Oceanography 2022年02月23日 [査読有り][通常論文]
  
• Performance of JAXA’s SGLI standard ocean color products for oceanic to coastal waters: chlorophyll a concentration and light absorption coefficients of colored dissolved organic matter

  Atsushi Matsuoka, Janet W. Campbell, Stanford B. Hooker, François Steinmetz, Kazunori Ogata, Takafumi Hirata, Hiroto Higa, Victor S. Kuwahara, Tomonori Isada, Koji Suzuki, Toru Hirawake, Joji Ishizaka, Hiroshi Murakami

  Journal of Oceanography 78 4 187 - 208 2021年10月23日 [査読有り][通常論文]
   

  We present the performance of JAXA's SGLI standard algorithms for estimating chlorophyll a (chl a) concentration and the light absorption coefficients of colored dissolved organic matter (CDOM) using recently compiled high-quality data obtained from oceanic to coastal waters. Prior to the evaluation of the algorithms, we first compare two forward models (Gordon et al. in J Geophys Res 93(D9):10909-10924, 1988: G88 and Park and Ruddick in Appl Opt 44(7):1236-1249, 2005: PR05) using a wide range of inherent optical properties (IOPs) to (1) examine if the water reflectance is appropriately reproduced and (2) correct measured reflectance in terms of its bidirectionality. Based on a good reproducibility of water reflectance using the PR05, the optimized IOPs are further used for explaining errors in estimates of chl a concentration and CDOM absorption when using the SGLI, the GSM (Maritorena et al. in Appl Opt 41:2705-2714, 2002), and the QAA (Lee et al. in Appl Opt 41:5755, 2002) inversion algorithms. Results show that the mean error for estimating chl a concentration using the SGLI algorithm is 110% for our dataset. Although this error is lower than that of the GSM and the QAA algorithms, a significant underestimate at chl a higher than 2.0 mg m(-3) is observed, which is further shown by independent match-up analyses. Another SGLI CDOM product includes the mean error of 50% and shows deviation at high CDOM range (> 1.0 m(-1)). A similar trend is observed for the GSM but not for the QAA when a global relationship of CDOM to colored detrital matter is applied. The sources of errors are discussed for potentially improving the retrievals.
• Dynamics of Nutrients and Colored Dissolved Organic Matter Absorption in a Wetland-Influenced Subarctic Coastal Region of Northeastern Japan: Contributions From Mariculture and Eelgrass Meadows

  Tomonori Isada, Hiroya Abe, Hiromi Kasai, Masahiro Nakaoka

  Frontiers in Marine Science 8 2021年10月11日 [査読有り]
   

  Coastal oceans interacting with terrestrial ecosystems play an important role in biogeochemical cycles. It is therefore essential to research land–ocean interactions for further understanding of the processes influencing nutrients dynamics in coastal areas. We investigated the seasonal and spatial distribution of nutrient concentrations and light absorption coefficients of colored dissolved organic matter (CDOM), non-algal particles (NAP), and phytoplankton in a wetland-influenced river–eelgrass meadows–coastal waters continuum in the protected and semi-enclosed coastal sea of Akkeshi-ko estuary (AKE) and Akkeshi Bay (AB), Japan from April 2014 to February 2015. The mixing dilution lines of the CDOM absorption coefficient at 355 nm [a_CDOM(355)] relative to salinity predicted by two end-members between freshwater and coastal water showed conservative mixing in AB. Silicate concentrations were significantly correlated with salinity and a_CDOM(355) in AB in each month except for December 2014. These results suggest that silicate and CDOM in AB primarily originates from wetland-influenced river discharge. However, samples collected from the eelgrass meadows of AKE, where mariculture is developed, showed non-conservative mixing of silicate concentrations and a_CDOM(355) with salinity except for June 2014. Elevated phosphate concentrations, probably released from sediments, were also found in the eelgrass meadows of AKE, especially during summer. These results suggest that the metabolic activities of mariculture and seagrass ecosystem significantly contribute to the nutrient cycles and CDOM absorption in AKE and to the distinct water-mass systems inside and outside AKE. The relative absorption properties of NAP [a_NAP(443)], phytoplankton [a_ph(443)], and a_CDOM(443) showed that CDOM is the main factor affecting the light distribution in AKE. However, the relative absorption properties varied seasonally in AB because of spring and autumn phytoplankton blooms and ice cover during winter. Significant relationships were observed between the Secchi disk depth (Z_SD), a_NAP(443), and a_CDOM(443). Chl a concentration and a_ph(443) were not good indicators for predicting Z_SD in our study region. These results suggest that incorporating inherent optical properties and CDOM from mariculture and seagrass ecosystem into ecosystem models could improve predictions of light distribution along the freshwater–eelgrass–coastal waters continuum in optically complex coastal waters.
• Correction: Kulk et al. Primary production, an index of climate change in the ocean: Satellite-based estimates over two decades (Remote Sens., (2020), 12, (826), 10.3390/rs12050826)

  Gemma Kulk, Trevor Platt, James Dingle, Thomas Jackson, Bror F. Jönsson, Heather A. Bouman, Marcel Babin, Robert J. W. Brewin, Martina Doblin, Marta Estrada, Francisco G. Figueiras, Ken Furuya, Natalia González-Benítez, Hafsteinn G. Gudfinnsson, Kristinn Gudmundsson, Bangqin Huang, Tomonori Isada, Žarko Kovač, Vivian A. Lutz, Emilio Marañón, Mini Raman, Katherine Richardson, Patrick D. Rozema, Willem H. van de Poll, Valeria Segura, Gavin H. Tilstone, Julia Uitz, Virginie van Dongen-Vogels, Takashi Yoshikawa, Shubha Sathyendranath

  Remote Sensing 13 17 2021年09月01日 

  Since the article “Primary Production, an Index of Climate Change in the Ocean: Satellite-Based Estimates over Two Decades” by Kulk et al. [1] was published, we discovered an error in the code of the primary production model, which crept in when the code was updated from the original version described by Platt and Sathyendranath (1988), Sathyendranath et al. (1995) and Longhurst et al. (1995) ([2,31,52] in [1]). The main error in the code led to a time interval for the integration of daily water-column primary production that was shorter than it should have been. As a consequence, daily surface irradiance and hence primary production were systematically underestimated by 20–25% for the entire time series. We also discovered that the Photosynthetic Active Radiation (PAR) products of the National Aeronautics and Space Administration (NASA) that were used to scale the daily light cycle were rounded down for 2003–2019 (MODIS years), which led to an additional but small underestimation of daily surface irradiance. In addition to addressing these errors, we have included a merged time series of the PAR product to remove inter-sensor biases (as described in the corrected text of Appendix B see below). The main corrections increased our estimate of global annual primary production on average by +23.9% between 1998 and 2018, while the correction of the rounding error in the PAR products increased global annual primary production between 2003 and 2018 by +0.9%. Inclusion of the merged PAR product in the primary production model caused a −0.25% decrease in global annual primary production between 1998 and 2002 and a +0.08% increase between 2003 and 2010 (relative to the aforementioned +23.9% increase for the entire time series). Our estimate of global annual primary production between 1998 and 2018 now is 48.7 to 52.5 Gt C y−1 instead of the published estimate of 38.8 to 42.1 Gt C y−1 . Although this is a substantial increase in the estimate of primary production, the results of the sensitivity analysis in which the photosynthesis versus irradiance parameters were varied by ±1 standard deviation and, importantly, the observed trends in regional and global annual primary production are largely unchanged. We therefore consider the outcomes of the study still valid after the corrections. We also note that our corrected estimate of global annual primary production is still within the range of earlier reports (32.0–70.7 Gt C y−1 [5,104] in [1]).
• Spectral modes of radiometric measurements in optically complex waters

  Stanford B. Hooker, Henry F. Houskeeper, Raphael M. Kudela, Atsushi Matsuoka, Koji Suzuki, Tomonori Isada

  Continental Shelf Research 219 104357 - 104357 2021年04月 [査読有り]
  
• Primary Production, an Index of Climate Change in the Ocean: Satellite-Based Estimates over Two Decades

  Gemma Kulk, Trevor Platt, James Dingle, Thomas Jackson, Bror F. Jönsson, Heather A. Bouman, Marcel Babin, Robert J. W. Brewin, Martina Doblin, Marta Estrada, Francisco G. Figueiras, Ken Furuya, Natalia González-Benítez, Hafsteinn G. Gudfinnsson, Kristinn Gudmundsson, Bangqin Huang, Tomonori Isada, Žarko Kovac, Vivian A. Lutz, Emilio Marañón, Mini Raman, Katherine Richardson, Patrick D. Rozema, Willem H. van de Poll, Valeria Segura, Gavin H. Tilstone, Julia Uitz, Virginie van Dongen-Vogels, Takashi Yoshikawa, Shubha Sathyendranath

  remote sensing 12 5 826 - 826 2020年03月 [査読有り][通常論文]
   

  Primary production by marine phytoplankton is one of the largest fluxes of carbon on our planet. In the past few decades, considerable progress has been made in estimating global primary production at high spatial and temporal scales by combining in situ measurements of primary production with remote-sensing observations of phytoplankton biomass. One of the major challenges in this approach lies in the assignment of the appropriate model parameters that define the photosynthetic response of phytoplankton to the light field. In the present study, a global database of in situ measurements of photosynthesis versus irradiance (P-I) parameters and a 20-year record of climate quality satellite observations were used to assess global primary production and its variability with seasons and locations as well as between years. In addition, the sensitivity of the computed primary production to potential changes in the photosynthetic response of phytoplankton cells under changing environmental conditions was investigated. Global annual primary production varied from 38.8 to 42.1 Gt C yr − 1 over the period of 1998–2018. Inter-annual changes in global primary production did not follow a linear trend, and regional differences in the magnitude and direction of change in primary production were observed. Trends in primary production followed directly from changes in chlorophyll-a and were related to changes in the physico-chemical conditions of the water column due to inter-annual and multidecadal climate oscillations. Moreover, the sensitivity analysis in which P-I parameters were adjusted by ±1 standard deviation showed the importance of accurately assigning photosynthetic parameters in global and regional calculations of primary production. The assimilation number of the P-I curve showed strong relationships with environmental variables such as temperature and had a practically one-to-one relationship with the magnitude of change in primary production. In the future, such empirical relationships could potentially be used for a more dynamic assignment of photosynthetic rates in the estimation of global primary production. Relationships between the initial slope of the P-I curve and environmental variables were more elusive.
• Community composition and photophysiology of phytoplankton assemblages in coastal Oyashio waters of the western North Pacific during early spring (vol 212, pg 81, 2018)

  Kazuhiro Yoshida, Hisashi Endo, Evelyn Lawrenz, Tomonori Isada, Stanford B. Hooker, Ondrej Prasil, Koji Suzuki

  ESTUARINE COASTAL AND SHELF SCIENCE 228 2019年11月 [査読有り]
  
• Corrigendum − Yoshida et al., 2018 (Estuarine, Coastal and Shelf Science (2018) 212 (80–94), (S0272771417310107), (10.1016/j.ecss.2018.06.018))

  Yoshida, K., Endo, H., Lawrenz, E., Isada, T., Hooker, S.B., Pr{\'a}?il, O., Suzuki, K.

  Estuarine, Coastal and Shelf Science 228 2019年
• Responses of phytoplankton assemblages to iron availability and mixing water masses during the spring bloom in the Oyashio region, NW Pacific

  T. Isada, A Hattori-Saito, H. Saito, Y. Kondo, J. Nishioka, K. Kuma, H. Hattori, R. M, L. McKay, K. Suzuki

  Limnology and Oceanography 64 1 197 - 216 2019年 [査読有り][通常論文]
  
• GCOM-C/SGLI OCEAN STANDARD PRODUCTS AND EARLY VALIDATION RESULTS

  Mitsuhiro Toratani, Kazunori Ogata, Koji Suzuki, Joji Ishizaka, Toru Hirawake, Takafumi Hirata, Tomonori Isada, Hiroto Higa, Victor S. Kuwahara, Stanford B. Hooker, Yoko Kiyomoto, Hiroshi Murakami, Yukio Kurihara, Masahiro Hori, Hisatomo Waga, Youhei Yamashita, Akihiko Tanaka

  2019 IEEE INTERNATIONAL GEOSCIENCE AND REMOTE SENSING SYMPOSIUM (IGARSS 2019) 4741 - 4744 2019年 

  GCOM-C/SGLI is a multi-wavelength optical radiometer launched on December 23, 2017. The data provision has started from December 20, 2018. In this research, we briefly introduce standard Level 2 products and their validation results based on in situ data. Mean absolute percentage differences are 16.3 - 69.6% for NLW between 380 - 670 nm, 39 and 64.5% for AOT at 670 nm and 865 nm, 27.9% for CHL and 44.2% for aCDOM. Although the number of in situ validation data are still scare for a few ocean color products, the accuracy of GCOM-C/SGLI data will be improved by our future efforts of calibration/validation activities.
• Community composition and photophysiology of phytoplankton assemblages in coastal Oyashio waters of the western North Pacific during early spring

  K. Yoshida, H Endo, E. Lawrenz, T. Isada, S. B. Hooker, O. Prášil, K. Suzuki

  Estuarine, Coastal and Shelf Science 212 80 - 84 2018年 [査読有り][通常論文]
   

  Globally, the western subarctic Pacific is known as the region with the largest seasonal drawdown in the partial pressure of CO2 due to biological activity, i.e., high spring primary production and particulate organic carbon flux. These distinctive features are mainly caused by intense spring diatom blooms in coastal Oyashio (COY) and Oyashio (OY) waters. Although phytoplankton assemblages in OY waters are rather well studied, little is known about COY waters. In this study, photophysiological properties and phytoplankton community composition in COY waters were investigated during the pre-bloom and bloom periods from March to April 2015. Next-generation sequencing targeting the 18S rRNA gene revealed that the diatom Thalassiosira generally dominated the phytoplankton community and showed distinct differences in the diatom communities in shelf and offshore waters of the COY. Additionally, the relative contribution of Thalassiosira to the total diatom assemblages showed a positive correlation with maximum photosynthetic rates (P-max(B)) occurring throughout this study. Chlorophyll a concentration and primary productivity were also positively correlated with sea surface temperature, suggesting that temperature was a critical factor for bloom development. Short-term on-deck incubation experiments were carried out to examine the role of temperature in determining planktonic photosynthetic processes. Our results showed an increase in P-max(B) with rising temperature in assemblages from the shelf COY waters. Similarly, transcription levels of the diatom-specific rbcL gene, which encodes the large subunit of RuBisCO, also increased with rising temperature in the shelf assemblages. In contrast, temperature had little effect on the maximum photochemical quantum efficiency (F-v/F-m) of photosystem II. The results suggested that the transcription activity of the diatom-specific rbcL gene was upregulated by the increase in temperature, and that led to the higher P-max(B) values and the spring diatom bloom in the shelf COY region.
• Influence of hydrography on the spatiotemporal variability of phytoplankton assemblages and primary productivity in Funka Bay and the Tsugaru Strait

  Tomonori Isada, Toru Hirawake, Satoshi Nakada, Tsukuru Kobayashi, Ken'ichi Sasaki, Yoshiyuki Tanaka, Shuichi Watanabe, Koji Suzuki, Sei-Ichi Saitoh

  ESTUARINE COASTAL AND SHELF SCIENCE 188 199 - 211 2017年03月 [査読有り][通常論文]
   

  Phytoplankton community structures and primary productivity were assessed in relation to the oceanographic conditions in the coastal waters of Funka bay and the eastern end of the Tsugaru Strait, adjacent to southwestern Hokkaido, Japan, from April 2010 to January 2012. Phytoplankton community compositions, as estimated from chemotaxonomic analysis based on high-performance liquid chromatography of pigments, showed diatom blooms during spring in both 2010 and 2011. However, spatial heterogeneity of chlorophyll a (Chl a) concentration and primary productivity were found between regions investigated within and outside of Funka Bay during the spring diatom blooms in April 2010. The low Chl a concentrations within Funka Bay in April 2010 were related to the depletion of dissolved inorganic macronutrients, which implies that this difference was related to both the small inflow of the cold Coastal Oyashio Current (COW),into the bay and the development of clockwise circulation caused by discharge of fresh water into the bay. After the spring diatom blooms, the major phytoplankton groups in the study area were Chl b-containing phytoplanktons (chlorophytes and prasinophytes) because of changes in salinity associated with river discharge during the melting season. The results indicate that these phytoplanktons play an important role in the carbon cycle after the spring bloom in Funka Bay and the eastern end of the Tsugaru Strait. The thermohaline fronts created by the COW and the Tsugaru Warm Water in late February produced north south differences in phytoplankton community structures in the eastern end of the Tsugaru Strait. Diatoms with high Chl a concentrations dominated in the northern section of the front. In the southern section, the proportions of chlorophytes and cryptophytes were high. Increases in cyanobacterial abundance and temperature were detected in both regions. Additionally, the contribution of pico-plus nano-sized phytoplanlcton productivity to the total primary productivity at the surface was concomitant with increases in temperature. Our results suggest that small-sized phytoplankton become more important part of the food web during summer, even in the coastal waters. (C) 2017 Elsevier Ltd. All rights reserved.
• 衛星による海洋基礎生産力の推定

  平譯享, 高尾信太郎, 鈴木光次, 西岡純, 渡邉豊, 伊佐田智規

  海の研究 23 3 65 - 77 日本海洋学会 2017年 [査読有り][通常論文]
  
• Hyperspectral optical discrimination of phytoplankton community structure in Funka Bay and its implications for ocean color remote sensing of diatoms

  Tomonori Isada, Toru Hirawake, Tsukuru Kobayashi, Yuichi Nosaka, Masafumi Natsuike, Ichiro Imai, Koji Suzuki, Sei-Ichi Saitoh

  REMOTE SENSING OF ENVIRONMENT 159 134 - 151 2015年03月 [査読有り][通常論文]
   

  Identification of phytoplankton functional groups is key to understanding marine biogeochemical cycles. For more accurate understanding of phytoplankton community structure and its implications for ocean color remote sensing applications, we investigated seasonal changes in phytoplankton pigments with high-performance liquid chromatography (HPLC), hyperspectral absorption coefficients of detritus (a(d)(lambda)), phytoplankton (a(ph)(lambda)), and colored dissolved organic matter (a(CDOM)(lambda)), and hyperspectral a(ph)(X) derived from remote sensing reflectance (a(ph_Rrs-derived)(lambda)) in the coastal waters of Funka Bay from 2010 to 2012. Chlorophyll a (Chl a) concentrations measured by HPLC ranged from 029 to 8.6 mg m(-3). Phytoplankton community compositions, as estimated by chemotaxonomic analysis (CHEMTAX) based on HPLC phytoplanIcton pigments, showed a seasonal succession of diatoms, chlorophyll b-containing phytoplankton (chlorophytes and prasinophytes), and cyanobacteria. Additonally, to identify the dominant type of phytoplankton with an alternative technique to CHEMTAX analysis, we employed a derivative spectroscopy/similarity index (SI) approach for a(ph)(X) as an optical detection technique for discriminating between different types of phytoplankton. In particular for diatom-dominated stations, SI values relative to the second derivative spectra of a(ph)(lambda) of diatom cultures, isolated from our study region, were significantly higher than those for chlorophyll b-containing phytoplankton- and cyanobacteriadominated stations. Furthermore, we found a strong relationship between the SI values calculated from the second derivative spectra and the composition of diatoms as estimated by CHEMTAX. These results suggest that the two different methods validated each other's performance and precision in estimating relative diatom abundance from bulk samples and that it is possible to optically discriminate the dominance of diatoms using derivative spectra of a(ph)(lambda). We extended this combination approach to hyperspectral a(ph_Rrs_derived)(lambda), using a quasi-analytical algorithm within 400-546 nm range. We found a significant correlation between SI values obtained from the second derivative spectra of a(ph_Rrs-derived)(lambda)/a(ph_Rrs-derived)(443) and the composition of diatoms derived by CHEMTAX, but it was not as high as for a(ph)(lambda) measured by filter-pad analysis. These results indicate that using hyperspectral optical data of a(ph)(lambda) and R-rs(lambda) with derivative spectroscopy is potentially a promising approach to identify seasonal variability in the composition of diatoms in coastal waters. Furthermore, a hyperspectral approach in combination with CHEMTAX analysis as a reference for phytoplankton community structure has proven useful in improving our understanding of phytoplankton community structure in the coastal waters of Funka Bay. (C) 2014 Elsevier Inc All rights reserved.
• Bio-optical properties during the summer season in the Sea of Okhotsk

  Shintaro Takao, Takahiro Iida, Tomonori Isada, Sei-Ichi Saitoh, Takafumi Hirata, Koji Suzuki

  PROGRESS IN OCEANOGRAPHY 126 233 - 241 2014年08月 [査読有り][通常論文]
   

  The Sea of Okhotsk is one of the most productive ocean regions in the world. However, the in situ bio-optical properties, which are crucial for satellite ocean-color of the productivity, remain uncertain in this region because little data have been available. We conducted an in situ observation and evaluated the bio-optical properties in terms of chlorophyll a (ChI a) concentration, spectral remote sensing reflectance (R-rs), and the light absorption coefficients of phytoplankton (a(j)), non-algal particles (a(NAP)), and chromophoric dissolved organic matter (a(CDOM)) in the summer of 2006. The data covered a wide range of Chl a levels in surface waters from 0.3 to 8.5 mg m(-3). At 443 nm, a(CDOM) dominated (64% on average) the total non-water absorption (a(t-w)) in this study area. Based on the in situ R-rs data, surface Chl a concentrations that were estimated using the sea-viewing wide field-of-view sensor (SeaWiFS) OC4v6 and the moderate-resolution imaging spectroradiometer (MOD'S) OC3M algorithms were significantly higher than the in situ data by more than 160% and 260%, respectively. In particular, the largest overestimation occurred in the region where a(CDOM) at 443 nm accounted for more than 80% of a(t-w) near the mouth of the Amur River. However, except the CDOM-rich stations, the performance of the OC4v6 and OC3M algorithms became better (i.e., their mean normalized biases were reduced to 50% and 66%, respectively). We conclude that the operational global algorithms were applicable to the summer season in the Sea of Okhotsk except the CDOM-rich region, in which new approaches for ocean-color algorithms (i.e., local algorithms) would be required. (C) 2014 Elsevier Ltd. All rights reserved.
• Light utilization efficiency of phytoplankton in the Western Subarctic Gyre of the North Pacific during summer

  Yuichi Nosaka, Tomonori Isada, Isao Kudo, Hiroaki Saito, Hiroshi Hattori, Atsushi Tsuda, Koji Suzuki

  JOURNAL OF OCEANOGRAPHY 70 1 91 - 103 2014年02月 [査読有り][通常論文]
   

  We investigated the water-column light utilization efficiency (I) of phytoplankton photosynthesis in the Western Subarctic Gyre (WSG) of the North Pacific during summer 2008. The I values (0.64-1.86 g C [g Chl a](-1) [mol photon](-1) m(2)) obtained were observed to increase significantly with decreasing daily photosynthetic available radiation (PAR) and were generally higher than those of previous studies, not only from the subarctic Pacific but also from the world's oceans. To examine the effect of iron availability on I in the WSG, I values were estimated from the data of two in situ iron fertilization experiments: the Subarctic Pacific Iron Experiment for Ecosystem Dynamics Study I (SEEDS-I) and II (SEEDS-II). We found that iron availability did not affect I values. Overall, this study revealed that I values changed remarkably in the WSG during the summer, and that higher values were found at the stations where moderate PAR levels (ca. 10-30 mol photons m(-2) day(-1)) were observed and where autotrophic flagellates predominated in the phytoplankton assemblages.
• Spatial variability in iron nutritional status of large diatoms in the Sea of Okhotsk with special reference to the Amur River discharge

  K. Suzuki, A. Hattori-Saito, Y. Sekiguchi, J. Nishioka, M. Shigemitsu, T. Isada, H. Liu, R. M. L. McKay

  BIOGEOSCIENCES 11 9 2503 - 2517 2014年 [査読有り][通常論文]
   

  The Sea of Okhotsk is known as one of the most biologically productive regions among the world's oceans, and its productivity is supported in part by the discharge of iron (Fe)-rich water from the Amur River. However, little is known about the effect of riverine-derived Fe input on the physiology of the large diatoms which often flourish in surface waters of the productive continental shelf region. We conducted diatom-specific immunochemical ferredoxin (Fd) and flavodoxin (Fld) assays in order to investigate the spatial variability of Fe nutritional status in the microplanktonsized (20-200 mu m; hereafter micro-sized) diatoms. The Fd index, defined as the proportion of Fd to the sum of Fd plus Fld accumulations in the cells, was used to assess their Fe nutritional status. Additionally, active chlorophyll fluorescence measurements using pulse-amplitude-modulated (PAM) fluorometry were carried out to obtain the maximum photochemical quantum efficiency (F-v / F-m) of photosystem II for the total micro-sized phytoplankton assemblages including diatoms. During our observations in the summer of 2006, the micro-sized diatoms were relatively abundant (> 10 mu g C L-1) in the neritic region, and formed a massive bloom in Sakhalin Bay near the mouth of the Amur River. Values of the Fd index and F-v / F-m were high (> 0.9 and > 0.65, respectively) near the river mouth, indicating that Fe was sufficient for growth of the diatoms. However, in oceanic waters of the Sea of Okhotsk, the diatom Fd index declined as cellular Fld accumulation increased. These results suggest that there was a distinct gradient in Fe nutritional status in the micro-sized diatoms from near the Amur River mouth to open waters in the Sea of Okhotsk. A significant correlation between dissolved Fe (D-Fe) concentration and the Fd index was found in waters off Sakhalin Island, indicating that D-Fe was a key factor for the photophysiology of this diatom size class. In the vicinity of the Kuril Islands between the Sea of Okhotsk and the Pacific Ocean, micro-sized diatoms only accumulated Fld (i.e., Fd index = 0), despite strong vertical mixing consistent with elevated surface D-Fe levels (> 0.4 nM). Since higher Fe quotas are generally required for diatoms growing under low-light conditions, the micro-sized diatoms off the Kuril Islands possibly encountered Fe and light co-limitations. The differential expressions of Fd and Fld in micro-sized diatoms helped us to understand how these organisms respond to Fe availability in the Sea of Okhotsk in connection with the Amur River discharge.
• Improvement of an aquaculture site-selection model for Japanese kelp (Saccharina japonica) in southern Hokkaido, Japan: an application for the impacts of climate events

  Yang Liu, Sei-Ichi Saitoh, I. Nyoman Radiarta, Tomonori Isada, Toru Hirawake, Hiroyuki Mizuta, Hajime Yasui

  ICES JOURNAL OF MARINE SCIENCE 70 7 1460 - 1470 2013年11月 [査読有り][通常論文]
   

  Japanese kelp (Saccharina japonica) is one of the most valuable cultured and harvested kelp species in Japan. In this study, we added a physical parameter, sea surface nitrate (SSN) estimated from satellite remote sensing data, to develop a suitable aquaculture site-selection model (SASSM) for hanging cultures of Japanese kelp in southern Hokkaido, Japan. The local algorithm to estimate SSN was developed using satellite measurements of sea surface temperature and chlorophyll-a. We found a high correlation between satellite-and ship-measured data (r(2) = 0.87, RMSE = 1.39). Multi-criteria evaluation was adapted to the SASSM to rank sites on a scale of 1 (least suitable) to 8 (most suitable). Wefound that 64.4% of the areas were suitable (score above 7). Minamikayabe was identified as the most suitable area, and Funka Bay also contained potential aquaculture sites. In addition, we examined the impact of El Nino/La Nina-Southern Oscillation (ENSO) events on Japanese kelp aquaculture and site suitability from 2003-2010. During El Nino events, the number of suitable areas (scores 7 and 8) decreased significantly, indicating that climatic conditions should be considered for future development of marine aquaculture.
• Influence of Amur River discharge on phytoplankton photophysiology in the Sea of Okhotsk during late summer

  Tomonori Isada, Takahiro Iida, Hongbin Liu, Sei-Ichi Saitoh, Jun Nishioka, Takeshi Nakatsuka, Koji Suzuki

  JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 118 4 1995 - 2013 2013年04月 [査読有り][通常論文]
   

  We investigated the photosynthetic parameters of phytoplankton in the Sea of Okhotsk during the late summer of 2006 to characterize their spatiotemporal variability and to test the hypothesis that discharge from the Amur River could influence the algal photophysiology. The highest maximum quantum yield of carbon fixation in photosynthesis (phi cmax; 0.098mol C mol photons-1) was found near the Amur River mouth, where nitrate was depleted. However, none of the photosynthetic parameters, including primary productivity (PP) at the surface, were correlated with temperature, daily photosynthetically available radiation (PAR), or ambient nutrient concentrations. Variations in phi cmax depended on the variations in not only the mean chlorophyll a specific absorption coefficient of phytoplankton (*ph) but also the slope index of the absorption coefficient of phytoplankton (aph slope), an indicator for the ratio of nonphotosynthetic carotenoids to photosynthetic carotenoids. These results indicated that the phytoplankton assemblages acclimated to the ambient light conditions by regulating their cellular pigments. Additionally, *ph and euphotic depth (Zeu) were significantly correlated with salinity, suggesting that photoacclimation of the phytoplankton assemblages observed in this study could be induced by discharge of Amur River. Because spatiotemporal variations in PP were concomitant with phi cmax, *ph, and the chlorophyll a concentration, PP models based on inherent optical property (IOP) were suitable for estimating PP in the Sea of Okhotsk. This study is the first to investigate the factors controlling phytoplankton photophysiology in the Sea of Okhotsk, one of the highest primary production areas in the world.
• Modeling runoff into a Region Of Freshwater Influence for improved ocean prediction: Application to Funka Bay

  S. Nakada, Y. Ishikawa, T. Awaji, T. In, S. Shima, T. Nakayama, T. Isada, S.-I. Saitoh

  Hydrological Research Letters 6 47 - 52 THE JAPAN SOCIETY OF HYDROLOGY AND WATER RESOURCES 2012年 [査読有り][通常論文]
   

  Regions Of Freshwater Influence (ROFI) existing between oceans and estuaries often yield significant fishery resources. To inform fishermen of the real-time ocean state, an operational prediction system focusing on a specific coastal region would normally require accurate and timely runoff data for all rivers. In this paper, hydrometeorological procedures providing the required runoff data on a daily basis were coupled with an Ocean General Circulation Model (OGCM) to evaluate the impacts of runoff processes on ocean simulations within a ROFI. The procedures we adopted employ a distributed tank model based on water mass and heat budgets derived from predicted meteorological datasets. An exponential relationship between runoff rates and watershed areas was used to determine model parameters in order to estimate the runoff from many other small rivers. The coupled model reproduced a surface salinity field in the bay that was in good agreement with observations, and simulated the expected clockwise circulation generated by the high net total discharge associated with snowmelt. Our results underline the fact that implementation of hydrological processes into ocean simulations is essential for a better understanding of water circulation driven by runoff into semi-enclosed bays over interannual timescales.
  
• Synoptic relationships between surface Chlorophyll-a and diagnostic pigments specific to phytoplankton functional types

  T. Hirata, N. J. Hardman-Mountford, R. J. W. Brewin, J. Aiken, R. Barlow, K. Suzuki, T. Isada, E. Howell, T. Hashioka, M. Noguchi-Aita, Y. Yamanaka

  BIOGEOSCIENCES 8 2 311 - 327 2011年 [査読有り][通常論文]
   

  Error-quantified, synoptic-scale relationships between chlorophyll-a (Chl-a) and phytoplankton pigment groups at the sea surface are presented. A total of ten pigment groups were considered to represent three Phytoplankton Size Classes (PSCs, micro-, nano- and picoplankton) and seven Phytoplankton Functional Types (PFTs, i.e. diatoms, dinoflagellates, green algae, prymnesiophytes (haptophytes), pico-eukaryotes, prokaryotes and Prochlorococcus sp.). The observed relationships between Chl-a and PSCs/PFTs were well-defined at the global scale to show that a community shift of phytoplankton at the basin and global scales is reflected by a change in Chl-a of the total community. Thus, Chl-a of the total community can be used as an index of not only phytoplankton biomass but also of their community structure. Within these relationships, we also found nonmonotonic variations with Chl-a for certain pico-sized phytoplankton (pico-eukaryotes, Prokaryotes and Prochlorococcus sp.) and nano-sized phytoplankton (Green algae, prymnesiophytes). The relationships were quantified with a leastsquare fitting approach in order to enable an estimation of the PFTs from Chl-a where PFTs are expressed as a percentage of the total Chl-a. The estimated uncertainty of the relationships depends on both PFT and Chl-a concentration. Maximum uncertainty of 31.8% was found for diatoms at Chla = 0.49 mg m(-3). However, the mean uncertainty of the relationships over all PFTs was 5.9% over the entire Chl-a range observed in situ (0.02< Chl-a < 4.26 mg m(-3)). The relationships were applied to SeaWiFS satellite Chl-a data from 1998 to 2009 to show the global climatological fields of the surface distribution of PFTs. Results show that microplankton are present in the mid and high latitudes, constituting only similar to 10.9% of the entire phytoplankton community in the mean field for 1998-2009, in which diatoms explain similar to 7.5%. Nanoplankton are ubiquitous throughout the global surface oceans, except the subtropical gyres, constituting similar to 45.5%, of which prymnesiophytes (haptophytes) are the major group explaining similar to 31.7% while green algae contribute similar to 13.9%. Picoplankton are dominant in the subtropical gyres, but constitute similar to 43.6% globally, of which prokaryotes are the major group explaining similar to 26.5% (Prochlorococcus sp. explaining 22.8%), while pico-eukaryotes explain similar to 17.2% and are relatively abundant in the South Pacific. These results may be of use to evaluate global marine ecosystem models.
• Primary productivity and its bio-optical modeling in the Oyashio region, NW Pacific during the spring bloom 2007

  Tomonori Isada, Ai Hattori-Saito, Hiroaki Saito, Tsutomu Ikeda, Koji Suzuki

  DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY 57 17-18 1653 - 1664 2010年09月 [査読有り][通常論文]
   

  Despite large diatom blooms occurring in the Oyashio region of the NW Pacific every spring, our knowledge of factors controlling primary productivity in the region during that season remains incomplete. Therefore, we investigated phytoplankton abundance, size structure, and primary productivity from April to June 2007. Significant changes were observed. Chlorophyll a (Chl a) concentrations in surface waters fluctuated between 0.37 and 17 mg m(-3). Micro-sized (> 10 mu m) phytoplankton dominated the phytoplankton community when Chl a was > 1 mg m(-3). Depth-integrated daily primary production within the euphotic layer ranged between 328 and 3231 mg C m(-2) d(-1). Higher values of the water-column light utilization index (Psi) for phytoplankton photosynthesis were observed in May and June. Although no significant relationships were found between surface primary productivity and macronutrient concentrations or photosynthetically available radiation (PAR), surface primary productivity correlated significantly with Chl a concentration during April, indicating that algal productivity depended on phytoplankton biomass. Furthermore, significant linear relationships were found throughout the observations of phytoplankton absorption coefficient to surface primary productivity and of that coefficient to the optimum algal photosynthetic rate normalized by Chl a level (P-opt(B)) in the water column. Modeling P-opt(B) with the empirical equations of Behrenfeld and Falkowski (1997) or Kameda and lshizaka (2005) did not accurately reproduce in situ P-opt(B). These results suggest that the phytoplankton absorption properties could become useful indicators for estimating primary productivity in the Oyashio region during spring. (C) 2010 Elsevier Ltd. All rights reserved.
• Community structure and photosynthetic physiology of phytoplankton in the northwest subarctic Pacific during an in situ iron fertilization experiment (SEEDS-II)

  Koji Suzuki, Hiroaki Saito, Tomonori Isada, Ai Hattori-Saito, Hiroshi Kiyosawa, Jun Nishioka, R. Michael. L. McKay, Akira Kuwata, Atsushi Tsuda

  DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY 56 26 2733 - 2744 2009年12月 [査読有り][通常論文]
   

  Temporal changes in the abundance, community composition, and photosynthetic physiology of phytoplankton in surface waters were investigated during the second in situ iron (Fe) fertilization experiment in the NW subarctic Pacific (SEEDS-II). Surface chlorophyll a concentration was 0.75 mg m(-3) on the day before the first Fe enrichment (i.e. Day 0), increased ca. 3-fold until Day 13 after two Fe additions, and thereafter declined with time. The photochemical quantum efficiency (F-v/F-m) and functional absorption cross-section (sigma(PSII)) of photosystem II for total phytoplankton in surface waters increased and decreased inside the Fe-enriched patch through Day 13, respectively. These results indicate that the photosynthetic physiological condition of the phytoplankton improved after the Fe infusions. However, the maximum F-v/F-m value of 0.43 and the maximum quantum yield of carbon fixation (phi(max)) of 0.041 mol C (mol photon)(-1) during the development phase of the bloom were rather low, compared to their theoretical maximum of ca. 0.65 and 0.10 mol C (mol photon)(-1), respectively. Diatoms, which were mainly composed of oceanic species, did not bloom, and autotrophic nanoflagellates such as cryptophytes and prasinophytes became predominant in the phytoplankton community inside the Fe-enriched patch. In ferredoxin/flavodoxin assays for micro-sized (20-200 mu m in cell length) diatoms, ferredoxin was not detected but flavodoxin expressions consistently occurred with similar levels both inside and outside the Fe-enriched patch, indicating that the large-sized diatoms were stressed by Fe bioavailability inside the Fe-enriched patch even after the Fe enrichments. Our data suggest that the absence of a Fe-induced large-sized diatom bloom could be partly due to their Fe stress throughout SEEDS-II. (C) 2009 Elsevier Ltd. All rights reserved.
• Photosynthetic features and primary productivity of phytoplankton in the Oyashio and Kuroshio–Oyashio transition regions of the northwest Pacific

  T. Isada, A. Kuwata, H. Saito, T. Ono, M. Ishii, H. Yoshilawa-Inoue, K. Suzuki

  Journal of Plankton Research 31 9 1009 - 1025 2009年09月 [査読有り][通常論文]
   

  Diel and seasonal changes in the photosynthetic physiology of phytoplankton and primary productivity were investigated during 2005, together with community composition in the Oyashio (OY) and Kuroshio-Oyashio transition (TR) regions of the northwest Pacific. In both regions, diel changes in the maximum photosynthetic rate (P*(max)) and the light saturation index (E-k) in the photosynthesis-irradiance (P-E) curve were observed, due to diel differences in photo-physiology. In the OY region, the highest values of chlorophyll a concentration, depth-integrated primary production and the maximum quantum yield of carbon fixation in photosynthesis (Phi(c max)) were observed in May when diatom blooms occurred. Furthermore, a higher water-column light utilization efficiency (Psi) of photosynthesis for phytoplankton was found in the OY region in both May and September. In contrast, in the TR and warm-core ring regions, Phi(c max) was nearly constant, while depth-integrated primary production in May was significantly lower than in the OY region. These results show that the spring phytoplankton assemblages in OY waters had a higher light utilization ability during photosynthesis. Such a high photosynthetic property would contribute to the highest seasonal biological drawdown of surface pCO(2) among the world's oceans (Takahashi, T., Sutherland, S. C., Sweeney, C. et al. (2002) Global sea-air CO2 flux based on climatological surface ocean pCO(2), and seasonal biological and temperature effects. Deep-Sea Res. II, 49, 1601-1622).
• Primary productivity and photosynthetic features of phytoplankton in the Sea of Okhotsk during late summer

  Tomonori Isada, Koji Suzuki, Hongbin Liu, Jun Nishioka, Takeshi Nakatsuka

  PICES Scientific Report No.36 36 2009年08月 [査読無し][通常論文]
  
• 夏季のオホーツク海および千島列島海域における基礎生産過程の特徴

  鈴木光次, 伊佐田智規, Hongbin Liu, 飯田高大

  月刊海洋 No.50, 99-106  2008年 [査読無し][通常論文]
  
• Evidence for the grazing hypothesis: Grazing reduces phytoplankton responses of the HNLC ecosystem to iron enrichment in the western subarctic pacific (SEEDS II)

  Atsushi Tsuda, Shigenobu Takeda, Hiroaki Saito, Jun Nishioka, Isao Kudo, Yukihiro Nojiri, Koji Suzuki, Mitsuo Uematsu, Mark L. Wells, Daisuke Tsumune, Takeshi Yoshimura, Tatsuo Aono, Takafumi Aramaki, William P. Cochlan, Maki Hayakawa, Keiri Imai, Tomoshi Isada, Yoko Iwamoto, William K. Johnson, Sohiko Kameyama, Shungo Kato, Hiroshi Kiyosawa, Yoshiko Kondo, Maurice Levasseur, Ryuji J. Machida, Ippei Nagao, Fumiko Nakagawa, Takahiro Nakanish, Seiji Nakatsuka, Akira Narita, Yoshifumi Noiri, Hajime Obata, Hiroshi Ogawa, Kenji Oguma, Tsuneo Ono, Tomofumi Sakuragi, Motoki Sasakawa, Mitsuhide Sato, Akifumi Shimamoto, Hyoe Takata, Charles G. Trick, Yutaka W. Watanabe, Chi Shing Wong, Naoki Yoshie

  JOURNAL OF OCEANOGRAPHY 63 6 983 - 994 2007年12月 [査読有り][通常論文]
   

  mesoscale iron-enrichment study (SEEDS II) was carried out in the western subarctic Pacific in the summer of 2004. The iron patch was traced for 26 days, which included observations of the development and the decline of the bloom by mapping with sulfur hexafluoride. The experiment was conducted at almost the same location and the same season as SEEDS (previous iron-enrichment experiment). However, the results were very different between SEEDS and SEEDS II. A high accumulation of phytoplankton biomass (similar to 18 mg chl m(-3)) was characteristic of SEEDS. In contrast, in SEEDS II, the surface chlorophyll-a accumulation was lower, 0.8 to 2.48 mg m(-3), with no prominent diatom bloom. Photosynthetic competence in terms of F-v/F-m for the total phytoplankton community in the surface waters increased after the iron enrichments and returned to the ambient level by day 20. These results suggest that the photosynthetic physiology of the phytoplankton assemblage was improved by the iron enrichments and returned to an iron-stressed condition during the declining phase of the bloom. Pico-phytoplankton (< 2 mu m) became dominant in the chlorophyll-a size distribution after the bloom. We observed a nitrate drawdown of 3.8 mu M in the patch (day 21), but there was no difference in silicic acid concentration between inside and outside the patch. Mesozooplankton (copepod) biomass was three to five times higher during the bloom-development phase in SEEDS II than in SEEDS. The copepod biomass increased exponentially. The grazing rate estimation indicates that the copepod grazing prevented the formation of an extensive diatom bloom, which was observed in SEEDS, and led to the change to a pico-phytoplankton dominated community towards the end of the experiment.

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  宮川和大, 長尾誠也, 芳村毅, 加藤寛己, 伊佐田智規 日本地球化学会年会要旨集(Web) 67th 2020年
• 植物プランクトン群集組成をトレーサーとした秋の道東沿岸海域の水塊分布

  谷内由貴子, 黒田寛, 伊佐田智規, 芳村毅, 葛西広海 水産海洋学会研究発表大会講演要旨集 2018 2018年
• SGLI/GCOM‐Cのための純基礎生産推定アルゴリズム

  平譯享, 夫津木亮介, 新明克人, 藤原周, 伊佐田智規, 高尾信太郎, 鈴木光次, 渡邉豊, 野坂裕一 日本海洋学会大会講演要旨集 2016 120 2016年03月 [査読無し][通常論文]
  
• 北海道東部沿岸域の厚岸沖における植物プランクトン群集組成と光合成特性の季節変化

  伊佐田智規, 平譯享, 鈴木光次, 西岡純, 葛西広海, 阿部博哉 日本海洋学会大会講演要旨集 2016 275 2016年03月 [査読無し][通常論文]
  
• Akkeshi marine station, field science center for northern biosphere, Hokkaido University(from field research sites (26))

  Nakaoka M, Isada T, Honda K, Kitamura T Japanese Journal of Ecology 64 (1) 87 -91 2014年 [査読無し][通常論文]
  
• 噴火湾における植物プランクトン群集組成と基礎生産力の季節変化

  伊佐田智規, 平譯享, 小林創, 西岡純, 鈴木光次, 齊藤誠一 日本海洋学会大会講演要旨集 2013 157 2013年03月11日 [査読無し][通常論文]
  
• AQUACULTURE SITE SELECTION FOR GAGOME KELP, KJELLMANIELLA CRASSIFOLIA, IN SOUTHERN HOKKAIDO, JAPAN, USING SATELLITE REMOTE SENSING AND GIS-BASED MODELS

  SAITOH Sei‐ichi, SHIBATA Haruka, LIU Yang, NYOMAN RADIARTA I, ISADA Tomonori, HIRAWAKE Toru, MIZUTA Hiroyuki, YASUI Hajime 日本リモートセンシング学会学術講演会論文集 54th 403 2013年 [査読無し][通常論文]
  
• 生物地球化学過程に果たす環オホーツク圏の海洋循環・物質循環の役割 夏季の西部北太平洋亜寒帯循環域における植物プランクトンの光合成による水柱の光利用効率

  野坂裕一, 鈴木光次, 伊佐田智規, 齊藤宏明, 津田敦, 服部寛 月刊海洋 44 (8) 473 -477 2012年08月01日 [査読無し][通常論文]
  
• 基礎生産力と海面温度の関係およびその分布

  新明克仁, 平譯享, 高尾信太郎, 伊佐田智規, 藤原周, 齊藤誠一 日本海洋学会大会講演要旨集 2012 277 2012年03月13日 [査読無し][通常論文]
  
• ハイパースペクトルセンサーを用いた植物プランクトン群集(珪藻類)推定方法の開発

  伊佐田智規, 平譯享, 小林創, 松本慧太郎, 野坂裕一, 鈴木光次, 齊藤誠一 日本海洋学会大会講演要旨集 2012 211 2012年03月13日 [査読無し][通常論文]
  
• 噴火湾およびその周辺海域における植物プランクトン群集による基礎生産力の時空間変化

  伊佐田智規, 平譯享, 葛西広海, 小埜恒夫, 渡邉豊, 鈴木光次, 齊藤誠一 水産海洋学会研究発表大会講演要旨集 2011 28 2011年 [査読無し][通常論文]
  
• 2008年夏季の西部北太平洋亜寒帯域における植物プランクトンによる水柱の光合成光利用効率の特性

  野坂裕一, 伊佐田智規, 鋤柄千穂, 齊藤宏明, 津田敦, 鈴木光次 日本海洋学会大会講演要旨集 2010 147 2010年03月15日 [査読無し][通常論文]
  
• 2007年親潮域春季ブルーム期における植物プランクトン群集の光合成特性

  伊佐田智規, 鈴木光次, 齊藤(服部)愛, 齊藤宏明, 葛西広海, 齊藤誠一, 池田勉 日本海洋学会大会講演要旨集 2010 141 2010年03月15日 [査読無し][通常論文]
  
• 親潮域春季ブルームの空間変動要因

  齊藤宏明, 近藤能子, 西岡純, 高橋一生, 中町美和, 岡崎雄二, 伊佐田智規, 桑田晃, 清水勇吾, 鈴木光次 日本海洋学会大会講演要旨集 2009 183 2009年09月11日 [査読無し][通常論文]
  
• 2007年親潮域春季ブルーム期における衛星リモートセンシングを用いた基礎生産の推定

  伊佐田智規, 鈴木光次, 服部愛, 齊藤宏明, 葛西広海, 齊藤誠一, 池田勉 日本海洋学会大会講演要旨集 2009 200 2009年03月23日 [査読無し][通常論文]
  
• 2007年春季親潮ブルームにおける珪藻種組成の特徴

  服部愛, 鈴木光次, 駒崎奈津子, 服部寛, 伊佐田智規, 齊藤宏明, 池田勉 日本海洋学会大会講演要旨集 2009 171 2009年03月23日 [査読無し][通常論文]
  
• ベーリング海およびチャクチ海における生物光学観測

  藤原周, 平譯享, 鈴木光次, 伊佐田智規, 齊藤誠一 日本海洋学会大会講演要旨集 2008 174 2008年03月14日 [査読無し][通常論文]
  
• 水中分光放射特性を用いたmicroplankton群集優占海域の識別

  藤原周, 平譯享, 齊藤誠一, 本多牧生, 松本和彦, 鈴木光次, 伊佐田智規 みらいシンポジウム予稿集 11th 131 2008年03月 [査読無し][通常論文]
  

所属学協会

• Association for the Sciences of Limnology and Oceanography   日本海洋学会   日本地球惑星科学連合   

共同研究・競争的資金等の研究課題

• 沿岸浅海域からの炭素輸送と基礎生産の定量把握

  日本学術振興会：科学研究費助成事業

  研究期間 : 2024年04月 -2028年03月 

  代表者 : 伊佐田 智規, 片岡 剛文, 芳村 毅
• 亜寒帯沿岸生態系における陸域起源栄養塩利用の評価

  日本学術振興会：科学研究費助成事業

  研究期間 : 2022年06月 -2027年03月 

  代表者 : 黒田 寛, 片岡 剛文, 白藤 徳夫, 中野渡 拓也, 鬼塚 年弘, 谷内 由貴子, 伊佐田 智規, 丹羽 健太郎
• アマモ場におけるブルーカーボン貯留経路としての透明細胞外重合物質粒子および粒状有機炭素の変動要因の解明

  公益財団法人 国際エメックスセンター：令和6年度若手研究者活動支援制度助成金

  研究期間 : 2024年04月 -2025年03月 

  代表者 : 伊佐田智規
• 海洋生態系解析のための SGLI 海色プロダクトの検証と改良

  宇宙航空研究開発機構（JAXA）：第3回地球観測研究公募 (EO-RA3)

  研究期間 : 2022年04月 -2025年03月 

  代表者 : 平田貴文, 平譯享, 伊佐田智規, 田中昭彦, 吉川尚, アイリーンアラビア, 佐藤恵子, 緒方一紀
• 北海道沿岸域の持続可能な水産業を目指した海洋圏プロダクトの検証および 複数衛星データを利用した海洋空間情報の開発

  宇宙航空研究開発機構（JAXA）：第3回地球観測研究公募 (EO-RA3)

  研究期間 : 2022年04月 -2025年03月 

  代表者 : 伊佐田智規, 谷内由貴子, 葛西広海
• 北海道厚岸湖のアマモ場における 透明細胞外重合物質粒子(TEPs)の変動要因の解明（その２）

  公益財団法人 国際エメックスセンター：令和5年度若手研究者活動支援制度助成金

  研究期間 : 2023年04月 -2024年03月 

  代表者 : 伊佐田智規
• 見逃されてきた陸海相互作用：海岸地すべりが沿岸生態系に与える影響の定量的評価

  日本学術振興会：科学研究費助成事業

  研究期間 : 2021年07月 -2024年03月 

  代表者 : 仲岡 雅裕, 伊佐田 智規, 土井 一生

   

  北海道東部沿岸域を対象に、海岸地すべりによる土砂供給が沿岸生態系に与える影響の評価を行う。この目的を達成するため、(1)広域（10 kmスケール） の海域における沿岸生態系の定期調査、(2)地すべり発生後の生態系の変化の集中的な観測、(3)地すべり調査定点における連続的な観測、(4)上記の結果を取り入れた流動・生態系動態統合モデリングを組み合わせた研究を行う。観測結果を取り入れたモデルを用いたシミュレーションにより、陸源物質の河川を介した影響と地すべりによる土砂供給の直接的影響の相対的重要性を明らかにする。本研究で展開する生態学分野と地質学分野の異分野協働研究は、防災と生態系・生物多様性保全という社会的なニーズの高い課題を統合的に扱うことを通じて、新たな学問分野の創設につながることが期待される。 初年度は、研究サイトの選定および研究方法の検討を進めた。研究サイトについては、厚岸湾内の仙鳳趾エリアに海岸地すべりの連続観測サイトを設けて、地すべり動態の観測を開始するとともに、バラサン岬～愛冠～アイニンカップのエリアにかけてもドローンによる定期観測サイトを設定して観測を開始した。ドローン撮影の手法についても検討を行い、海岸崖の周辺域を含む撮影エリアに対して異なる撮影角度で連続撮影をし、画像を合成することで海岸崖の変化および崖の下の透明度や藻類の繁茂状況を把握する方法を確定した。さらに、アイニンカップエリアにおいては、実際の海岸崖くずれに伴い変化した海底における海草類の分布の変化について観測を開始したところ、海底地形の変化に伴いオオアマモの分布が拡大するとともに種子繁殖にかかる形質の変化が生じていることも発見した。
• ドローンと船舶の同時観測で明らかにする河川水が沿岸域で駆動する物質循環

  日本学術振興会：科学研究費助成事業

  研究期間 : 2021年04月 -2024年03月 

  代表者 : 木田 新一郎, 田中 潔, 芳村 毅, 伊佐田 智規
• 北海道厚岸湖のアマモ場における 透明細胞外重合物質粒子(TEPs)の変動要因の解明

  公益財団法人 国際エメックスセンター：令和4年度若手研究者活動支援制度助成金

  研究期間 : 2022年04月 -2023年03月 

  代表者 : 伊佐田智規
• 北海道沿岸域におけるSGLI/GCOM-Cから得られる海洋圏プロダクトの検証

  宇宙航空研究開発機構（JAXA）：第2回地球観測研究公募 (EO-RA2)

  研究期間 : 2019年07月 -2022年03月 

  代表者 : 伊佐田 智規
• 厚岸沿岸域における春季・夏季・秋季植物プランクトンブルームの解明

  日本学術振興会：科学研究費助成事業

  研究期間 : 2019年04月 -2022年03月 

  代表者 : 伊佐田 智規

   

  本研究は、北海道東部の厚岸沿岸域における海洋環境と植物プランクトン群集組成の季節・経年変化を明らかした。主に北海道大学厚岸臨海実験所の桟橋前での高頻度観測、船舶による厚岸湾での時系列観測、および栄養塩添加ボトル培養実験を実施し、夏季、秋季に起こる春季よりも大規模な植物プランクトンブルームは、8月の寒流（沿岸親潮）から暖流（宗谷暖流変質水）への水塊交換に加えて、台風などの集中豪雨に伴う河川からの栄養塩供給が夏季ブルーム発生に寄与している可能性が示唆された。
• SGLI/GCOM-Cによって得られる沿岸域の固有および見かけの光学特性、植物プランクトン色素、純基礎生産力プロダクトの検証

  宇宙航空研究開発機構(JAXA)：地球環境変動観測ミッション（GCOM）第6回研究公募

  研究期間 : 2016年04月 -2019年03月 

  代表者 : 伊佐田 智規
• ハイパースペクトルデータを用いた沿岸域における植物プランクトン識別モデルの開発

  日本学術振興会：科学研究費助成事業

  研究期間 : 2016年04月 -2019年03月 

  代表者 : 伊佐田 智規

   

  広範囲の波長帯を連続的に測定できるハイパースペクトル分光データから，海洋における4種類（珪藻類，藍藻類，緑藻類，および渦鞭毛藻類）の植物プランクトン機能タイプ（Phytoplankton Functional Types, PFTs）の優占を識別可能とするPFT識別モデルを開発した．特に，2階微分分光スペクトル解析は，それぞれのPFTの識別精度を向上させる有用な手法であることが本研究により明らかとなった．また，植物プランクトンの光吸収係数のハイパースペクトルデータは，生物光学地理区を分類する有用なパラメータになりうることも本研究によって示唆された．
• 親潮域春季ブルーム期における植物プランクトン群集の光合成光利用特性と基礎生産力に関する研究

  公益財団法人日本科学協会：笹川科学研究助成

  研究期間 : 2008年04月 -2009年03月 

  代表者 : 伊佐田 智規