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Last Updated :2024/11/07

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Master

Affiliation (Master)

  • Field Science Center for Northern Biosphere　Aquatic Research Station　Akkeshi Marine Station

Affiliation (Master)

  • Field Science Center for Northern Biosphere　Aquatic Research Station　Akkeshi Marine Station

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Profile and Settings

Degree

  • Ph.D(Environ. Sci.)（Hokkaido University）

Profile and Settings

  • Name (Japanese)

    Isada

  • Name (Kana)

    Tomonori

  • Name

    201301033681981876

Alternate Names

Achievement

Research Interests

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

Research Areas

  • Life sciences / Aquaculture
  • Life sciences / Ecology and environmental science
  • Environmental science/Agricultural science / Environmental dynamics

Committee Memberships

  • 2022/04 - Today   Journal of Oceanography   Editor
  • 2020 - Today   Frontiers in Marine Science   Review Editor for Marine Biogeochemistry

Awards

  • 2009 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 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 2008 North Pacific Marine Science Organization (PICES) PICES BIO Committee Best Presentation Award (Oral)
     
    受賞者: 伊佐田智規

Published Papers

  • Shinichiro Kida, Kiyoshi Tanaka, Tomonori Isada, Tomohiro Nakamura
    Journal of Geophysical Research: Oceans 129 (1) 2169-9275 2023/12/27 [Refereed]
     
    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.
  • 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 2022/09 [Refereed]
  • Hyojin Ahn, Miho Ito, Naoko Kouchi, Kentaro Watanabe, Hiroya Abe, Tomonori Isada, Masahiro Nakaoka
    PeerJ 10 e13705 - e13705 2022/07/27 [Refereed]
     
    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.
  • Ryosuke Futsuki, Toru Hirawake, Amane Fujiwara, Hisatomo Waga, Takashi Kikuchi, Shigeto Nishino, Tomonori Isada, Koji Suzuki, Yutaka W. Watanabe
    Journal of Oceanography 2022/06/08 [Refereed]
  • 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 1568-9883 2022/05 [Refereed]
     
    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.
  • Tomonori Isada, Stanford B. Hooker, Yukiko Taniuchi, Koji Suzuki
    Journal of Oceanography 0916-8370 2022/02/23 [Refereed][Not invited]
  • 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 0916-8370 2021/10/23 [Refereed][Not invited]
     
    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.
  • Tomonori Isada, Hiroya Abe, Hiromi Kasai, Masahiro Nakaoka
    Frontiers in Marine Science 8 2021/10/11 [Refereed]
     
    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 [aCDOM(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 aCDOM(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 aCDOM(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 [aNAP(443)], phytoplankton [aph(443)], and aCDOM(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 (ZSD), aNAP(443), and aCDOM(443). Chl a concentration and aph(443) were not good indicators for predicting ZSD 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.
  • 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) 2072-4292 2021/09/01 
    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]).
  • Stanford B. Hooker, Henry F. Houskeeper, Raphael M. Kudela, Atsushi Matsuoka, Koji Suzuki, Tomonori Isada
    Continental Shelf Research 219 104357 - 104357 0278-4343 2021/04 [Refereed]
  • 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 Kovacˇ, 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 2020/03 [Refereed][Not invited]
     
    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.
  • Kazuhiro Yoshida, Hisashi Endo, Evelyn Lawrenz, Tomonori Isada, Stanford B. Hooker, Ondrej Prasil, Koji Suzuki
    ESTUARINE COASTAL AND SHELF SCIENCE 228 0272-7714 2019/11 [Refereed]
  • Yoshida, K., Endo, H., Lawrenz, E., Isada, T., Hooker, S.B., Pr{\'a}?il, O., Suzuki, K.
    Estuarine, Coastal and Shelf Science 228 2019
  • 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 0024-3590 2019 [Refereed][Not invited]
  • 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 2153-6996 2019 
    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.
  • K. Yoshida, H Endo, E. Lawrenz, T. Isada, S. B. Hooker, O. Prášil, K. Suzuki
    Estuarine, Coastal and Shelf Science 212 80 - 84 0272-7714 2018 [Refereed][Not invited]
     
    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.
  • 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 0272-7714 2017/03 [Refereed][Not invited]
     
    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.
  • 平譯享, 高尾信太郎, 鈴木光次, 西岡純, 渡邉豊, 伊佐田智規
    Oceanography in Japan 日本海洋学会 23 (3) 65 - 77 0916-8362 2017 [Refereed][Not invited]
  • Tomonori Isada, Toru Hirawake, Tsukuru Kobayashi, Yuichi Nosaka, Masafumi Natsuike, Ichiro Imai, Koji Suzuki, Sei-Ichi Saitoh
    REMOTE SENSING OF ENVIRONMENT 159 134 - 151 0034-4257 2015/03 [Refereed][Not invited]
     
    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.
  • Shintaro Takao, Takahiro Iida, Tomonori Isada, Sei-Ichi Saitoh, Takafumi Hirata, Koji Suzuki
    PROGRESS IN OCEANOGRAPHY 126 233 - 241 0079-6611 2014/08 [Refereed][Not invited]
     
    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.
  • Yuichi Nosaka, Tomonori Isada, Isao Kudo, Hiroaki Saito, Hiroshi Hattori, Atsushi Tsuda, Koji Suzuki
    JOURNAL OF OCEANOGRAPHY 70 (1) 91 - 103 0916-8370 2014/02 [Refereed][Not invited]
     
    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.
  • K. Suzuki, A. Hattori-Saito, Y. Sekiguchi, J. Nishioka, M. Shigemitsu, T. Isada, H. Liu, R. M. L. McKay
    BIOGEOSCIENCES 11 (9) 2503 - 2517 1726-4170 2014 [Refereed][Not invited]
     
    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.
  • 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 1054-3139 2013/11 [Refereed][Not invited]
     
    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.
  • Tomonori Isada, Takahiro Iida, Hongbin Liu, Sei-Ichi Saitoh, Jun Nishioka, Takeshi Nakatsuka, Koji Suzuki
    JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 118 (4) 1995 - 2013 2169-9275 2013/04 [Refereed][Not invited]
     
    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.
  • S. Nakada, Y. Ishikawa, T. Awaji, T. In, S. Shima, T. Nakayama, T. Isada, S.-I. Saitoh
    Hydrological Research Letters THE JAPAN SOCIETY OF HYDROLOGY AND WATER RESOURCES 6 47 - 52 1882-3416 2012 [Refereed][Not invited]
     
    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.
  • 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 1726-4170 2011 [Refereed][Not invited]
     
    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.
  • 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 0967-0645 2010/09 [Refereed][Not invited]
     
    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.
  • 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 0967-0645 2009/12 [Refereed][Not invited]
     
    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.
  • Tomonori Isada, Akira Kuwata, Hiroaki Saito, Tsuneo Ono, Masao Ishii, Hisayuki Yoshikawa-Inoue, Koji Suzuki
    JOURNAL OF PLANKTON RESEARCH 31 (9) 1009 - 1025 0142-7873 2009/09 [Refereed][Not invited]
     
    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 2009/08 [Not refereed][Not invited]
  • 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 [Not refereed][Not invited]
  • 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 0916-8370 2007/12 [Refereed][Not invited]
     
    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.

MISC

Association Memberships

  • Association for the Sciences of Limnology and Oceanography   THE OCEANOGRAPHIC SOCIETY OF JAPAN   Japan Geoscience Union   

Research Projects

  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2024/04 -2028/03 
    Author : 伊佐田 智規, 片岡 剛文, 芳村 毅
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2022/06 -2027/03 
    Author : 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
    Date (from‐to) : 2024/04 -2025/03 
    Author : 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)
    Date (from‐to) : 2022/04 -2025/03 
    Author : 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
  • Validation for ocean color products and development of marine spatial information using multiple satellite applications in the coastal waters of Hokkaido: toward sustainable management of fisheries resources
    Japan Aerospace Exploration Agency (JAXA)：Research Announcement on the Earth Observations (EO-RA3)
    Date (from‐to) : 2022/04 -2025/03 
    Author : Tomonori Isada
  • Dynamics of Transparent Exopolymer Particles (TEPs) in the eelgrass meadows of Akkeshi-ko estuary, Japan
    International EMECS Center：FY2023 Grants-in-Aid for young researchers
    Date (from‐to) : 2023/04 -2024/03 
    Author : 伊佐田智規
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2021/07 -2024/03 
    Author : 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。
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2021/04 -2024/03 
    Author : 木田 新一郎, 田中 潔, 芳村 毅, 伊佐田 智規
  • International EMECS Center：FY2022 Grants-in-Aid for young researchers
    Date (from‐to) : 2022/04 -2023/03 
    Author : 伊佐田智規
  • Japan Aerospace Exploration Agency (JAXA)：Research Announcement on the Earth Observations (EO-RA2)
    Date (from‐to) : 2019/07 -2022/03 
    Author : Tomonori Isada
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2019/04 -2022/03 
    Author : Isada Tomonori
     
    We investigated seasonal and annual changes in oceanographic conditions and phytoplankton community structure in the coastal waters of Akkeshi Bay, Japan to clarify the factors controlling summer blooms in this studied area. We also conducted (1) high frequency sampling of Chl a concentration and (2) the nutrient addition bioassay experiments at the pier of Akkeshi Marine Station (AMS). Massive phytoplankton blooms occurred during spring and summer every year, but diatom compositions were totally different between spring and summer because of the water mass exchanges from cold coastal Oyashio water (COW) to Modified- Soya Warm Current Water (M-SWCW). Additionally, we found the significant relationships between the amount of monthly integrated rainfall obtained from AMeDAS at Ohta and the monthly integrated Chl a concentration at the pier of AMS. These results suggest that summer phytoplankton bloom could be triggered by the nutrient supply from the wetland-influenced river discharge.
  • Japan Aerospace Exploration Agency (JAXA)：地球環境変動観測ミッション（GCOM）第6回研究公募
    Date (from‐to) : 2016/04 -2019/03 
    Author : Tomonori Isada
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2016/04 -2019/03 
    Author : ISADA Tomonori
     
    We developed the algorithm for identification of Phytoplankton Functional Types (PFTs) with optical hyperspectral data of phytoplankton absorption to better understand marine biogeochemical cycles and to accelerate its implications for ocean color remote sensing applications. We selected four PFTs (diatoms, cyanobacteria, green algae, and dinoflagellates) as target PFTs. Our results indicate that an optical hyperspectral data with a derivative spectroscopy/similarity index (SI) method is a promising approach to identify the dominance of each PFT in the ocean. Additionally, we found that derivative spectra of phytoplankton absorption coefficients could be a useful indicator of bio-optical provinces.
  • Photosynthetic features and primary productivity of phytoplankton during the spring bloom in the Oyashio region, northwestern subarctic Pacific
    Japan Science Society：Sasakawa Scientific Research Grant
    Date (from‐to) : 2008/04 -2009/03 
    Author : Tomonori Isada

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