The surface distribution of the phytoplankton community was investigated in July 2009, 2010, 2011, and 2013 on the mid-shelf of the East China Sea (ECS), which is under the influence of Changjiang River Diluted Water (CDW) and the Kuroshio Current. This study, based on a CHEMTAX analysis of phytoplankton pigments, revealed a predominance of cyanobacteria and prochlorophytes in the eastern ECS, which is perennially under the influence of oligotrophic Kuroshio Surface Water. Towards the west, on the mid-shelf of the ECS, the composition of the phytoplankton community varied from year to year. Diatoms dominated in 2009 and 2013, when dissolved inorganic phosphate (DIP) concentrations were higher than during 2010 and 2011. During the latter two years, characterized as high-nitrate years, a mixed population of cyanobacteria, chlorophytes, and other groups was observed. Cluster analysis based on the phytoplankton community composition together with a PCA of shipboard hydrographic and nutrient data for all four years helped to confirm that the summer phytoplankton community structure of the ECS was regulated by the mixing of water masses and the variability of nutrient ratios within the CDW as it moved offshore. Our results show that elevated DIP concentrations in the CDW favor the growth of diatoms and dinoflagellates. The primary pathway for DIP inputs appears to be the upwelling of high-phosphate subsurface waters along the coast of China.
Phytoplankton community East China Sea Changjiang River Diluted Water Kuroshio Intermediate Water Phosphate limitation N:P ratio Interannual variations
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We would like to thank the captains and crews of T/V Nagasaki-maru for their support during the cruises. This study was supported by the JAXA GCOM-C project (for Joji Ishizaka) and JSPS KAKENHI grant number JP26241009 (to Takeshi Matsuno). The participation of J. I. Goes and H. do R. Gomes was supported by visiting professorships at Nagoya University and NASA grants NNX13AI29A and NNX16AD40G. The participation of Shengqiang Wang was supported by the Natural Science Foundation of Jiangsu Province (BK20150914).
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