Stuty On Phytoplankton Assemblage In East China Sea

The phytoplankton assemblage in East China Sea (24°00’～32°00’N,120°00’～128°00’E) during four seasons (Spring,2011; Summer,2009; Autumn,2010; Winter,2009) was studied with Utermohl method, including the species composition, dominant species composition, distribution of cell abundance and relationship between cell abundance and environmental factors. The objective of this study was to understand the phytoplankton assemblage in ECS more comprehensively and provide fundamental information for relative ecological research.The results revealed that phytoplankton in ECS was mainly composed of Bacillariophyta and Pyrrophyta, with a few species belonging to Cyanophyta, Chrysophyta and Chlorophyta. Totally,356species (including18uncertain species) were identified in ECS. For Bacillariophyta, a total of242species (including14uncertain species) belonging to70genera were identified. For Pyrrophyta, a total of104species (including3uncertain species) belonging to26genera were identified. The species number of autumn2010ranked first, followed by summer2009and spring2011, and the species number of winter2009ranked last. The ecotype of phytoplankton species in ECS could be approximately divided into cosmopolitan, tropic and warm temperate, with tropic speices predominating over warm temperate species in number.In the survey area next to Changjiang estuary, there broke out a Prorocentrum dentatum bloom in spring2011and a Chaetoceros debilis bloom in autumn2010. Through comparison, we found that in Pro. dentatum bloom, species diversity was low and cells mainly concentrated in the surface water, while in Cha. debilis bloom, species diversity was high and cells distributed evenly in different depths of water.The composition of dominant species varied among seasons. In spring, dominant species were Pro. dentatum, Paralia sulcata, Pseudo-nitzschia delicatissima and Thalassionema nitzschia, In summer, dominant species were Tha. nitzschia, Pse. pungens, Tha. frauenfeldii and Skeletonema sp.; In autumn, dominant species were Cha. debilis, Cha. curvisetus, Pse. delicatissima and Leptocylindrus danicus, In winter, dominant species were Par. sulcata, Tha. nitzschia, Pse. delicatissima and Tha. angstii.The distribution of cell abundance in ECS varied among seasons. In spring, high value of cell abundance appeared in area adjacent to Changjiang estuary. In summer, high value appeared in Changjiang estuary and the sea northeast of Taiwan Island. In autumn, high value appeared in the sea northeast of Changjiang estuary and the sea northeast of Taiwan Island. In winter, cell abundance was obviously lower than the other three seasons and no high value appeared in ECS.The CCA analysis between phytoplankton cell abundance and environmental factors revealed that different composition of dominant species in four seasons in the survey area was mainly induced by the complexity and alteration of water masses.