The East China Sea (ECS) and the Southern Yellow Sea (SYS) ecosystem is undergoing dramatic changes, but the spatiotemporal patterns and forcing mechanisms of phytoplankton variations remain understudied. Phytoplankton lipid biomarkers are useful proxies for productivity and community structure changes, and they were measured in suspended particles of more than 81 sites from spring and summer of 2011 in the ECS and SYS. In spring, the concentrations of brassicasterol (4.7-127 ng L À1 ) and dinosterol (0.7-37 ng L À1 ) were markedly higher in the northern and central SYS, while C 37 alkenones (0-15 ng L À1 ) were detected at only seven sites in the ECS. In summer, brassicasterol (25.3-1178 ng L À1 ) and dinosterol (0-125 ng L À1 ) showed high values off the Changjiang River Estuary (CRE), while C 37 alkenones (0-410 ng L À1 ) had high values in the northwest and central SYS. The mean concentrations of the three lipid biomarkers in summer were 3 to 61 times higher than those in spring. Spatiotemporal patterns of biomarkers reveal higher ratios of diatom/dinoflagellate and diatom/haptophyte in higher productivity areas, off the CRE in summer and the northern and central SYS in spring. This study validates the applicability of brassicasterol, dinosterol, and alkenones as proxies of productivity and community structure of the three phytoplankton taxa: diatoms, dinoflagellates, and haptophytes. The results indicate that nutrients (in summer) and turbidity-induced photosynthetic available radiation (in spring) play important roles in regulating spatiotemporal variations of phytoplankton in the ECS and SYS.

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