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Changes in the relative abundance of diatoms and dinoflagellates have been attributed to anthropogenic climate warming and water eutrophication.We used observations from multiple cruises in the East China Sea(ECS)and generalized additive mixed models(GAMMs)to project the effects of warming and eutrophication on diatom and dinoflagellate biomass.Fucoxanthin(Cf)and peridinin(Cp)concentration were used as proxies of diatom and dinoflagellate biomass,respectively.The environmental data temperature,nutrient concentrations,total chlorophyll a,salinity,and MLD,as well as spatial(sampling station,depth)and temporal parameters(month)were used as explanatory variables.Our GAMMs accounted for 78.5%and 73.9%of the variation of loge transformed Cf and Cp,respectively.Model results showed the two pigments responded differently to temperature and N:P ratio,especially at higher levels.Nonlinear relationships indicate lower temperature and N:P ratio favor diatoms while higher temperature and N:P ratio favor dinoflagellates.Based on our model results,under a scenario for the year 2100 in which both temperature and loge transformed N:P ratio increased 2 units in the future,we predict that Cf could decrease in 68%of stations while Cp could increase in 97%of stations in the surface water of the ECS.Our model projects that mean Cf should decrease by 36%while mean Cp should increase by 13%in the surface water of the coastal ECS.