We develop a hierarchical Bayesian model linking the abundance of individual phytoplankton species with over a decade (1995Á2011) of environmental data from the Cariaco Ocean Time Series Program in the Cariaco Basin, Venezuela, to characterize how phytoplankton respond to environmental forcing. Temperature, salinity, irradiance, and macronutrient concentrations account for 39% of the variation in log cell abundance across 67 species. Individual phytoplankton taxa varied widely in their response

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... to these environmental variables. A principal component analysis of the environmental response profiles clearly distinguishes the responses of diatoms and dinoflagellates to environmental forcing. Phytoplankton abundance primarily varied with temperature, pH, and irradiance, with salinity and macronutrient concentrations acting as secondary drivers. In the aggregate, our results demonstrate that environmental changes, whether short-term or a result of climate change, should be expected to have dramatic consequences on the taxonomic composition of phytoplankton communities.