Under climate change, variations in the hydrodynamic environment and nutrient conditions of the East China Sea may substantially affect phytoplankton community structure and their future evolution. This study selects three representative regions—the Changjiang Estuary, the mid shelf, and the Kuroshio-influenced eastern region—to characterize phytoplankton community structures across the shelf. A coupled physical–ecological framework is developed by integrating the General Ocean Turbulence Model (GOTM) with SPEAD ECS, an East China Sea application of the Simulating Plankton Evolution with Adaptive Dynamics model.First, reanalysis data for the present climate and CMIP6 future climate scenarios are used to drive GOTM to calculate temperature, mixed-layer depth, and vertical turbulent diffusivity (Kz) under present-day, mid-century, and end-of-century conditions. The results indicate that vertical mixing in the three representative regions of the East China Sea exhibits pronounced regional differences. In the shallow Changjiang Estuary, winter mixing can affect the entire water column, whereas in the mid-shelf and the Kuroshio-influenced eastern region, it reaches the depths of ~80 and ~120 m, respectively. In summer, the mixed layer shoals to about 10 m depth in all three regions, reflecting strong seasonal variability under the combined influence of hydrodynamics and atmospheric forcing.  Under future climate conditions, across all three regions, the summer stratified season becomes longer with earlier onset and later demise due to warming, while wintertime mixing becomes stronger primarily due to enhanced winds.Subsequently, the temperature, photosynthetically active radiation, and Kz are incorporated into the SPEAD ECS model to simulate annual cycles of nutrients, phytoplankton biomass, and dominant functional traits under different climate backgrounds. The preliminary results show the model successfully captures the first-order characteristics and changes in phytoplankton community structure: (1) a decrease in size towards offshore from the Changjiang Estuary to the Kuroshio-influenced eastern region; (2) vertical distributions of phytoplankton biomass strongly influenced by light availability, coupled with seasonal delivery of nutrients at the base of the euphotic layer; and (3) a slight decrease in biomass but mild increases in production, uptake, and grazing, and an overall community shift toward higher optimal temperature.At present, the ecological model considers only the limitation imposed by dissolved inorganic nitrogen.This study offers a coupled physical–ecological framework for projecting future changes in spatial patterns of phytoplankton community structures and cross-shelf ecological differentiation in the East China Sea under climate change.

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