Abstract: Based on the unstructured-grid finite-volume ocean model FVCOM (Finite Volume Community Ocean Model) coupled with the NPZD(Nutrient-Phytoplankton-Zooplankton-Detritus) model, this study develops an ecological model for the East China Sea to simulate nitrogen and phosphorus nutrients as well as phytoplankton dynamics in 2021. Combined extreme scenarios, including increased nutrient loads, decreased water transparency, and elevated sea surface temperature, are evaluated. Results indicate that the FVCOM-NPZD model can reproduce the annual seasonal variations of nutrients in the East China Sea and effectively capture the spatial distribution characteristics of phytoplankton in the region. Increased water transparency contributes to the reduction of nutrient concentrations downstream of the Changjiang Estuary and may enhance phosphorus limitation in the downstream area; elevated sea surface temperature alters the timing of phytoplankton bloom outbreaks and the seasonal characteristics of their spatial distribution. However, the capacity of the entire ecosystem to mitigate the intensification of nutrient loads is extremely limited. This study facilitates the understanding of ecosystem response characteristics under combined extreme conditions and provides a foundation for developing more complex ecological models for the East China Sea.

Key words: FVCOM-NPZD, East China Sea, ecological model, nutrients, combined extreme conditions