Microplastic transport reshapes estuarine population dynamics in the Yangtze River Estuary: A coupled physical-biological modeling study

Microplastic pollution is an increasing threat to estuarine ecosystems, yet its population-level consequences remain difficult to quantify because pollutant transport and biological responses are rarely integrated in a single framework. Here, we couple Lagrangian particle tracking and Eulerian diffusion with a spatially explicit trait-based reference population model to examine how microplastic exposure interacts with seasonal habitat suitability in the Yangtze River Estuary. Simulations reveal a persistent northeastward transport corridor that creates demographic cold spots and sharp population gradients across the estuary. Microplastic effects are strongly non-additive: the same contamination level causes larger population declines under favorable temperature-salinity conditions than under environmentally constrained seasons. Across sensitivity scenarios, annual mean population loss ranges from 7.56 % to 18.81 %. Despite this variation in magnitude, medium-exposure zones consistently account for 43.65 %–66.64 % of total loss, revealing a pronounced area-intensity trade-off in which broadly distributed moderate contamination outweighs localized hotspots at the ecosystem scale. These results show that ecological risk in estuaries depends on the spatial geometry of pollution and its overlap with suitable habitat, highlighting the need for management strategies that address contamination extent as well as peak concentration.