Multifactorial environmental and ecological gradients from hydrology and land-use reflect coordinated...

Coastal ecosystems are shaped by multifactorial gradients arising from hydrological regimes and land-use pressures, which orchestrate plankton biogeography and pollutant dynamics across spatial scales. However, the links between environmental forcing, plankton community structure, and organic pollutant bioaccumulation remain poorly understood in marine ecosystems. In this study, we explored how hydrology and land use together influence plankton communities and the accumulation of organic pollutants along 29 stations on Taiwan's southwestern coast. Integrating physicochemical parameters, plankton assemblages, and compound-specific pollutant profiles (PAHs: 684 ± 987 ng/g, PAEs: 60,373 ± 30,376 ng/g, APs: 2689 ± 1561 ng/g) revealed coordinated ecological-chemical interactions. Univariate and multivariate analyses-including cluster analysis, exploratory factor analysis, network analysis, redundancy analysis, and canonical correspondence analysis-revealed significant (p < 0.05) environmental and ecological gradients between northern and southern coasts. We identify two distinct ecological regimes: (1) hydrologically influenced northern sites dominated by Thalassiosira and crustacean larvae and eggs, exhibiting lower pollutant loads and nutrient-driven plankton stability; and (2) anthropogenically impacted southern sites characterized by Chaetoceros, copepods, and elevated pollutant bioaccumulation. Compound-specific drivers revealed that PAEs were modulated by zooplankton abundance and TN, APs by phytoplankton traits and TP, and PAHs by plankton biomass and SiO₂. These findings demonstrate that pollutant uptake is not merely concentration-dependent but emerges from ecological trait-nutrient-pollutant coupling shaped by environmental gradients in estuarine and coastal ecosystems. Overall, our findings advance ecological understanding of pollutant-plankton interactions and provide a foundation for developing bioindicator-based strategies to monitor and mitigate coastal pollution, while supporting urban planning in the anthropocene.