Seasonal shifts in fish assemblages and ecosystem structure in Lianzhou Bay revealed by coupling functional trait...

Climate change-induced extreme precipitation is amplifying seasonal hydrological variability in coastal bays and reshaping ecosystem functioning. Understanding these seasonal dynamics is essential for ecosystem-based management (EBM). Focusing on Lianzhou Bay, China, this study integrated functional trait analysis with Ecopath model to systematically investigate wet-dry seasonal variations in fish communities, trophic structure, and energy flow. We found that although fish diversity indices showed no significant differences (p > 0.05), fish functional composition shifted markedly. The proportion of planktivorous fish increased by 40.47% during the wet season, while the dry season was characterized by higher proportions of demersal, omnivorous, and benthivorous fishes. These functional shifts were consistent with changes in ecosystem energy pathways. The detrital food chain dominated during the dry season, whereas the planktonic food chain became more prominent in the wet season. This pattern was supported by the substantial increased macrobenthos biomass in the dry season, which enhanced detritus utilization (detritivory/herbivory ratio, D/H, increased by 79.19%) and facilitated more efficient energy transfer to higher trophic levels. In contrast, the elevated proportion of planktivorous fish in the wet season significantly enhanced the direct utilization of primary production by 35.09%. Ecosystem analysis further showed that the ecosystem of dry season exhibited larger system scale and higher maturity, with total system throughput, total biomass, and ascendency increasing by 19.54%, 84.52%, and 15.92%, respectively, whereas the wet season mainly showed greater resilience. The strong agreement between functional trait analysis and ecosystem modeling demonstrated the effectiveness of integration analysis in revealing seasonal ecosystem dynamics. This framework provided a robust scientific basis for adaptive ecosystem management and seasonal conservation of coastal ecosystems under increasing climate change.