Nutrient thresholds drive nonlinear shifts in estuarine macrobenthic functional traits: Implications for...

As transitional zones between land and sea, estuaries persistently receive terrigenous organic pollutants, potentially triggering nonlinear regime shifts in ecosystems and restructuring the composition and functioning of macrobenthic communities. This study synthesizes ecological data (2013-2019) to evaluate the responses of 11 functional traits and 5 functional diversity indices to environmental stress using multivariate analyses within a functional threshold framework. The results demonstrate that macrobenthic organisms adapt to environmental pressure through synergistic mechanisms of trait combinations, with nitrate nitrogen, ammonia nitrogen, phosphate, suspended solids and the eutrophication index identified as key drivers reshaping community functional structure. With increasing organic pollution, sensitive traits underwent unidirectional replacement by pollution-tolerant traits, leading to significant declines in functional richness (FRic), functional dispersion (FDis), and Rao's quadratic entropy (RaoQ). The stability of functional evenness (FEve) and functional divergence (FDiv) reveals the buffering effects of trait compensation against systemic collapse. Our trait-based threshold framework reveals how macrobenthos respond to multiple stressors. It identifies critical points of functional decline. These findings provide key intervention targets for managing estuarine organic pollution.