Contrasting pollution responses of native and non-native fish communities in anthropogenically disturbed estuaries...

Understanding the influence of environmental pollutants on the assembly mechanisms of estuarine fish communities is vital for addressing conservation challenges in these biodiverse ecosystems. Although significant research has explored the toxic impacts of pollutants such as petroleum, heavy metals, and eutrophication on individual species and populations, their effects on community assembly processes and the differential responses of native versus non-native fish at the meta-community level remain inadequately understood. This study utilized environmental DNA (eDNA) metabarcoding to analyze fish community diversity across 28 subtropical estuaries in China, assessing how these pollutants affect community composition and assembly mechanisms. Results indicated that eDNA was 2.54 times more effective than traditional methods in species identification, while also enabling the detection of a higher number of non-native fish species and more diverse functional guilds within estuarine ecosystems. A significant distance decay pattern (p < 0.05) was observed among native fish, whereas non-native species exhibited non-significant patterns. Neutral and null models showed that non-native species had significantly higher migration rates (0.005939 vs 0.001757) and a greater contribution of stochastic processes (82.38 % vs 70.59 %) compared to native species. Additionally, distance-based redundancy analysis (db-RDA), variance partitioning analysis (VPA), and correlation analyses revealed that native species were strongly constrained by environmental factors, particularly oil, Hg, Zn, Pb, Cr⁶⁺, and NH₄⁺, while non^-native species displayed notable resilience to these pollutants. These findings highlight the potential for non-native species to disproportionately influence community dynamics and assembly through unrestricted random dispersal amid environmental disturbances. This research clarifies the contrasting ecological responses of native and non-native fish communities to anthropogenic pressures in estuarine environments, offering essential insights into ecosystem resilience and informing biodiversity conservation strategies in rapidly changing coastal ecosystems.