Seasonal variation in the community structure of large benthic animals in the Crassostrea hongkongensis farming area, Donghai Island

The present study investigated the seasonal variation characteristics and ecological quality of macrobenthic communities in the Crassostrea hongkongensis culture area of Donghai Island, and analyzed the effects of oyster farming activities on the benthic ecosystem. Seasonal surveys of macrobenthos were conducted at 12 sampling stations in the coastal oyster farming area of Donghai Island from April 2025 to January 2026, covering spring, summer, autumn, and winter. Community structure and ecological environmental quality were comprehensively evaluated using diversity indices, principal component analysis (PCA), AMBI, and M-AMBI indices. A total of 90 macrobenthic species belonging to eight major taxonomic groups were recorded in the study area. Mollusca and Arthropoda were the dominant groups, accounting for 46.67% and 26.67% of the total species number, respectively. Species richness was highest in autumn and lowest in winter. The total biomass reached its highest value in spring (2 346 g/m²), which was significantly higher than that in the other seasons. The Shannon-Wiener diversity index was highest in autumn and lowest in winter. Dominant species showed obvious seasonal succession patterns, with the annelid Perinereis aibuhitensis dominating in spring and summer, while mollusks became dominant in winter. The AMBI and M-AMBI assessment results indicated that the overall ecological quality of the study area ranged from moderate to good, with the best ecological condition occurring in autumn, whereas the ecological quality at some stations declined in winter. Oyster farming activities increased habitat complexity and maintained the stability of certain dominant groups by providing attachment substrates and increasing organic matter input; however, they may also lead to local simplification of community structure and reduced biodiversity. These findings provide a theoretical basis for ecological protection and sustainable management of oyster farming areas.