<p>Based on bottom-trawl survey data collected in 2006–2020 in the Beibu Gulf of the South China Sea (SCS), we developed and calibrated a multispecies size-spectrum model for the coastal fishery ecosystem. We summarized the national official statistical data on domestic marine fisheries in the SCS based on the fishery statistical yearbooks of China and Vietnam. The real fishing effort of the neritic fishery in the SCS was evaluated by a comprehensive weighted score verify the accuracy of the model output results. The size spectrum of the marine fishery community in the BBG has been declining over the past 15&#xa0;years. The community has adapted to external disturbances to some degree, but there have been significant changes in its internal structure: the proportion of most species groups has become more even, the average trophic level has decreased, and many species have experienced individual body-size miniaturization. By comparing the simulated relative fishing effort with the calculated real fishing effort over time, the decline of BBG fishery stocks was shown to be mainly attributed to the increasing fishing pressure, while frequent climate events may affect the size or quality of the habitable environment, thereby disrupted the recovery of the community. Our data suggest that small community sizes and changed community structure caused by overfishing may weaken the resilience of the community to climate anomalies. The design of coastal fishery management in the BBG should dynamically adjust fishery-management strategies taking into account the status of the community and impacts of climate anomalies.</p>