Shifts in composition and co-occurrence patterns of the fish community in the south inshore of Zhejiang, China

Anthropogenic or environmental changes can impact not only the composition and diversity of fish communities but also their species interactions. However, our current understanding of changes in species interactions remains limited. In this study, we utilized the bottom trawling survey data from 2017 to 2020 to investigate the temporal shift of fish communities in the south inshore of Zhejiang through co-occurrence networks, species composition, and diversity analysis. Our findings indicated significant changes in the fish community in recent years, including a decrease in the number of dominant fish families, a shift in dominant species from medium-sized commercial fish to low-value small fish, a decline in relative biomass of fish resources, a loss of diversity and species co-occurrences, an increase in community modularity, and a decrease in community clustering. The changes in co-occurrence networks revealed the local decline or loss of keystone species critical to the functioning of the ecosystem and the fragmentation of the fish community in the south inshore of Zhejiang. We also found that despite the dominant species being the major component of the community, not all of them held central positions in the co-occurrence networks. Additionally, the high fishing intensity and stochastic environmental changes may have consistently negatively affected offshore fish communities. As a result, the resilience or function of the fish community under external disturbance threats was likely decreasing over time. It is imperative that ongoing monitoring and assessment are needed to expose the ecological impacts of a range of pervasive anthropogenic threats. Further measures should be taken to mitigate the negative impact of fishing or other disturbances on the coastal ecosystems are necessary. •An apparent loss of diversity and decline in the relative biomass of fish resources has occurred in the fish community.•The increase in modularity and decrease in clustering reveals the fragmentation of the fish community in recent years.•Dominant species did not always occupy central positions in the co-occurrence networks.•Measures to mitigate the negative impact of fishing or other disturbances on the coastal ecosystems are necessary.