Spatial and seasonal patterns of taxonomic, functional, and phylogenetic diversity of fish assemblages in island waters of Zhejiang, China: associations with environmental, climatic, and socioeconomic factors

Fish assemblages are important participants in regulating biogeochemical cycles and maintaining the health of island ecosystems. However, studies that analyze the diversity of fish assemblages in China’s island waters are scarce. In this study, we evaluated the taxonomic, functional, and phylogenetic diversity of fish assemblages around eight islands using 11 diversity indices, and explored the effect of human activity and natural factors on fish assemblage diversity via structural equation modeling (SEM). Results showed that three types of diversity exhibited significant differences among islands, the northern islands had highest values, followed by the southern, and the central was lowest. The environmental factors affecting the three types of diversity were varied, and the main factors regulating fish assemblages in spring and autumn were also different. Based on the SEM analysis, marine environmental factors exhibited a positive relationship with fish assemblage diversity (0.675), whereas socioeconomic factors demonstrated a negative relationship (-0.173). Furthermore, climate factors were associated with a reduction in fish assemblage diversity via indirect mechanisms (-0.456).SEM revealed that marine environment factors impacted fish assemblage diversity positively and directly, with a high path coefficient of 0.675. Socioeconomic factors exerted direct negative effects on fish assemblage (-0.173), while the influence of climate factors was indirect and negative (-0.456). These findings provided a comprehensive picture of fish assemblage diversity around Zhejiang islands and could facilitate the conservation and restoration of fish assemblages.