Seasonal changes of community structure of fish and crustaceans in the adjacent waters of Shengsi Ma’an Islands

The sea area near the Ma'an Islands in Shengsi has complex natural conditions and is a spawning ground, feeding ground, and migration channel for many fish and crustaceans. In order to study the effects of environmental factors, seasonal fishing suspension and other factors on the seasonal dynamic succession of fish and crustacean community structure, based on the survey data of fish and crustacean swimmers in the adjacent waters of Shengsi Ma'an Islands in Zhejiang Province in four quarters of 2021, this study used One-Way analysis of variance (ANOVA), similarity percentage analysis (SIMPER) and non-parametric multivariate analysis of variance (PERMANOVA) to study the seasonal changes of the average resource density and average individual size of the two groups. RDA analysis was used to study the relationship between seasonal fishing ban and environmental change and the two taxa and their dominant species. The results showed that a total of 103 species were caught, including 53 species of fish, 50 species of crustaceans, and 5 species of dominant species including Harpadon nehereus, Coilia mystus, Trichiurus haumela, Larimichthys polyactis and Collichthys lucidus, and 3 species of crustaceans, including Oratosquilla oratoria, Portunustri tuberculatus, Charybdis japonica. There were significant seasonal differences in the community structure composition of fish and crustaceans (average resource density and average individual size), but there were no significant regional differences. The average density of fish and crustaceans increased from spring to autumn and then slowly decreased to winter, while the average individual size was the smallest in spring and larger in other seasons, especially in summer. The results of RDA analysis showed that fishing pressure was the main factor that significantly affected the seasonal variation of average resource density and average individual size of fish and crustaceans (RDA1), and the seasonal variation of functional characteristics of fish and crustaceans was closely related to fishing pressure and environmental factors caused by fishing bans. The study shows that fishing ban and environmental factors have a significant impact on the functional characteristics (number and individual size) of fishery ecosystems, and further research on long-term changes in functional characteristics needs to be further strengthened. The results of this study can provide scientific basis and reference for the evaluation of marine protected areas and the sustainable utilization of fishery resources.