Seasonal succession and spatial heterogeneity of the nekton community associated with environmental factors in Hangzhou Bay, China

Spatiotemporal variations of nekton communities in estuaries are closely associated with habitat quality and environmental shifts. However, the importance of environmental conditions in shaping the spatial heterogeneity and seasonal succession of nekton in Chinese estuaries has rarely been reported. We collected nekton seasonally between 2018 and 2019 from 10 sites in the semi-enclosed Hangzhou Bay (HZB) and investigated the spatiotemporal dynamics of the nekton assemblage structure. A wide taxonomic diversity was identified, including 57 taxa from 23 families (36 fish, 15 shrimp, and six crabs). The nekton was mainly composed of small coastal, nearshore, and estuarine species, dominated by Miichthys miiuy, Collichthys lucidus, Exopalaemon annandalei, and Palaemon gravieri. The nekton biomass and abundance distribution were higher in the upper and middle bay than in the lower bay. The year-round northeast–southwest front zone was high related to the high-value dense area of nekton. Diversity and evenness indices of nekton biomass were higher during July and October than January and April. The unstable and high variability of the nekton community composition was reflected in the species diversity indices, seasonal alternate index, and seasonal migration index. Significant differences were found between fauna clusters among seasons, revealing the relationship between the habitat adaptability of species and seasonal variation of water masses. The nekton assemblage structure and distribution pattern were predominantly correlated with seasonal variations in natural and anthropogenic factors. In this study, the observed effects of anthropogenic and natural stressors on the seasonal variation of the nekton community and density distribution in the estuarine-bay ecosystems provide new insight into fishery ecosystems and ecosystem functioning.