Spring nekton community structure and its relationship with environmental variables in Hangzhou Bay-Zhoushan inshore waters

Hangzhou Bay-Zhoushan inshore waters are the home of many commercial fish species, providing a good place for spawning and habitats. The environments in these areas significantly affect the marine species and its structure. According to the bottom trawl survey, covering 80 stations, in these areas during spring, 2016, we studied the fish and macro-crustacean species assemblage and its spatial distribution. The canonical correspondence analysis (CCA) was used to reveal correlation between functional traits of fish and macro-crustacean species (abundance and size) and environmental variables. The results showed that all the marine species can be divided into five ecological groups (dominant group-Amblychaeturichthys hexanema, demersal fishes, pelagics, shrimp, and crab), with the average abundance 546, 213, 83, 316 and 15 individuals hour, respectively. The average size for these ecological groups was 0.29, 2.19, 4.96, 0.36 and 6.66 g/individual, respectively. According to five ecological group abundance, bottoms temperature, bottom salinity and surface turbidity, the waters were clustered into two areas: Hangzhou Bay and Zhoushan inshore waters. Abundance of most of the ecological groups significantly differed in two areas, while the size of most groups was not significantly different. As affected by the mixed waters of fresh water runoff and offshore waters, the large abundance of marine communities gathered in Zhoushan inshore areas, which was characterized by high primary production. The CCA analysis showed that environmental variables in the first two axes explained around 25% of the total variation of abundance, and only 11.7% of the total variation of the average size, indicating that the environmental variables played a more important role in explaining the spatial distribution of abundance than in explaining spatial distribution of average size.