COMMUNITY STRUCTURE OF CRABS AND ITS RELATIONSHIP WITH ENVIRONMENTAL FACTORS IN ZHEJIANG COAST AREA IN SPRING AND SUMMER

The coastal waters of Zhejiang Province that contain lots of islands and the water exchange fully in this area were affected by the Yangtze River diluted water, Taiwan warm current, coastal water of Jiangsu Province and the Yellow Sea cold water mass. It was the spawning and feeding grounds of multitudinous crabs because of abundant nutrient salts and food organisms. The crab resources and distribution and community ecology in the East China Sea have been reported since 1990s but mostly concentrated in the sea that was out of the 30 m’s isobath and reported before 2008. Thus, these studies cannot represent the characteristics of crab community in the whole coastal waters of Zhejiang Province due to the small research areas relatively. The current study analyzed the content of coastal crab community including species composition, floristic feature, dominant species, distribution of the resource density, species diversity and the relationship between the community structure and the environmental factors based on the fishery resources in Zhejiang coastal area in 2015 designated survey data using ecosystem diversity indexes, abundance/biomass comparison curve (ABC curve) and canonical correspondence analysis (CCA). The 28 captured crab species were belong to 11 families and 19 genera that were dominated by warm water species with a 78.57%. The dominant species were Charybdis bimaculata, Portunus trituberculatus and Charybdis japonica in spring and Portunus trituberculatus and Charybdis bimaculata in summer. The average resource density was 244.38 and 585.60 kg/km² in spring and summer respectively, and the density of middle-north Zhejiang coast area was higher than that of the south part. The average values of species abundance index (D), species diversity index (H′) and species evenness index (J′) were not related, indicating a low crab community diversity. According to the abundance/biomass comparison curve (ABC curve), crab community in spring and summer was seriously and moderately disturbed respectively. The result of Canonical Correspondence Analysis (CCA) analysis showed that the depth of water was the primary environmental factor regulating the distribution of crab community in all 9 environmental factors, and the salinity was the secondary environmental factor. These results enrich the basic information of crab species diversity in China’s coastal waters, which hold a useful scientific significance for understanding the dynamic changes of crab diversity in Zhejiang even the East China Sea. At the same time, it can provide reference for the establishment of marine ecological and environmental protection measures in offshore of Zhejiang Province.