Variations In Crab Community Structure And Species Diversity In Zhoushan Ashing Ground And Adjacent Waters

In this paper, we analyzed the species composition, quantitative distribution,community structure and the biodiversity of crabs in Zhoushan fishing ground and itsadjacent waters, referring to the crab data from the comprehensive investigation ofmarine ecosystem between August2006and November2007. Results showed thatthere are43species of crabs being identified in this survey area, belonging to10families and21genera. According to the calculation of IRI (the Index of RelativeImportance), the main dominants are Ovalipes punctatus, Charybdis bimaculata andPortunus trituberculatus, and they occupy90.65%of the total crab catch. The maindominants, plus Charybdis japonica, Portunus sanguinolentus and Matuta planipes,however, account for94.58%of the total catch. The average catch rate of crabs in thisarea is18.86kg/h, and the seasonal variations of catch rates are that: highest inautumn (33.29kg/h), then summer (20.15kg/h) and winter (15.18kg/h), lowest inspring (6.45kg/h). The concentrated areas of high catch are in the north of Zhoushanfishing ground and the Yangtze estuary fishing ground.Cluster analysis showed that the crab community of Zhoushan fishing groundcan be divided as Group Ⅰ, Group Ⅱ, Group Ⅲ. The seasonal differences duringthree groups are significant, characteristic species and discriminating species of threegroups in different seasons are all the same: Ovalipes punctatus, Portunustrituberculatus, Charybdis bimaculata. Just because of the differences in thecomposite proportion, these groups separate from each other. The spatial distributioncenters of crab catch are as follows (from west to east): Charybdis japonica, Portunustrituberculatus, Charybdis bimaculata, Portunus sanguinolentus, Ovalipes punctatus.Besides, these centers don’t overlap, they disperse in horizontal distribution.Simper analysis indicated that, in the all four seasons, Charybdis bimaculata,Portunus trituberculatus and Ovalipes punctatus are the main characteristic species,while the discriminating species include Ovalipes punctatus, Portunus trituberculatus,Charybdis bimaculata, Portunus hastatoides, Charybdis japonica, etc.The species richness indexes (D), Shannon-Wiener diversity indexes (H′), and the evenness indexes (J′) reveal to be low in Zhoushan fishing ground. Range ofseasonal diversity changes is not wide, and the diversity indexes are higher in autumnand winter.