The species composition and distribution of lithofacies seashells(Mollusc) in the intertidal zone of Zhejiang coast

Two sites were selected respectively in Wenzhou,Taizhou,Ningbo and Zhoushan,and the shellfish samples were collected on the intertidal rocky shores in Apr.and Oct.2009.The research contents included the species composition and distribution of lithofacies seashells (Mollusc) .During this survey,26 species of seashell were identified,belonging to 3 classes,11 orders,16 families,22 genera.In spring,the area of high biomass was the 8th sampling site(499.11 g/m2) ,the area of high density was the 3rd sampling site(145.67 ind/m2) ,low biomass and low density located in the 1st station(31.96 g/m2,36.92 ind/m2) .In fall,high biomass and high density points were distributed in the 8th station(206.82 g/m2,93.00 ind/m2) ,low biomass and low density were still in the 1st sampling site(26.92 g/m2,38.91 ind/m2) .Dominant species of shellfish were Thais clavigera Kuster,Barbatia obliquata (Wood) ,Septifer virgatus (Wiegmann) and Nerita albicilla Linnaeus by using combination of biomass and density as the index of dominant species.Seasonal evolution was remarkable.The biomass and density were higher in spring than these in fall.It can be obtained by analyzing air temperature,water temperature,ocean currents and environmental factors.With the water temperature increasing in spring,a large number of the shellfish move from the subtidal zone to the intertidal zone,so the density was higher in spring than in autumn owing to water temperature decreasing,predation,natural mortality and other factors.In addition,the biomass and density were the highest in 8th station,because it was protected by National Marine Nature Reserve Zone.And the shell height (length) of the dominant species was also relatively the highest in all stations.The resources of the 1st station were meager due to excessive catch.