Analysis on the Spatial Distribution of Bullacta exarata (Mollusca:Gastropoda:Atyidae) Population in Yangtze River Estuary,China

Bullacta exarata (Philippi,1848) is a favorite seafood and a tidal and economic seashell with high nutrition and edible value in South China.It can be found in the intertidal flats in China,Japan and Korean along the coasts of West Pacific Ocean B.exarata was one important biological resource which played an mportant role in the food chain of the tidal flat ecosystem as a consumer.Since late 1990s,the population ecology and toxicology of B.exarata had been partly studied along the coasts in Zhejiang,China,however,the spatial distrib ution had never been analyzed.Moreover,B.exarata had never been reported a gain up to now in the Yangtze River Estuary although it was first recorded forma lly in late 1980s B.exarata population in the Nanhui tidal flat and North Chongming Island in the Yangtze River Estuary had been investigated and analyzed by Taylorpower law,Iwaos patch regression and Morisita ind ex from May to June,2000.The results indicated that the B.exarata populati on distributed widely between the supratidal zone and subtidal zone of the inter tidal flats from south Chaoyang Farm to Luchao Port in Nanhui tidal flat and in North Hangzhou Bay,from Niupenggang Port to Puyu Port in North Chongming Island ,in North Changxing Island,Mi-and sub-Kiuduansha shoal in the Yangtze Rive r Estuary.It was shown that the natural B.exarata population distributed extensively with clumped and negative binomial distribution Morisita index (I)=2.61,P<0.01 theoretically.The regression equations of Taylor power law and Iwaos patch regression were lnS2=-0.7472+1.3484 lnx-(r2=0.8132,P<0.01,n=8) and m*=-1.005+1.076 6x-(r2=0.9936,P<0.01,n=8) respectively.The population densities at 8 sample sites in the Yangtze River Estuary (D7>D6>CPB>DZB>CYN>DZN CNB>CP) were greatly different significantly by the analysis of variance ［ANOV AF=42.52>F0.01(7,32)=3.26,P<0.01,which were resulted obviously from human activities,including land reclamation of tidal flats and environmental pollution,and different natural conditions between island and tidal flats.