Abstract:

During the seasonal investigation on the snail  community in the tributaries(TRIB),western basin(WB),middle basin(MB),eastern basin(EB),and culturing enclosures of Chinese mitten crab(〖WTBX〗Eriocheir sinensis〖WTBZ〗)(CEES)of Yangcheng Lake,Jiangsu province from Jan.2008 to Oct.2009,six snail species belonging to 5 genus,4 families were recorded,in which 〖WTBX〗Bellamya aeruginosa〖WTBZ〗 was predominant,and 〖WTBX〗Alocinma longicornis〖WTBZ〗 subdominant.The mean density and biomass of snails in Yangcheng Lake were 220±47 ind./m2 and 2331±469 g/m2,respectively,both of which didn’t display seasonal and yearly variations,but differed significantly spatially.The relatively larger density occurred in CEES and EB and the least in WB;the highest biomass was found in CEES,and the lowest in EB.The highest abundance of 〖WTBX〗B.aeruginosa〖WTBZ〗 appeared in CEES and the lowest in WB,while EB had the highest abundance of 〖WTBX〗A.longicornis〖WTBZ〗 followed by CEES,and TRIB and the other two basins possessed the extremely low values.The highest density and biomass of snails,specially of 〖WTBX〗B.aeruginosa〖WTBZ〗,in CEES suggested that the enclosure culturing of 〖WTBX〗E.sinensis〖WTBZ〗 couldn’t led to the decline of density and biomass of the snail communities,and this fact would be explained by throwin of snails(mainly 〖WTBX〗B.aeruginosa〖WTBZ〗)towards the culturing enclosures of 〖WTBX〗E.sinensis〖WTBZ〗.The stepwise regression analysis showed that among physical and chemical environmental factors only water depth could be used to explain the spatial variations of snail density and biomass,and the canonical correspondence analysis(CCA) indicated that 〖WTBX〗B.aeruginosa〖WTBZ〗 tended to occur at sites with higher concentration of chlorophyll a,while 〖WTBX〗A.longicornis〖WTBZ〗 and 〖WTBX〗Parafossarulus striatulus〖WTBZ〗 at sites with larger transparency