The Effects Of Different Uses And Environmental Factors On Freshwater Snail Diversity In Lake Enclosed On Autumn

Freshwater snails suffer from the expanding economic development due to the overlook of their functions in aquatic ecosystem by human being. To understand the effects of different uses and environmental factors on freshwater snail community, annual investigation was conducted on four Lakes Enclosed on Autumn with different uses in Jiangxi Poyang Lake National Nature Reserve in2012, which based on the preliminary investigation that run in the littoral zone of Poyang Lake2011. Species composition, diversity index, size, density and biomass were studied and their differences were compared. Incorporated with physical-chemical and other biological factors of each Lake, the effects of different uses on freshwater snails were analyzed.The cumulative species numbers of the preliminary investigation was19and the species were C. chinensis (Gray), C. cathayensis (Heude), B. quadrata (Benson), B. purificata (Heude), B. aeruginosa (Reeve), A. polyzonata (Frauenfeld), R. auriculata (Von Martens), R. ovum (Heude), S. cancellata (Benson), O. hupeniis (Gredler), B. fuchsiana (Moellendorff), Bithynia sp., P. sinensis (Neumayr), P. striatulus (Benson), P. eximius (Frauenfeld), P. anomalospiralis (Liu), Parafossarulus sp., R. swinhoei (H. Adams), and R. auricularia (Linnaeus). The cumulative species numbers of the annual investigation was11and the species of Zhonghuchi Lake were B.aeruginosa, P. sinensis, P. striatulus, P. eximius, and B. fuchsiana; the species of Banghu Lake were C. cathayensis, B. aeruginosa, P. sinensis, P. striatulus, B. fuchsiana, R. auricularia, R. plicatula (Benson), and Polypylis hemisphaerula (Benson), the species of Dahuchi Lake were B. quadrata, B. purificata, B. aeruginosa, P. eximius, and B.fuchsiana; the species of Shahu Lake were B. purificata, B. aeruginosa, P. sinensis, P. striatulus, P. eximius, and B. fuchsiana. Zhonghuchi Lake, Dahuchi Lake and Shahu Lake possessed roughly the same species compositions, which were all collectors, while there are3species, belonging to Pulmonata, of shredder in Banghu Lake. The commonly dominant species of four Lakes were B. aeruginosa (Reeve) and B. fuchsiana (Moellendorff).The mean Shannon-wiener’s Indices of gastropods in Zhonghuchi Lake, Banghu Lake, Dahuchi Lake and Shahu Lake were0.36,0.32,0.08, and0.43, respectively. Difference of the index in different transect were vast. Lakes like Banghu Lake and Shahu Lake, which possessed abundant macrophytes, saw a sharp decline of the index after July due to the loss of macrophytes caused by flood. Whereas the index of Zhonghuchi Lake, which possessed the least macrophytes, saw a dramatically increase under the same flood after July. However, the index of Dahuchi Lake remained at a low level.The mean shell height, shell thickness and weight of the dominant species, B. aeruginosa and B. fuchsiana, in Dahuchi Lake were all higher than other Lakes, while the same size indexes of Banghu Lake were all lower than other Lakes. On the whole, the size of snails became smaller, and the percentage of species numbers and density of small snails became higher with the increase of macrophytes. On the contrary, the size of snails became larger, and the percentage of species numbers and biomass of large snails became higher with the decrease of macrophytes.The mean densities of gastropods in Zhonghuchi Lake, Banghu Lake, Dahuchi Lake and Shahu Lake were54.60±6.88ind/m2,77.16±11.97ind/m2,13.14±1.88ind/m2, and56.54±7.27ind/m2, respectively. And the mean biomasses of gastropods in these Lakes were39.19±5.49g/m2,12.58±2.11g/m2,16.33±2.57g/m2, and34.45±4.81g/m2, respectively. Overall, lakes with abundant macrophytes showed higher gastropods density than lakes with rare macrophytes, which is due to the positive effect of macrophytes on the density of small snails. However, lakes with rare macrophytes showed higher gastropods biomass than lakes with abundant macrophytes, which is due to the negative effect of macrophytes on the biomass of large snails.For the relationships between environmental factors and freshwater snails, results showed that water depth and phycocyanin content of blue-green algae were negatively correlated with the species richness and density of snails. Turbidity and pH were positively correlated with the snails’ density. The species richness of macrophytes was positively correlated with the species richness and density of snails, but the biomass of macrophytes was negatively correlated with the biomass of snails. Noteworthily, the effects of these factors on Bellamya aeruginosa and Bithynia fuchsiana tended to be contrary, indicating that there may be different effects of the same environmental factors on different species.To sum it up, different uses of Lakes Enclosed on Autumn might indirectly affect the freshwater snails by altering the environmental factors and macrophytes. On the other hand, different stocking species mediated by lake uses might have different impacts on freshwater snails by predation, which might lead to differences in species composition, size and standing crop.