Community structure of benthic mollusca and its relationship with environmental factors in the mainstream of Huaihe River

The benthic mollusca community structure at eleven sampling sites in Huaihe River was investigated in March, June, September and December 2011. A total of 26 species from 9 families were recorded. Thereinto, only 3 species occurred in the first upriver site: Tongbaijinzhuang, and 15 species occurred in the downriver site: Xinchengkou. There were remarkable correlations between water depth and the number of species (r=0.617, P=0.043, n=11), and water depth and density (r=-0.654, P=0.029, n=11). Consequently, the number of species showed a certain increasing trend from upriver to downriver sites. The results of One-way ANOVA showed that there were insignificant seasonal variations in three biocenotic indices (Shannon-Wiener diversity index F(3, 40) =0.225, P=0.879, Margalef index F(3, 40)=0.902, P=0.449, and Pielou evenness index F(3, 40)=0.841, P=0.479) and biomass F(3, 40) =1.931, P=0.14, but not in density F(3, 40) =5.45, P=0.003. The mean maximal density (90.13 36.31) ind./m2 occurred in June while the minimum (14.42 2.78) ind./m2 appeared in December. different with the former, the mean maximal biomass (155.08 50.43) g/m2 occurred in September while the minimum (39.15 14.08) g/m2 appeared in March. The results of One-way ANOSIM showed that there was no remarkable seasonal change in mollusca community structure at density and biomass composition (both P 0.05). The average dissimilarity of density between months ranged from 53.87% to 59.12%, while from 58.76% to 68.58% in biomass. Redundancy Analysis (RDA) showed that river width, water depth and the type of substrate were the main environmental variables deciding the spatial distributions and species richness in Huaihe River.