Freshwater Gastropod Composition and the Key Environmental Determinants in Hulu Ganga and Ma Oya River Basins of Sri Lanka

The present study determined the distribution of freshwater gastropods in relation to several environmental variables, in two tributaries of the Mahaweli River, Hulu Ganga and Ma Oya in the Central Province of Sri Lanka. Pearson’s Correlation and a multivariate statistical technique, Canonical Correspondence Analyses (CCA) were used to explore the environmental variables responsible for the species composition. In total eight species of gastropods were recorded. The most influential factors for the four species recorded in Hulu Ganga were dissolved oxygen (DO), total dissolved solids, conductivity and elevation, whereas in Ma Oya they were pH, conductivity, DO and temperature. The results of CCA show that measured environmental variables explained 95.76% of the variation in gastropod abundance in Hulu Ganga, but only 60.63% was explained in Ma Oya. Hence, there may be other unmeasured environmental factor(s) that influence the diversity and distribution of gastropods in Ma Oya.