Peculiarities of the Species Composition, Abundance and Biotope Distribution of Mollusks Fam. Sphaeriidae in Rivers with a Many Lakes in the Catchment Area (by the Example of Water Courses of the Onega Lake Basin)

Using the example of the rivers of the Onega Lake basin, the species composition of mollusks of the Sphaeriidae family, their abundance, biomass, and contribution to benthic communities in rivers with many lakes in the catchment areas were analyzed. Patterns of spatial distribution of species across biotopes and gradients of environmental variables were traced. 26 species of mollusks of this family were identified, among them European-Siberian species predominate. Most of the species of mollusks of the family Sphaeriidae found by us have wide ecological ranges and are found in water bodies of various types. It was found that the contribution of Sphaeriidae to the species richness and functioning of aquatic communities in rivers in the conditions of branched lake-river systems (Lake Onega basin) exceeds the values usual for rivers with a small number of lakes in the catchment area. Using the ANOSIM and PERMANOVA methods, it was proved that the species composition of rocky rapids and riffles, sandy rifts and soft bottom soils is different. Using the IndVal test, seven species were shown to have a statistically significant association with one of these biotopes, and four of them, with rocky bottoms of river rapids and riffles. Using the NMDS method, it was shown that the greatest changes in the species composition of representatives of Sphaeriidae are observed when environmental conditions change from small streams with slow current and brown water to large rivers with fast current and clear water.