Ecological valence of a mollusk of the genus Radix in the middle river of the Lower Volga

Institute of Ecology of the Volga River Basin of the Russian Academy of Sciences, Togliatti, Russia Background. The Lower Volga basin has undergone significant changes caused by the development of human economic activity. However, its high significance in terms of assessing and preserving the biodiversity of natural complexes on the territory is very relevant. Small and medium-sized tributaries support the vast biodiversity of the flora and fauna of the Lower Volga and their transformations in the landscape of catchment areas and the hydrological regime create prerequisites for changing the entire natural complex of the region. The assessment of the state of rivers based on macrozoobenthos indicators has various advantages over other approaches, primarily in the species diversity and structure of bottom communities that reflect the state of the ecosystem over a long period. One of the important components of the benthic groups are mollusks as representatives of one of the most numerous animal species. Representatives of malacofauna form part of the food chain in the transmission of energy, are part of the diet of various species of fish and waterfowl. Therefore, the aim of the work is to study the distribution and features of quantitative indicators of Radix (Radix) auricularia (Linnaeus, 1758) under the influence of abiotic and biotic environmental factors in the Samara River. Materials and methods. The study was conducted in the summer of 2017 in the Samara River from the source to the mouth. Cameral processing was carried out, where their species identity was established, quantitative indicators were calculated, including morphometric measurements of shells. The environmental assessment was carried out using modern statistical methods. Results. Mollusk individuals were found in various biotopes of the river, characterized by a variety of abiotic and biotic conditions. The occurrence of the species in the river was 65%, with the highest registration at the stations of the lower course. The quantitative indicators varied significantly at different stations. The highest values of abundance and biomass were recorded in the small reservoir of the upper current. Analysis of changes in the morphometric characteristics of the shells of the species in different parts of the river allowed us to identify the largest individuals in the lower reaches, where the greatest anthropogenic impact on the water quality in the river. Thus, the changes caused by humans had less impact on the mollusk than the absence of natural favorable environmental factors. The assessment of the influence of various environmental factors on the mollusk R. (R.) auricularia allowed us to establish significant environmental variables of the environment. Conclusions. The presented results significantly supplement the available data on the biology and ecology of the mollusk R. (R.) auricularia in the region. All the extensive material made it possible to better understand the biotic preferences of the species in rivers under various environmental conditions. The results will make it possible to more effectively assess the state of inland water bodies with similar abiotic and biotic conditions.