DISTRIBUTION OF SNAIL FROM THE GENUS GYRAULUS (GASTROPODA, PLANORBIDAE) IN THE MIDDLE TRIBUTARY OF THE SARATOV RESERVOIR
Authors:   Samara Federal Research Scientific Center RAS, Institute of Ecology of Volga River Basin RAS, Mikhailov R.A. 
Published: April 2024

Background.The Volga basin has been studied unevenly from an ecological point of view. The region of the Upper Volga can be rightly considered the best studied area. While the Lower Volga remains less investigated despite its significant influence on the complex of interrelated social, economic and ecological problems. The most informative assessment for the state of aquatic ecosystems is the state of macrozoobenthos which has various advantages over other approaches, first of all, consisting in species diversity and structure of bottom communities. Freshwater mollusks are one of their numerous groups. In the Volga basin there are representatives of two classes: Gastropoda and Bivalvia. Therefore, the aim of the work is to reveal the peculiarities of Gyraulusalbus distribution in the Samara River and to establish quantitative characteristics in different sections with different ecological conditions. Materials and methods. The study of malacofauna from the source to the river mouth was carried out in the Samara River. A total of 17 stations belonging to different sections were examined. Samples were taken during the low-water period. Near the shore, samples were collected using a hydrobiological scraper (blade length 0.2 m) and a quantitative frame. In deep water using Eckman-Burgey dredge (1/40 m2) with two replicates. The collected material was fixed with 95% ethanol solution, which was replaced with 70% after one week. Statistical processing was performed using Statistica 10.0, Microsoft Excel 2010 and in the R 4.0.5 programming environment and its vegan package. Results.SnailG. albus were recorded by us in sections of the river from its source to its mouth. Specimens of the species were recorded exclusively in the thickets of higher aquatic vegetation. Occurrence of the snail in the river biotopes was low and amounted to only 42% of all investigated stations. This is largely due to the natural rapid flow of water at most sites and hence the small area of macrophytes, which are important for the development of the species. The species prefers low-flow or standing water bodies, so the presence of a small reservoir on the river favored the quantitative indicators of the species in the river, reaching its peak just in this biotope. Morphological variability of the species' shells had no significant differences in the sections of the watercourse. The assessment of the influence of the most significant abiotic and biotic factors on the distribution of G. albus in the Samara River, fallen by the multivariate ordination method revealed three significantly correlated environmental variables: dissolved oxygen concentration, macrophyte area, and salinity level. Conclusions. The results of the study added to the existing gaps in the current composition and distribution of freshwater malacofauna in the region. A number of features of quantitative indicators reflecting features of G. albus habitat in conditions of lotic ecosystems were revealed.