Mollusks of the genus Dreissena (Mollusca: Bivalvia) in periphytic communities of shore protection constructions in the downstream of Kaniv Hydroelectric Power Plant

Abstract

Introduction . Mollusks of the genus Dreissena are invasive species of Ponto-Caspian origin. These mollusks are typical members of periphytic communities in water bodies and watercourses in Ukraine. They are the ecosystem engineers, which significantly modify the life conditions for the other species of these communities. At the same time, these mollusks are influenced by anthropogenic factors, including hydro-construction. The construction and operation of hydroelectric power plants significantly changes the ecosystems of the rivers, where they are built. Changes occur both in the upstream and downstream. Although the downstreams are exposed to less destructive effects, these effects also need to be studied. This is especially important because these sites often have an environmental value. Periphytic communities are sensitive to these effects. Therefore, the study of the reaction to them of Dreissena, which is an important member of these communities, is so important. Purpose . The aim of the study was to find out the seasonal dynamics of the development of the Dreissena communities affected by the functioning of Kaniv Hydroelectric Power Plant in the downstream. Methods . The research was carried out on the Dnipro river section below Kaniv Hydroelectric Power Plant between the town of Kaniv and the village of Pekari. The samples of periphyton were taken on the stones of the shore protection constructions. They have been collected in November 2016 and from March to October 2017.The density and the biomass of Dreissena settlements have been counted on 1 m 2 of stone surface. For the estimation of correlation was used Pearson correlation coefficient. Results . The density of Dreissena in periphytic communities varied in the range of 64‑7041 ind./m 2 . The part of these mollusks in the overall density of the communities was 1.7-81.1%. The values of the biomass were 0,01-148,4 g/m 2 . The part of Dreissena in the total biomass was 0.01‑99.5%.It was detected that the Dreissena does not overwinter in the conditions investigated. But its settlements are restored every year due to the presence of permanent settlements in the Kaniv reservoir. In August, a clear negative correlation (r=-0.79, statistically significant at p>0.05) between the density of these mollusks and the distance from the dam was found (Fig. 1). Conclusion . Two species of Dreissena are an important part of periphytic communities of the shore protection constructions in the downstream of Kaniv Hydroelectric Power Plant. The more numerous is the species D. polymorpha, its part in the settlements is 76.5-100%, and D. bugensis is much less numerous. Due to significant daily fluctuations in water levels, Dreissena does not overwinter on these structures, so its settlements disappear in winter and are restored during the growing season. It is revealed that quantitative parameters of the Dreissena settlements in certain periods of the year can correlate with the distance from the dam of the hydroelectric power station.