Species Composition of the Volgograd Reservoir Basin Rivers (the Yeruslan River)

The river network of the vast territory of the Lower Volga basin in the semidesert area of the Russian Plain belongs to the least studied tributaries of the River. Among the rivers of the left bank in this natural and climatic zone, the Yeruslan River is the most important one, which largely determines the ecological characteristics of the area. The article presents the data of long-term (2015–2017) studies of macrozoobenthos of the Yeruslan River (a tributary of the Volgograd Reservoir) are presented. For the first time the detailed composition of fauna including 148 species and taxa of higher systematic rank is given. The basis of the taxonomic composition of the river is formed by a complex of eurybiont species. The limnophilic taxa Limnodrilus hoffmeisteri, Polypedilum nubeculosum, Cladotanytarsus mancus and Paratanytarsus sp. have the highest frequency. These taxa are widely distributed in plain rivers of the Upper, Middle and Lower Volga basin. The vast majority of species recorded in the Yeruslan River are typically freshwater forms. In the observed water salinity gradient (0,235–1,42 g/l), the highest species richness of macrozoobenthos was observed in the range of 0,5–0,8 g/l. Under highly saline conditions (>1,2 g/l) there are mayflies Caenis robusta and Cloeon gr. dipterum, caddisflies Oecetis furva, dragonflies Ischnura elegans, mollusks Viviparus viviparus, ceratopogonids Sphaeromias pictus, oligochaetes Limnodrilus hoffmeisteri, Stylaria lacustris, Tubifex tubifex, chironomids Cladotanytarsus mancus, Cryptochironomus gr. defectus, Dicrotendipes nervosus, Glyptotendipes barbipes, Glyptotendipes glaucus, Polypedilum nubeculosum, Parachironomus varus, Paratanytarsus sp, Psectrocladius sordidellus, Tanytarsus pallidicornis, Tanytarsus sp. etc. These species should be classified as euryhaline taxa. The flat character of the Yeruslan River, characterized by low gradients of the river bed and low flow velocity, determines the development of limnophilic, lake-pond fauna of macrozoobenthos. Along with typical freshwater taxa, euryhaline groups of hydrobionts inhabiting areas where saline soils are drained by river waters are widespread. The contribution of rheophilic species to macrozoobenthos composition is negligible, which distinguishes bottom communities of the Yeruslan River from plain rivers of forest and forest-steppe natural-climatic zones of the Volga River basin.