The fauna and benthic communities of invertebrates of the Ural river within the Atuar steppe (Orenburg state nature reserve)

There are 70 species and forms in the composition of zoobenthos of the river Ural and in water bodies of its floodplain have been identified. Mayflies and chironomids are represented in various ways (13 and 12 species and forms, respectively). Caddisflies (10) and stone flies (7) are rich in species. Among other inverte-brates, bivalves (6) and gastropods (5), small-bristled worms (5), non-chironomid dipterans (4), leeches, crustaceans and dragonflies, bugs and beetles were recorded. On sandy-gravel-pebble soils is formed a zoobenthocenosis, dominated by the mayflies Ephoron virgo. They are accompanied by Chironomidae larvae. The biomass of the community varies between of 29.32-31.68 g/m2 with an abundance of 18.1-32.44 thousand ind./m2. In the coastal of the channel is formed a pelophilic zoobenthocenosis, the basis of it abundance and biomass are constituted by the small-bristle worms Limnodrilus hoffmeisteri. They are accompanied by mollusks Stagnicola palustris and mysids P. lacustris. The biomass of the pelophilic community is 13.68 g/m2 with a population of 15.45 thousand ind./m2. In floodplain water bodies are formed pelophilic zoobenthocenoses, the biomass of which varies in the range of 19.2-34.24 g/m2 with an abundance of 5.64-30.04 thousand ind./m2. Chironomid larvae constitute the base of the population. The biomass is composed by dragonflies Libellula sp., Chironomids, and mollusks Bithynia tentaculata.