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CHARACTERISTICS OF THE ZOOBENTHOS COMMUNITIES IN THE MOUNTAIN RIVERS OF THE YENISEI BASIN

А. В. Андрианова

Abstract

In 2015, zoobenthos communities in the river Yenisei (upper and middle course) and in its tributaries (rivers Abakan, Mana, Kan, Agul, Kungus) was studied. All watercourses are mountain rivers, in the bottom fauna of which lithoreophilic organisms predominate, populating stony soils in a large current, at low water temperatures and favorable oxygen conditions. In zoobenthos, 231 species of macroinvertebrates were found, widely distributed in the Palaearctic and Holarctic regions. Dominant complexes were characterized by variability with the distance from river sources. In the river Yenisei benthos species composition expanded from the upstream (48 species) to the lower reaches (69 species). In the upper reaches of the Yenisei (area 1 - from the Kyzyl city to the city of Shagonar) the core of the benthic communities was represented by mayflies, caddis flies and chironomids. Downstream (area 2 - from the dam of the Mainskaya hydro power station to the Abakan city) the determining factor for the formation of the zoobenthos structure was the abundance of phytocenoses, where the Baikalian amphipods Gmelinoides fasciatus dominated. In the zoobenthos of the Middle Yenisei (area 3 - from the dam of the Krasnoyarsk Hydroelectric Power Station to the mouth of the Angara River), the chironomids took the leading positions. The quantitative distribution of the bottom fauna in the Yenisei was characterized by low values in the upper reaches (612 ind./m2 and 4.2 g/m2) and high values in area 2 (5.5 thousand ind./m2 and 19.5 g/m2). In the middle course of the Yenisei in area 3, the density of benthic communities (2.8 thousand ind./m2 and 10.5 g/m2) is quite consistent with our earlier studies in the beginning of 2000s - 3.5 thousand ind./m2 and 10.8 g/m2. In the tributaries of the Yenisei, the benthos species composition is more diverse than in the Yenisei; maximum values were in the rivers Mana and Kan (110 and 103 species, respectively). Bottom communities are represented predominantly by chironomids and mayflies, in the river Kan caddis flies complemented the quantity. The quantitative distribution of the bottom fauna in the tributaries of the Yenisei was heterogeneous. The smallest abundance (577 ind./m2) was recorded in the river Abakan, that belongs to the basin of the Upper Yenisei. The maximum abundance (2.8 thousand ind./m2) was found in the river Mana flowing into the Yenisei above Krasnoyarsk (basin of the Middle Yenisei). In the Kan River, which flows into the Yenisei below Krasnoyarsk, the abundance of benthos is comparable to its tributaries Agul and Kungus (1.2?1.9 thousand ind./m2). The distribution of biomass in the studied water streams depended on the taxonomic structure of benthic communities. The maximum values (10.1 and 12.3 g/m2) were found in the rivers of the Middle Yenisei - Man and Kan, and are associated with the dominance of caddis flies. In the rivers Abakan, Agul and Kungus biomass on average did not exceed 8 g/m2, while the contribution of stoneflies is higher than in other rivers.

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