Zooplankton of the Brackish Lakes in Turan-Uyuk Basin (Republic of Tyva)

Abstract

The study addresses the species composition of zooplankton in five mineralized water bodies located in the Turan-Uyuk basin (Tyva). Lake Beloye is a regional natural landmark. In total, 36 species of 22 genera, 9 families, 4 orders were identified. Cladocera constitute 67 % of the species. The major species are Daphnia magna, Brachionus plicatilis, Daphnia pulex, Daphnia longispina, Megacyclops viridis, Ceriodaphnia reticulata, Chydorus cf. sphaericus, Simocephalus expinosus, Acanthodiaptomus denticornis, Arctodiaptomus baсillifer, Moina macrocopa, Keratella quadrata, Brachionus quadridentatus brevispinus, and Daphnia hyalina. The main abundant species in two lakes, Beloye and Arzhaan, is D. magna, which has been the dominant species in Lake Beloye for decades. The zooplankton of Lakes Beloye and Arzhaan include Macrotrix tabrizensis, a rare species, which is known to occur only in one Russian region – Tyva. Tretocephala ambigua lives in Lake Beloye. In the study period, we observed an increase in the abundance of zooplankton: by a factor of 6 in Lake Beloye and by a factor of 2 in Lakes Kisloe and Arzhaan. We believe that this is a consequence of an increase in organic load on water bodies, resulting from shallowing of the lakes and human impact. The occurrence of the species such as Moina macrocopa and Brachionus quadridentatus brevispinus, which inhabit water bodies rich in organic matter and have not been previously detected in the study lakes, confirms this assumption. Cladocerans, which have a high filtration capacity, remain dominant in Lakes Beloye and Arzhaan, and this is beneficial for the lakes. The increasing abundance of Brachionus plicatilis in Lake Kisloye performs a compensatory function in the processes of natural self-purification. At the same time, the fact that species rare for the fauna of Russia have been constantly found in the study lakes indicates the presence of favorable conditions for their development and life, which further increases the value of these unique natural environments