ZOOPLANKTON OF SALINE RIVERS IN THE ARID ZONE OF SOUTHERN RUSSIA (ELTON LAKE BASIN)

The zooplankton from six small rivers in the basin of Lake Elton with the water mineralization of 9-41 g/l was studied in August of 2008-2009. A total of 36 species from eight taxonomical groups were identified; they mainly belonged to halophilous and halobiontic complexes of organisms. In the lake basin, 11 species were recorded for the first time (Keratella tropica, Synchaeta pectinata, Euchlanis pyriformis, Bosmina longirostris, Ceriodaphnia setosa, Paracyclops fimbriatus, Cletocamptus confluens, Candona marchica, Limnocythere dubiosa, Apocyclops dengizicus, and Ischnura pumilio). The most numerous was the halobiont Brachionus plicatilis; in the polyhaline biotopes, its abundance reached 7 thousand ind./l at the biomass of 12 mg/l. The total amount of the zooplankton (the abundance is 0.1-7200 ind./l, the biomass from <0.01 to 12.2 mg/l) in the studied rivers was comparable to that in other saline rivers. In most of the rivers, the abundance of the zooplankton increased from their head to the mouth due to the mass development of one or two species. As the water mineralization became higher than 12 g/l, a sharp (by more than two times) decrease in the richness of the zooplankton, especially in the Rotifera, Cladocera and Ostracoda groups, was recorded. The effect of salinity and other environmental factors on the zooplankton is discussed.