Benthic communities of saline rivers in the arid zone of south Russia: saliny tolerance, production, trophic conditions

The article presents the results of long-term studies (2008-2014 and 2017-2019, 2023) of macrozoobenthos communities and the trophic conditions for their development in six saline rivers of the Lake Elton basin, characterized by important stopovers sites of migrating waterfowl in Europe. The aim of the work was to study the salinity tolerance of macrozoobenthos species, identify their quantitative indicators in a wide salinity gradient and establish the long-term production dynamics of benthic invertebrates. During the studied period, within a wide range of river salinity, from 4 g l-1 to 114 g l-1, a decrease in macrozoobenthos species richness was established, from 87 species in mesohaline rivers to 30 species in polyhaline rivers and to 10 species in a hyperhaline river. The abundance, biomass and production of macrozoobenthos varied widely, mainly determined by the development cycles of common salinity-tolerant dipterans species. The production of macrozoobenthos in mesohaline and polyhaline rivers was comparable or higher than observed in brackish water lagoons in Europe. With increasing water salinity, a decrease in the average long-term macrozoobenthos production values during the summer period was observed. The production of macrozoobenthos increased from the middle reaches of the rivers towards their mouth reaches, which is explained by an increase in the production of hydrobionts of lower trophic levels. At the same time, an analysis of the variability of macrozoobenthos production in rivers with different salinity levels did not reveal a pronounced trend in the long-term series of observations.