Taxonomic Structure and Quantitative Indicators of Benthic Invertebrates of the Varvara Reservoir in the Kura Cascade

This review summarizes published information on the taxonomic structure and biomass distribution of macrozoobenthic communities in the Varvara Reservoir, Azerbaijan. This basin, the last link of the Kura cascade, is a unique ecosystem with an average shallow depth of 3-4 meters and an extensive Phytophilous vegetation cover of 89.9%. Modern literature emphasizes that macrozoobenthos are sensitive bioindicators in determining water quality and assessing ecosystem health, and that they respond rapidly to environmental stress factors. This review is based on published studies that reported systematic sampling of five major biotopes (lithophile, psammophile, pelophile, pelo-psammophile, and phytophile) within the Varvara Reservoir. According to the reviewed literature, 113 species and forms of invertebrates belonging to 22 systematic groups have been reported from the reservoir. Among these organisms, chironomid larvae constitute 38.1% of the species diversity with 43 species, providing absolute dominance in taxonomic terms. Mollusks constitute the dominant component of the benthic biomass and represent the principal biomass component of the ecosystem. In particular, Phytophilous biotopes cover a large part of the basin, forming both a safe shelter and an abundant food source for benthic organisms. Diurnal water level fluctuations and cold water flows associated with the operation of the Mingachevir HPP directly affect the stability and metabolic processes of benthic communities in the coastal zone. The species Paramysis lacustris and Pontogammarus robustoides introduced to the basin have successfully adapted to the ecosystem and qualitatively enriched the food base of important fish species. The results reveal the high biological potential of the reservoir. Collectively, the reviewed studies indicate the high biological potential of the reservoir and provide a scientific basis for sustainable water-resource management and fishery conservation. In addition, the impact of high population densities of Melanopsis mollusks on parasitological risks in the region was also assessed.