Impact of water salinity on long-term dynamics and spatial distribution of benthic invertebrates in the Small Aral Sea

In 1996–2008, macrozoobenthos of the Small Aral Sea was investigated. A total of 320 macrozoobenthos samples were collected. Statistical analysis and statistical mapping were performed using Statistica and Photoshop software. Ten taxa of macrozoobenthos were identified, with an average water salinity of the Small Aral Sea ranging from 6.3 to 19.0 PSU. Average annual community abundance reached 1962 specimens m⁻², with biomass of 107.1 g m⁻². Quantitative variables of macrozoobenthos decreased by an order of magnitude by the end of the analyzed period. The polychaete Hediste diversicolor and mollusks Abra ovata, Cerastoderma glaucum, Caspiohydrobia sp. were the dominant taxa. Statistical mapping and correlation analysis revealed that the high biomass of A. ovata and Caspiohydrobia sp. occur in areas with high water salinity. Aggregations of the mollusk C. glaucum were observed in various areas of the sea. The polychaete H. diversicolor preferred areas with relatively low salinity. Analysis of the results showed that the optimum salinity gradient with Aral salt composition was 17–27 PSU for A. ovata, Caspiohydrobia sp. and C. glaucum, while 1–27 PSU for H. diversicolor. Along with changes in water salinity, the currently growing pressure from freshwater fish is an additional factor affecting the structure of benthic communities in the Small Aral Sea.