Zooplankton Community Structure in Water Bodies of Southern Kazakhstan in Summer Season: Drivers, Bioindication, and Interannual Dynamics

The water bodies of southern Kazakhstan are under strong anthropogenic pressure, underscoring the relevance of their comprehensive research. In the summer of 2025, hydrobiological and hydrochemical studies were conducted at 32 stations across seven water bodies in the region. The dissolved solids content (TDS) ranged from 239.5 to 1472.5 mg/dm³, with favorable oxygen levels and relatively low nutrient levels. Zooplankton comprised 100 species, with rotifers predominating. Zooplankton abundance was 133.2–1289.9 thousand specimens/m³, with a biomass of 0.99–3.94 g/m³. The average number of species per sample varied from 11.5 to 26.7. The Shannon index values ranged from 1.20 to 2.74 bits. The average individual mass of a specimen varied from 0.0011 to 0.0371 mg. Cluster analysis revealed significant differences in the species composition of planktonic invertebrates across water bodies and their biotopes, which, according to the MDS analysis, reflected heterogeneity in external conditions. Analysis of multivariate data showed that the main factors shaping summer zooplankton community structure in the surveyed water bodies were TDS, silicon, and phosphate. The reasons for the identified dependencies between abiotic and biological variables are discussed. The high indicator significance of zooplankton communities in assessing the ecological state of aquatic ecosystems is demonstrated.