Assessment of Zooplankton Community Structure and its Environmental Correlations in Khajikotnoor Reservoir, Kalaburagi, Karnataka

Zooplankton populations are vital indicators of freshwater ecosystem health and form critical links in aquatic food webs. This investigation examined the seasonal patterns of diversity, abundance, and species composition of zooplankton in Khajikotnoor reservoir, situated in Khajikotnoor village, Kalaburagi District, Karnataka. Monthly samples were drawn from each of four predetermined sites between January 2024 and December 2024, using standard 64 µm plankton nets. Species were analyzed by light microscopy and standard taxonomic guides. A total of 26 species were identified, distributed among four taxonomic groups: Rotifera (10 spp.), Cladocera (8 spp.), Copepoda (5 spp.), and Ostracoda (3 spp.). Rotifers were the most species-rich group, contributing 38.5% of the overall species total. Community composition showed highly significant seasonal variation (p < 0.001), with especially pronounced differences between the pre-monsoon and monsoon seasons. Shannon-Wiener diversity ranged from 2.14 to 3.42, with the higher winter values (H’ = 3.42 ± 0.18) indicative of increased evenness. These findings indicate that Khajikotnoor reservoir hosts a diverse and seemingly stable zooplankton assemblage, a condition that suggests the reservoir is currently functioning in a healthy ecological state. Nonetheless, existing and future pressures from nearby human activity and possible nutrient loading signal the necessity for continued monitoring. This study establishes a critical reference point for future investigations into the reservoir’s limnology.