Ecological Assessment of Zooplankton Abundance and Distribution in Hanjagi Lake, Vijayapura, India

Abstract

The present study investigated the seasonal dynamics of zooplankton diversity, density, and biomass in Hanjagi Lake, Vijayapura District, Karnataka, over one year (June 2024–May 2025). Zooplankton samples were collected seasonally from five stations by filtering 100 L of surface water using a 150 µm plankton net, and quantitative analysis was performed using Sedgwick–Rafter counting methods. A total of 27 genera belonging to five major groups were recorded, with crustaceans dominating throughout the study period. Zooplankton density ranged from 20 to 290 individuals L⁻¹, with peak abundance during the monsoon season and minimum values during summer. Biomass also showed marked seasonal variation, with wet weight ranging from 0.32 to 2.40 mg L⁻¹ and dry weight ranging from 0.12 to 0.88 mg L⁻¹, with the highest values during the monsoon. Diversity indices indicated moderate to high diversity and relatively uniform species distribution across stations. Seasonal fluctuations in density and biomass were closely associated with hydrological changes and environmental conditions. Overall, the findings suggest that monsoon-driven nutrient enrichment enhances zooplankton productivity, highlighting the ecological significance of seasonal dynamics in maintaining the stability and functioning of Hanjagi Lake.