Seasonal Dynamics and Ecological Assessment of Zooplankton Community Structure in Baratagi Lake, Vijayapura, Karnataka, India

Abstract

Background: Zooplankton play a crucial role in freshwater ecosystems by linking primary producers to higher trophic levels and serving as sensitive bioindicators of environmental change. However, increasing anthropogenic pressures and eutrophication in lentic water bodies threaten zooplankton diversity and ecosystem stability, highlighting the need for systematic ecological assessments. Aims: The study aims to assess the seasonal dynamics, community structure, biomass, and ecological status of zooplankton in Baratagi Lake, Vijayapura District, Karnataka, India. Study Design: A one-year longitudinal ecological study. Place and Duration of Study: The study was conducted Baratagi Lake, Tikota Block, Vijayapura District, Karnataka, India, from June 2024 to May 2025. Methodology: Zooplankton were sampled seasonally from five stations during monsoon, post-monsoon, winter, and summer. For quantitative estimation, 100 litres of water were filtered using a plankton net (150 µm mesh size). Samples were preserved in 4–5% formalin and analysed using a Sedgwick–Rafter counting chamber. Abundance was expressed as individuals per litre. Wet and dry biomass (mg/l) were measured. Community structure was evaluated using Shannon–Wiener diversity index (H), Margalef richness index (d), and Pielou’s evenness index (J). Results: Sixteen genera representing five major groups were identified. Crustaceans dominated throughout the study (72–80%), followed by rotifers (12–20%), protozoans (4–6%), nematodes (1–2%), and others (2%). Total zooplankton density ranged from 10 individuals per litre in summer to 160 individuals per litre in monsoon. Wet biomass varied from 0.20 to 2.10 mg/l, and dry biomass ranged from 0.07 to 0.74 mg/l, with higher values recorded during monsoon and post-monsoon. The Shannon diversity index ranged from 0.52 to 1.27, richness from 1.45 to 4.95, and evenness from 0.861 to 0.965. Conclusion: Seasonal hydrological variation strongly influenced zooplankton abundance and diversity. Higher productivity during monsoon reflects favourable ecological conditions. Despite seasonal fluctuations, the lake exhibits moderate diversity and ecological stability, providing baseline data for long-term monitoring and sustainable management.