Zooplankton assemblages, water quality dynamics and molecular characterization of key crustacean taxa in human-impacted selected freshwater lakes of the Gangetic Plain, West Bengal, India

Freshwater lakes in the Gangetic plain of West Bengal encounter immense pressure due to high population density and intensive human activities, resulting in deterioration of water quality and aquatic biodiversity. Such information is essential for their sustainable management. The present study aimed to evaluate the physicochemical characteristics, crustacean zooplankton community, and molecular characterisation of key taxa from selected freshwater lakes over a period of one year. Physicochemical parameters were analysed using standard methods, crustacean zooplanktons were identified morphologically, and selected taxa were characterised based on partial mitochondrial COI gene sequences, followed by phylogenetic tree analysis. The Linear Mixed Model (LMM) suggested that regional climates primarily drive seasonal cycles in water characteristics, while lake morphometry, hydrology, and human inputs shape site-specific responses. Principal Component Analysis (PCA) revealed lake-specific environmental properties, with Bonhooghly showing nutrient enrichment, Joypur maintaining moderate water quality and Santragachi reflecting organic stress and reduced buffering capacity. The zooplankton community structure also varied in the three Lakes accordingly as reflected from the CCA result. Key crustacean copepod, ostracod and cladoceran zooplanktons comprised of Cyclops sp., Cypris subglobosa and Daphnia magna respectively. COI gene sequences revealed distinct genetic clustering of the investigated taxa relative to the available reference sequences, indicating genetic divergence and the need for further taxonomic and phylogeographic investigation. The study characterised the ecobiological features of the selected freshwater lakes from rural, suburban, and urban landscapes, aiding context-specific management strategies. The distinctiveness of the zooplankton groups suggests that Indian freshwater systems may harbour underexplored lineages, deserving further molecular and ecological study.