Seasonal Structuring of Zooplankton Communities as an Indicator of Ecosystem Health Along the Environmental Gradients in Ashtamudi Ramsar Wetland, India

Abstract

Ashtamudi Lake, a Ramsar-recognized tropical estuarine wetland of Kerala, exhibits pronounced spatial and seasonal variability driven by monsoonal hydrology and anthropogenic pressures. The present study evaluates the seasonal dynamics of zooplankton communities and their ecological responses to water quality across five distinct ecosites - Neendakara, Puthenthuruth, Asramam, Kidapram, and Cherikkadavu - during pre-monsoon, monsoon, and post-monsoon periods. Zooplankton and physicochemical parameters were analysed to elucidate species-environment relationships using an integrated statistical framework. A total of 45 zooplankton species belonging to Protozoa, Rotifera, Cladocera, and Copepoda were recorded, with overall abundance peaking during the monsoon season across all ecosites. Two-way ANOVA revealed significant effects of season, ecosite, and their interaction on zooplankton abundance, highlighting strong spatio-temporal regulation. Correlation analysis identified salinity, dissolved oxygen, nitrate, and phosphate as key environmental drivers. Community-level patterns derived from Non-metric Multidimensional Scaling demonstrated clear segregation along freshwater-estuarine gradients, while Canonical Correspondence Analysis confirmed distinct species-environment associations. Indicator Species Analysis further identified ecosite-specific zooplankton assemblages, emphasizing their diagnostic value. The results demonstrate that zooplankton communities in Ashtamudi Lake respond sensitively to hydrological forcing, nutrient dynamics, and localized anthropogenic stress, establishing a robust ecological baseline for long-term monitoring and sustainable management of tropical estuarine wetlands.