The Vembanad Lake, a significant Ramsar wetland, faces ecological challenges due to dynamic physicochemical conditions and anthropogenic nutrient loading. This study investigated the influence of key environmental variables such as Salinity, Nitrate and Phosphate on the spatial distribution and diversity of phytoplankton across three distinct micro-habitats namely Kainakari Vattakkayal, Meenappally Kayal, and Venattukadu Kayal. Water and plankton samples were collected and community structure was analysed using diversity indices such as Shannon-Wiener H', Species Richness (S), and Pielou's Evenness (J') as well as Canonical Correspondence Analysis (CCA). The results revealed a clear environmental gradient decreasing from Kainakari Vattakkayal to Venattukadu Kayal, which directly mirrored the phytoplankton diversity. Kainakari Vattakkayal is the area with the highest salinity and nutrient concentrations, supported the highest diversity and richness, exhibiting dominance by Chlorophyceae and Cyanophyceae, taxa often associated with nutrient enrichment. Conversely, the intermediate physicochemical regime at Meenappally Kayal facilitated the highest total density of phytoplankton and was strongly dominated by Bacillariophyceae (diatoms). The CCA confirmed that Salinity, Nitrate, and Phosphate were the dominant ecological drivers, rigorously structuring the phytoplankton communities across the sites. These findings underscore the critical role of the physicochemical environment in shaping the primary producers of the Vembanad Lake, highlighting the need for targeted management strategies to mitigate the impacts of spatial variations in hydrography and nutrient inputs.

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