Salinity variations drive the phytoplankton dynamics in the Gangetic estuary: insights from the modelling approach for species responses and pollution indicators along the longitudinal estuarine gradient

Spatial and temporal variation in phytoplankton assemblage and their species responses with varying salinity regimes were investigated in the Hooghly Matlah estuary, India during two annual period. The exhaustive survey in the ten sampling stations recorded 132 species of phytoplankton belonging to 95 genera. The study revealed 12 taxonomic algal groups with the dominance of class Bacillariophyceae (43 species). Indicator species analysis revealed the dominance of Aulacoseira granulata, Scenedesmus quadricauda, Eudorina sp. and Protococcus sp. in the tidal freshwater zone while a higher proportion of Pleurosigma sp., Synedra sp. and Coscinodiscus sp. were observed in the intermediate zone. The middle and lower estuary were dominant with Cyclotella sp. and Closterium sp. in upper Sundarbans and Entomoneis sp. and Chaetoceros sp. in lower Sundarbans. Species response curve using GAM modelling was performed to identify the taxa that had their population maximum in various saline zones of the estuary.