Phytoplankton community structure of the Gangetic (Hooghly-Matla) estuary: Status and ecological implications in relation to eco-climatic variability

This study consolidated our understanding on community structure of phytoplankton of the Gangetic estuary (Hooghly-Matla) based on both bibliographic sources and field studies. A total of 378 species of phytoplankton taxa belonging to 196 genera and 109 families were reported from the Hooghly-Matla estuarine system which is among the major biodiversity hotspots of the world and plays a pivotal role as nursery ground for fish and shell species. Being an estuarine system its working as a sink for abatement of the pollutants and plays an important role in mitigating flood and other catastrophic changes mediated due to climatic invariability. About 97% of these phytoplankton taxa (365 species) are distributed across four major groups; the diatoms constitute 52% of the phytoplankton diversity with 195 species, followed by the green algae (82 species), blue-green algae (59 species) and dinoflagellates (29 species). Moreover, there are four minor groups that constitute the remaining 3% of phytoplankton taxa with 13 species. Our survey on the phytoplankton communities of the tidal freshwater zone recorded 91 species of phytoplankton, with dominance of green algae (41 species) followed by diatoms (34 species). Our own studies also revealed ecological indicator groups, with diatoms being dominant in open estuarine waters, whereas the estuarine wetlands were mainly inhabited by blue-green algae. A literature review revealed indicator plankton species for issues of global climate change and sea level rise in India and its neighbouring countries. Due to immense ecological variability, a shift in phytoplankton community structure was revealed in available literature. This article illustrates status of phytoplankton communities and their population dynamics along the entire estuarine system, providing a sound base for assessing impact studies and solving transboundary issues between India and adjoining countries.