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Phytoplankton, the primary producers of all aquatic systems, form the base of the marine food web. Any change in the environmental settings of the given ecosystem will affect the phytoplankton community structure of the region. In the present work, water sampling was carried out from the poorly explored polar region, beneath the sea ice during the melting phase of land-fast ice near Indian Antarctic Research Station Bharati in Prydz Bay, East Antarctica. The water samples were analyzed for phytoplankton species diversity, nutrients, temperature, salinity, and Chlorophyll a (Chl a). Our observations indicate marked variations in phytoplankton biomass and community. A shift from diatom (Thalassiosira sp., Fragilariopsis sp.) to dinoflagellate (Protoperidinium sp.) community, along with the emergence of grazers was seen by the end of the observation period. The background environmental conditions also showed marked variations, as the concentration of nitrate at 0m depth reduced from 31.8 μM at Obs-1 to a non-detectable limit at Obs-3. Furthermore, at 0m depth, temperature increased from −1.32 °C at Obs-1 to −0.38 °C at Obs-3 while salinity decreased from 34.11 at Obs-1 to 33.68 at Obs-3, thus indicating the melting phase of sea ice from Obs-1 to Obs-3. These observations showed vertical stratification resulting from the basal melting of land-fast sea ice resulted in better availability of light, phytoplankton community change due to nutrient availability/utilization/limitation, followed by the presence of grazer community. This preliminary understanding will serve as a baseline dataset to design the targeted sampling/experiments in the future from the land-fast ice ecosystem. [ABSTRACT FROM AUTHOR]