Phytoplankton dynamics and pollution impacts in the Sundarbans estuarine ecosystem

Sundarbans belong exclusively to the largest mangrove ecosystem in the world. This work aims to track the spatiotemporal succession of phytoplankton relying upon microscopic study and hydrological parameters circumscribing five different locations of the Indian Sundarbans. Phytoplankton levels, the major contributors to aquatic productivity, should be kept under check to maintain a balanced ecosystem. Statistically validated environmental parameters and phytoplankton dissemination were thoroughly examined on a seasonal and spatial basis from April 2022 to February 2024. With regard to biomass, Bacillariophyceae exhibited prominence with maximum species richness (3.96), diversity (3.67) and assemblage observed during summer (4.7 × 103 ind/L). However, as winter commenced, the immense tourist load on 3 of our sampling stations, Gadkhali, Kumirmari and Dobanki, serving as the main tourist attraction spots, started facing pollution pressure attributable to garbage disposal, poor sanitation and littering from mechanized tourist vessels. This was further reflected in the phytoplankton community as a sudden surge in the Dinoflagellate population owing to blooms of Ceratium sp. (15.6 × 103 ind/L) was observed, indicating pollution pressure in the waterbodies, further validated by the increased heavy metal concentration (Lead, Cadmium and Chromium) and COD levels (47.34 ± 3.09 mg/l) during this season. A multidimensional scaling map further validated the similarity trend across these stations, pointing towards the implications of uncontrolled tourism as the probable cause. Therefore, it is essential to impose ecotourism practices keeping in mind the tourist carrying capacity of the ecosystem.