Elucidating the role of environmental conditions and nutrients in shaping phytoplankton structures in the Cox’s Bazar coast, Bay of Bengal

Phytoplankton communities play a crucial role in marine ecosystems, serving as primary producers and indicators of environmental changes. This study investigates the spatial and temporal variations in phytoplankton structure along the Cox’s Bazar coast of the Bay of Bengal, Bangladesh, in relation to environmental parameters (Temperature, Salinity, pH, DO, Water Current) and nutrient dynamics (NO₂-N, NO₃-N, NH₄-N, PO₄-P, SiO₄-Si). Water samples from 12 stations across Bakhkhali, Moheshkhali, Nunier Chara, and Sonadia Island were analyzed to assess phytoplankton diversity and abundance. A total of 34 phytoplankton genera from four major classes—Bacillariophyceae, Dinophyceae, Cyanophyceae, and Chlorophyceae—were identified, with Bacillariophyceae being the most dominant. Canonical Correspondence Analysis (CCA) revealed that temperature and salinity were the primary drivers of phytoplankton distribution, while ammonium, phosphate, and dissolved oxygen played secondary roles. Seasonal trends indicated that Chlorophyceae preferred higher temperatures and dynamic water conditions, whereas Bacillariophyceae thrived in low salinity environments. The dominance of Thalassiosira, Skeletonema, and Chaetoceros at Moheshkhali suggested high primary productivity, while Pseudo-nitzschia abundance at Nunier Chara raised concerns about potential harmful algal blooms. The findings underscore the ecological significance of phytoplankton in coastal waters and provide valuable insights for sustainable fisheries management and marine ecosystem conservation.