The Relationship between N/P/Si Stoichiometry and Phytoplankton Blooms in the Surf Zone Coastal Waters, Southwestern Bay of Bengal

Phytoplankton blooms represent a sudden increase in microalgae biomass, generally last for a week or so. Typically, they consist of one particular species dominating the plankton in the surface water, characterized by colorations of water due to high concentrations of photosynthetic pigments in the microalgae. Hence, the present study explores the variability of nutrient ratios that alters the phytoplankton community structure, competition, and succession between algal species for the coastal water of the western Bay of Bengal. An intense bloom of four phytoplankton species, i.e., the diatom (Asterionellopsis glacialis), followed by the green alga (Chlorella salina), the cyanobacteria (Trichodesmium thiebautii), and the diatom (Chaetoceros diadema), was encountered within the surf zone of Chennai coast on the 13^th,15^th and 19^th of January 2015, and the 17^th of February 2016, respectively. Chlorophyll-a (Chl-a) concentration was increased by 10-fold during the bloom period compared to the non-bloom period. A higher Si:P ratio favored the bloom of A. glacialis and C. diadema and during lower ratio resulted in the bloom of C. salina. T. thiebautii bloom forms at a higher concentration of N:P ratio and a lower ratio resulted in C. salina bloom. Along with the nutrient ratio, the concentration of dissolved inorganic nitrogen (DIN) and surface water temperature also favored the bloom conditions within the surf zones. Multivariate analysis showed that SiO4 and Si:P ratio were important environmental factors that induced the growth of A. glacialis, and C. diadema. The favorable temperature and nutrient ratios (Si:P and N:P) along this coast during the post-northeast monsoon period trigger the proliferation of algal blooms. The present study reported the first of its kind on phytoplankton succession along the east coast of India.