Influence of environmental variables on phytoplankton floristic pattern along the shallow coasts of southwest Bay of Bengal

Multivariate statistical methods are used to study the spatial and temporal variations of physico-chemical parameters and phytoplankton floristics of the southwest coast of Bay of Bengal. Over 94 species of phytoplankton represented by 77 species of diatoms, 11 species of dinoflagellates and 6 species of blue-green algae were recorded. Higher phytoplankon species diversity was found in premonsoon when salinity and nitrate concentrations were low and reactive silicate and inorganic phosphates were moderate, while species diversity was low during summer with when increased sea surface temperature, salinity and low nutrients availability. During summer season Coscinodiscus centralis, Diatoma vulgare and Rhizosolenia alata were dominant, especially Coscinodiscus sp. distributed in all stations whereas Skeletonema costatum, Biddulphia sinensis and Ditylum brightwelli were abundant in the premonsoon season. From principal component analysis and multiple regression analysis, it is evident that variables like sea surface temperature and light extinction coefficient are the most important factors influencing the seasonal pattern of phytoplankton population, although nutrients like nitrate, inorganic phosphate and silicate have also important contributors in deriving phytoplankton population density of this part of the Bay of Bengal.