Variations in community structure of phytoplankton in relation to physicochemical properties of coastal waters, southeast coast of India

A comprehensive study on phytoplankton dynamics in the coastal waters of Kalpakkam showed a considerable increase (almost 3 fold) in phytoplankton species composition (185 species) as compared to the earlier findings (60 species). Despite such a massive change in floristic composition, 4-10 times reduction in total cell count was observed during the present study, which varied between 1.7 x 10 and 1.5 x 10 cells l. Another important feature of this study was the observation of Trichodesmium erythraeum bloom in the coastal waters. Concomitant with the bloom, a drastic fall in the number of phytoplankton species was noticed. The change in phytoplankton assemblages (density and species composition) during different seasons was significant and was found to be regulated by the change in water characteristics associated with monsoon. Diatoms dominated the phytoplankton assemblage followed by dinoflagellates. Asterionellopsis glacialis and Thalassionema nitzschioides were found to be dominant species among diatoms and dinoflagellates respectivaly, Prorocentrum micans and Protoperidinium sp. were the dominant forms. Salinity was found to be an important parameter influencing the species composition, standing stock and succession of phytoplankton at this location. Salinity apparently influenced the phytoplankton density positively. Nitrate was found to be the limiting factor for phytoplankton growth during late summer and pre-monsoon periods, whereas, the role of silicate and phosphate remained insignificant in this regard.