Proliferation of dinoflagellates in Kochi estuary, Kerala.

Phytoplankton community structure and dynamics of Kochi estuary (bar mouth) have been studied seasonally. Three seasonal samplings namely pre-monsoon, monsoon and post-monsoon were made, and a wide variation was observed in phytoplankton community with respect to nutrients and other physicochemical parameters. Contrary to other seasons, dinoflagellate cell density increased during pre-monsoon season though species diversity was less pronounced (D > 0.15). Peridinium oceanicum was the dominant dinoflagellate during pre-monsoon season. Significant fluctuation in three principal nutrients namely total nitrogen, total phosphorous and silicate were observed during pre-monsoon (TP < 1.8 micromol l(-1), TN > 40 micromol l(-1) and SiO4 < 20 micromol l(-1)) season as compared to monsoon season (TP > 3.20 micromol l(-1), TN < 20 micromol l(-1) and SiO4 > 27 micromol l(-1)). Salinity values were also found to be high during pre-monsoon ( > 25 psu). Study suggests that variation in salinity and nutrient concentration during transition of seasons could result in succession of species, thereby causing change in phytoplankton community structure. High salinity and nitrogen values along with low values of silicate and phosphorous resulted in proliferation of dinoflagellates during pre-monsoon season.