DISTRIBUTION AND ABUNDANCE OF PHYTOPLANKTON IN VEMBANAD ESTUARY, A RAMSAR SITE ON SOUTH WEST COAST INDIA

The phytoplankton abundance and distribution from the Vembanad estuary, south west coast of India was studied for a period of two years from March, 2011 to February, 2013. A total of 73 genera of phytoplankton were recorded and Bacillariophyceae formed the dominant group in all seasons of the study. The constant addition of nutrients particularly, nitrate and phosphate based fertilizers used in the Kuttanad paddy fields enhanced the phytoplankton production in the estuary. During 2011-2012 and 2012-2013 period, phytoplankton biomass varied from 2 to 46 ml/m3 (av. 11.09 ml/m3) and 1 to 26 ml/m3 (av. 5.78 ml/m3) respectively. Phytoplankton biomass, distribution and species composition showed variations in contrast to the prevailing water temperature, light intensity (Secchi disc visibility), nutrient availability, grazing pressure, tide and water movements, and seasonal pattern and even with time of day. The salinity regime of the water body also influenced the phytoplankton distribution in the study locations. Phytoplankton production showed a higher value in the northern as compared to the southern zone. Thus, the mesohaline condition prevailing in the northern zone of the estuary supported higher abundance and diversity of phytoplankton species which in turn contributed to higher production rate.