Abstract:
Estuaries are among the most productive marine ecosystems in the world (Gameiro et al., 2004) and they act as transitional zones between land and sea and receive constant nutrient supply from rivers and land based discharges. In order to examine the phytoplankton community composition in the Godavari estuary, physicochemical and biological samples were collected during three discharge periods (June 2024 to January 2025) in the Godavari estuary. Even though the concentration of nutrients were high during peak discharge period, the phytoplankton content was less due to high suspended matter (>150 mg/l) and less light penetration. In contrast during moderate discharge period and when there was no discharge the phytoplankton biomass was high (>5µg/l) with the composition of Coscinodiscus sp, Chaetoceros, Thalassiosera, Thallasiotrix, Ceratium etc. This suggests that decrease in suspended load, decrease in river discharge and increase in stability of water column are the major controlling factors determining phytoplankton growth. Overall Phytoplankton cells showed a wide range from 1,000 to 45,962 cells/l (ave.7,799 cells/l). Diatoms were the major dominant group. During peak discharge period phytoplankton abundance was contributed by diatoms with a range of 1,000 to 3,896 cells/l (ave. 7,135 cells/l), whereas during moderate and no discharge periods the numbers were more, 3,000 to 45,962 cells/l (ave. 11,738 cells/l) and 1,000 to 41,609 cells/l (ave. 7,527 cells/l) respectively. The variations were similar with biomass (Chl-a) during the three discharge periods. The variations of nutrients and salinity suggest that decrease in salinity and increase in nutrients enhanced phytoplankton growth in the estuary. These results suggest that changes in the freshwater discharge and salinity brought a significant variation in phytoplankton composition in the Godavari estuary.