Seasonal variations of phytoplankton in Mahanadi estuary, east coast of India

184-190Seasonal variations of phytoplankton and chlorophyll-a along with its environmental variations including nutrients were studied from June-2004 to March-2007. Samples were collected in three different seasons pre-monsoon (May-June), post-monsoon (October-November) and summer (February-March) from the Mahanadi estuary. Seventy seven species of phytoplankton were encountered during the study period of which, diatoms (Bacillariophyceae) was the dominant group followed by dinoflagellates (Dinophyceae) and cyanobacteria (Cyanophyceae). Higher phytoplankton counts and chlorophyll-a concentrations were recorded in post-monsoon season. Nutrient concentration was also very high in the above season as compared to other two seasons. Cyanobacteria population was more during post-monsoon season. Positive correlations of phytoplankton, with chlorophyll-a and dissolved oxygen were recorded in all three sampling seasons. Positive correlation of phytoplankton population with Chl-a, DO, NO2-N, NH4-N indicated that the phytoplankton population in the estuary is controlled by above nutrients. Diatoms are dependent on NO2-N and NH4-N, dinoflagellates depend on NO2-N and SiO4. Cyanobacteria in the estuary depend on NO2-N, NH4 and PO4