Influence of Water quality on the biodiversity of phytoplankton in Dhamra River Estuary of Odisha Coast, Bay of Bengal

Dhamra estuarine ecosystem is a hotspot of rich biological diversity which supports a patch of mangrove along with unique flora and fauna. In this study, the diversity of phytoplankton population and other factors that control their growth and biodiversity were investigated. The samples were collected monthly from Dhamra estuary of Bay of Bengal at 6 different stations (grouped under three regions) from March -2008 to February -2009. A total of 41 genera of phytoplankton species belonging to 4 classes of algae were identified. The maximum value of 9.3 X 10 cells l was recorded in post monsoon season. Phytoplankton of Bacillariophyceae, appearing throughout the year, and represent majority of population (75-94%) at all the sampling stations, followed by Dinophyceae (3-14%), Cyanophyceae (3-8%) and Chlorophyceae (0-4%) classes. The Shannonweavers diversity index (H) remains between 0.22 and 2.49. Based on the correlation coefficient data, phytoplankton shows positive relationship with DO, salinity, nutrients and negative relationship with temperature and turbidity. Present study shows that the occurrence and diversity of these primary producers do not subscribe to a single dimensional phenomenon of a single factor, rather than, a consequence of a series of supported factors which will help to maintain and balance such type of fragile ecosystem. @JASEM Estuaries are characterized by the gradient of salinity in a semi enclosed coastal system, flourishing a group of organisms uniquely capable of using the salinity gradient to a competitive advantage. Phytoplanktons represent the base of pelagic food webs in estuarine ecosystem and play a major role in the global cycling of carbon, nitrogen, phosphorus and other elements and the regulation of earth’s climate. The biomass distribution and species composition of phytoplankton have important effects on carbon fixation rates and on transfer of energy in food webs. Studies of the abundance, distribution and composition of phytoplankton communities are, therefore, a fundamental contribution to our understanding of the structure and function of estuarine ecosystems. Phytoplankton communities are multispecies communities, which are highly multifaceted in terms of their diversity and dynamics. Successional shifts in phytoplankton community structure are mainly due to changes in environmental variables such as nutrients and other physicochemical variables which influence the distribution and abundance of plankton communities in estuaries (Cleorn, 1987; Ferreira et al., 2005; Madhu et al., 2007). Estuarine regions are important sinks for several elements. In this study we tried to identify and asses the trend of phytoplankton species diversity at Dhamra Estuarine region with the water physico – chemical parameters. Dhamra river is the union of river Brahmani and Baitarani, the two largest rivers of Orissa, situated at the Bhadrakh district, just north of the boundary of Bhitarkanika wild life sanctuary, famous for its estuarine crocodiles and approximately 10 km from the Gahirmatha marine sanctuary, which is the world’s most important nesting beach for Olive Ridley sea turtles on the Orissa coast of Bay of Bengal. Although, a number of studies have been carried out on the ecological conditions of estuarine region, as Bay of Bengal is considered as a low productive zone (Madhupratap, et al., 2003), very limited work has been done in the east coast of Orissa. Moreover, not as much of information on phytoplankton species composition and diversity is available in this particular estuarine region. MATERIALS AND METHODS Sampling of surface water was carried out throughout the year (March-2008 to February-2009) on a monthly basis at Dhamra River Estuarine region. A total of 6 stations ,where station-1 and 2 covers the lower estuarine region (marine region, depth-63 ft), station-3 and station-4 covers the river mouth region having depth of 27ft and 26ft, respectively and station-5 (26ft) and station-6 (26ft) were the riverine region or fluvial region dominated by freshwater but subjected to tidal action. Water samples for the measurement of salinity, turbidity and nutrient parameters were collected in Polypropylene bottles and for DO and BOD measurement, water samples were collected in DO bottles and analysed by Winkler method. The temperature and salinity was measured in situ using sensor based Multi WTW 340i/set. Salinity was again cross-checked by silver nitrate titration (Oxner, 1920). Turbidity was measured by Nephlometric method using HACH 2100P Turbidimeter. Basic nutrient parameters (nitrite, nitrate, ammonia and