Phytoplankton Community Response to Environmental Changes in Mahanadi Estuary and Its Adjoining Coastal Waters of Bay of Bengal: a Multivariate and Remote Sensing Approach

The present study investigates seasonal variability of physicochemical parameters and phytoplankton community structure, abundance, and chlorophyll a (Chl a) during 2007–2009 in the Mahanadi estuary, Bay of Bengal (BoB). Seasonal variations of phytoplankton community depended upon the change in hydrographic conditions and nutrient concentrations of the estuarine ecosystem. The changing scenario of phytoplankton community structure in relation to the various physicochemical properties of the ambient water was influenced by the monsoon and post-monsoon cycle. Discernible variation was observed in phytoplankton species composition, population density, and Chl a concentration between the pre-monsoon (April), monsoon (July), and post-monsoon (October). The mean population density of phytoplankton varied from monsoon (29,276 cells l−1) to pre-monsoon (43,290 cells l−1) period. Multivariate analyses showed that diatom was the most dominant (57.63%) followed by dinoflagellates (33.05%) compared with other communities in the study area. The green and blue-green algae were dominant during monsoon, while coccolithophores and silicoflagellates were the major during pre-monsoon. The Chl a concentration leads to the population density and varied between 0.87 and 1.18 mg m−3 from pre-monsoon to post-monsoon. Salinity and suspended solids (SS) played a major role in the spatial and seasonal distribution of phytoplankton composition and showed a positive correlation (p < 0.01) between nitrogenous nutrients (NO3 and NO2) with phytoplankton density and Chl a, suggesting that nitrogenous nutrients have profound influence on the phytoplankton growth. The in situ Chl a data used for validation of composite satellite MODIS data and result found that both data showed a similar trend of distribution in the region. The Chl a concentration was significantly higher in the pre-monsoon period.