Present study consists of phytoplankton community of Gopalpur creek in pre-monsoon, monsoon and post-monsoon season There was a Significant seasonal variation in water temperature (p < 0.01). Salinity and pH varied significantly (p < 0.05) among the stations. Chlorophyll a and phytoplankton density found to vary significantly (p < 0.01) among seasons rather than the stations. A total of 99 phytoplankton species were identified. Diatoms formed 77, dinoflagellates 14, green algae five, blue green algae two and cocolithophore one species. Phytoplankton species composition was found dissimilar in the three seasons. In pre-monsoon Noctiluca scintillans, Thalassiothrix longissima, Odontella sinensis, Thalassionema nitzschioides, Coscinodiscus gigas, Rhizosolenia alata formed the dominant species. In monsoon, Rhizosolenia alata, Pleurosigma elongatum, Melosira sulcata, Amphora coastatum, Rhizosolenia setigera dominated the phytoplankton population. In post-monsoon Odontella sinensis, Rhizosolenia setigera, Coscinodiscus gigas, Thalassiothrix longissima, Noctiluca scintillans, Oscillatoria spp. dominated. Univariate diversity indices showed maximum diversity during post-monsoon. Pielou's evenness (J') and Simpson's dominance have shown little variation among the seasons.
