Seasonal and tidal variations of phytoplankton in the gradient zone of Vellar Estuary

Abstract

The phytoplankton variations in relation to other environmental parameters were studied from January 1977 to December 1978 in the gradient zone of the Vellar Estuary. Among 155 species of phytoplankton, diatoms (102 spp) and dinoflagellates (35 spp) were the dominant groups and occurred throughout the year except in some collections during the monsoon season. Phytoplankton population density varied from 22 cells/l to 138 x 104 cells/l and the density was high during summer and premonsoon season and low during monsoon season. Although the density was found to be higher in day collections than night collections, it was statistically not significant. Wide fluctuations in species diversity (0.3 to 4.3 bits/individual), species richness (0.16 to 4.0) and evenness (0.1 to 0.98) were observed. Species diversity at high tide was higher than at low tide. Salinity was found to play a major role in determining the species composition, succession and density of phytoplankton