A study was conducted to evaluate the phytoplankton community structure and its relationship with selected physicochemical variables in the inshore waters of Tuticorin during January to December 2008. Water and plankton samples from the surface waters at two depths (5m and 10m) were collected on board the research vessel Cadalmin-IV. Standard methods were followed for phytoplankton identification, enumeration and estimation of physicochemical variables. The present study recorded 69 species of phytoplankton with 85.5% dominance of diatoms followed by 14.5% of dinoflagellates. The overall density of phytoplankton was comparatively higher at 10 m with a mean of 2.14x104±0.4x104cells L-1 and 3.37x104±0.9x104cells L-1 at 5 m and 10 m depth respectively. The analysis indicated that 10 m depth, especially during the monsoon season, is rich in diversity of algal species than at the same depth during post-monsoon. It is confirmed that the population density of phytoplankton is more influenced by seasonal fluctuation of the physicochemical variables especially due to the effect of northeast monsoon in the inshore waters of Tuticorin.

Phytoplankton, physicochemical variables, inshore waters, northeast monsoon