The species composition, abundance and diversity of phytoplankton including diatoms, cyanobacteria, dinoflagellates and planktonic green algae, were studied in the Netravathi- Gurupura estuarine waters near Mangalore, west coast of India. Water samples were collected from three different sampling sites during three different seasons over a period of one year from June 2010 to May 2011 and physico-chemical parameters of water were recorded. A total of 80 species of phytoplankton were identified out of which 54 were diatoms (67.5%), 15 were cyanobacteria (18.75 %), 6 were planktonic green algae (7.5%) and 5 belonged to dinoflagellates (6.25 %). The density of total phytoplankton ranged between 16.94x10³ cells/l-1 and 28.64 x10³cells/l-1. The maximum density of phytoplankton was observed during post monsoon season coinciding with most stable hydrological conditions. Phytoplankton species diversity was also detected in different sampling stations. Shannon- Wiener’s (H’) diversity index of phytoplankton population ranged from 1.52 to 2.69. In addition, the species richness index (d’) ranged between 0.42 and 1.98 and evenness index between 0.67 and 0.95 (J’). The diversity indices show the instability of the system particularly during monsoon because of dominance of single species. The diatoms were found to be dominant in these waters.

Phytoplankton, Nethravathi-Gurupura estuary, diversity, south west coast of India.