Studies on the bloom-forming species of phytoplankton in the Vellar estuary, southeast coast of India

Fortnightly phytoplankton samplings have been made in Vellar estuary, during the relatively stable hydrographical period of February to July 1997. The bloom-forming consisted of different species of diatoms (II), dinoflagellate (I) and blue-green (1). The forms like Coscinodiscus centralis, Planktoniella sol, Bellerochea malleus, Odontella sinensis, Thalassiothrix frauenfeldii, Thalassionena nitzschioides, Ceratium furca, Trichodesmium erythraeum, etc., were found to be dominant. The surface water temperature, salinity ,pH and dissolved oxygen remained fairly stable during the entire period of observation. Generally, then nutrients concentration showed lower values when the phytoplankton density was at its peak. The dominant index of phytoplankton ranged from 41.80% to 100%. The observed very high population density of 1,99,600 cells l(-1) of phytoplankton could be due to the higher levels of salinity (35%o) and dissolved oxygen (7.15 ml l(-1)).