Quantitative study of plankton off Lawson's Bay, Waltair

Abstract

Observations on the hydrographical and planktological conditions of the surface waters at a fixed station located at the 10 fathom line in the Lawson's Bay, Waltair, have been made for the year 1956. The influence of the prevailing currents on the hydrographical conditions in the inshore waters of the Bay of Bengal is discussed. A north to south succession of the periods of low salinity and high silicate content at three stations Waltair, Madras and Mandapam on the east coast of India has been observed during the southerly current period, July to December. A similar succession of the high salinity values in a south to north direction during the northerly current period, January to June, has also been observed at Madras and Waltair. Quantitative plankton estimations have been made by counting, volume estimation, pigment extraction, total biomass and total organic matter for known volumes of water. There was general agreement between the data using the different methods. A major phytoplankton peak during March to April and a minor phytoplankton peak during October to November were observed. The diatom and dinoflagellate maxima coincided with each other. Pigment extraction was made with three different solvents and it was found that ethyl alcohol-benzene mixture was a better solvent than acetone and methyl alcohol. A general discussion is given on our observed data of plankton production in relation to the hydrographical conditions and inferences drawn in the light of similar investigations from Indian waters and elsewhere.