Phytoplankton of the Indian Ocean: some ecological problems

Abstract

Investigations on the ecology of the phytoplankton of the Indian Ocean are scanty and confined to the inshore waters. The results of the international Indian ocean expedition so far published give a cursory picture of the phytoplankton of the oceanic waters. In thepresent account some preliminary results of continuous ecological investigations of the shelf and oceanic areas on the west coast of India between 6°-16°N and 72"-77°E, based on the collections of R. V. VARUNA are deah with and compared with the earlier observations. The shelf and oceanic waters on the west coast of India presents the same trend in the fluctuation of the standing crop of phytoplankton. During the southwest monsoon months(April to October), the displacement volume of the standing crop is high, the peak occurring in July; from November onwards, the values diminish reaching the minimum in February. The bulk of the crop is Constituted by the Diatomaceae. Available data indicate that the waters of the west coast of the Indian Peninsula are more fertile than those of the east coast mainly due to the extensive upwelling and other favourable factors conducive to plankton growth; a few species always contribute to the bulk of the crop though rnany occur, while this cannot be stated for the east coast where at a given time no single species is in domination could be noted. A similar pattern is reflected in the constituents offish landings-while a few contribute to the bulk of the catches on the west coast, the bulk on the east coast is always made up by many species. Some of the probable ecologicalfactors contributing to the pattern of production of the phytoplankton are also discussed.