Studies made during April 1968 - April 1969, on the variations in the primary standing crop, in relation to oceanographic features such as upwelling, sinking and nutrient cycles, are presented.

Phytoplankton pigments have high values (ca. 150 mg/m2) during May-October and low values (ca. 20 mg/m2) during November-March. The poorest month is January, with a plant pigment content of less than 10 mg/m'.

With the onset of the southwest monsoon in May, the new cycle of production is triggered. The relatively high standing crop of phytoplankton during May-October is sustained by the nutrients brought up by upwelling and the increased run-off from the backwaters. By November sinking starts which continues till February, followed by stable conditions in March and April. During this period the nutrients get depleted and the standing crop also becomes very low, even though there is no dearth of sunlight.