On the possible causes of the seasonal phytoplankton blooms along the southwest coast of India

Abstract

Data collected off the southwest coast of India at the onset of the 1987 southwest monsoon season suggest that the commonly observed high concentrations of chlorophyll and rates of photosynthesis of the season may not be due to greatly enhanced chlorophyll-specific (normalized) photosynthetic rates of the bulk phytoplankton. Instead it is proposed that the seasonally increased nutrient supply primarily increases the growth rate of the otherwise more diffusion-limited large-celled species, which then can materially increase in numbers, since they are poorly controlled by grazers. If so, the principal role of the high nutrient concentrations would be to permit the build-up of a large algal biomass and pigment concentrations that, coupled with moderate normalized photosynthetic rates, yield the observed high production rates per m(3) and m(2) of the upwelling season.