Dynamics of the decline of a phytoplankton bloom after an upwelling event

Abstract

[Changes in biochemical composition and ¹⁴C-bicarbonate assimilation into photosynthetic products were measured during a phytoplankton bloom in the southern Benguela upwelling region. In the decline phase nitrate levels were < 1 mg at m⁻³ in the upper mixed layer, chlorophyll a and protein concentrations decreased and a large proportion of assimilated carbon was detected in the ethanol-soluble fraction at the 50 % light level. As the cells sank out of the mixed layer, chlorophyll a and protein concentrations increased in the stable and bottom layers. Although the photosynthetic rate was slower in these layers, increased protein/glucan ratios and the large proportion of carbon incorporated into protein at the 10 and 1 % light levels indicated that the cells in the community were still viable under these conditions.]