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

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Abstract
Changes in biochemical composition and 14C-bicarbonate assimilation into photosynthetic products were measured during a phytoplankton bloom in the southern Benguela upwelling region [South Africa]. In the decline phase, NO3 levels were < 1 mg at m-3 in the upper mixed layer chlorophyll a and protein concentrations decreased and a large proportion of assimilated C 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 C incorporated into protein at the 10 and 1% light levels indicated that the cells in the community were still viable under these conditions.