Dynamics of a Phaeocystis-dominated spring bloom in Belgian coastal waters. I. Phytoplanktonic activities and related parameters
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AbstractPhytoplanktonic activities were measured weekly during spring 1984 in Belgian coastal waters almost entirely dominated by Phaeocystis pouchetii colonies. Accurate methods were developed to measure photosynthesis and growth rates by colonial P. pouchetii cells, mucus secretion and excretion from colonies. Photosynthetic properties, although quite different for cellular photosynthesis and mucus secretion, were found to be independent of changes in environmental conditions. Maximal photosynthetic rates were respectively 0.09 and 0.16 h-1 for cells and mucus. Cellular specific growth rate, on the other hand, was inversely correlated to the level of ambient inorganic nitrogen. Extreme values for cell turnover rates were 0.12 and 0.38 d-'. A budget of metabohc activities of P. pouchetii colonies was established for the period of their bloom. The colonies photo-ass~milated 94 g C m-2 mo-l. From this, a maximum of 84 g C m-2 mo-1 was devoted to colonial biomass production 3nd 7.5 g C m-' mo-' was excreted from the colonies.