CHEMICAL AND PHYSIOLOGICAL-CHANGES OF PHYTOPLANKTON DURING THE SPRING BLOOM, DOMINATED BY PHAEOCYSTIS-POUCHETII (HAPTOPHYCEAE) - OBSERVATIONS IN DUTCH COASTAL WATERS OF THE NORTH-SEA

During the spring bloom of phytoplankton in Dutch coastal waters of the North Sea the flux of 14C-labelled products into pools of protein, polysaccharides, small metabolic intermediates and lipids was studied. The molecular size distribution of extracellular products, amounting to 28% of the particulate production, was determined by gel filtration. Concentrations of protein and carbohydrates were determined in the same phytoplankton samples. At an early stage of the bloom protein synthesis and protein concentration dominated over carbohydrate synthesis and carbohydrate concentration, but after the peak of the blood carbohydrates were the predominant photosynthetic endproduct. These observations have been compared to similar observations on unialgal cultures of Phaeocystis pouchetii. The influence of phosphate depletion of the extracellular release of organic compounds and the impact of the colonial growth form of Phaeocystis pouchetii on the distribution of intra- and extracellular labelled compounds are also discussed.