The spring bloom of phaeocystis pouchetii (haptophyceae) in Dutch coastal waters

A Phaeocystis pouchetii (Harlot) Langerh. bloom, which contained up to 22×106 cells ·dm−3, occurred in the spring of 1984 along the Dutch coast of the North Sea. The largest cell numbers of P. pouchetii were observed near the coast, with cell numbers decreasing towards the open sea. In contrast to a shark peak in the cell numbers along the coast in May, P. pouchetii cell numbers in the open sea slowly increased towards June.During a preceding bloom of diatom, P. pouchetii was already present from an early stage onwards while at the end of the P. pouchetii bloom a high percentage of the cells was observed as microflagellates.The distribution of dissolved nutrients (Si, N, P) showed a typical pattern with highest values near the coast, apparently due to the Rhine outflow, and a gradual decrease towards the open water. This distribution pattern coincided with particular stages of the P. pouchetii bloom. Whereas growth of the P. pouchetii population may be due to increasing temperature and irradiance, its decline is probably caused by phosphate limitation.Total primary production measured at one station and based on short term 14C incubation experiments was 121 gC·m−2 for the period 17 March to 20 May with a daily rate of production of up to 4.8 gC·m−2. The mean proportion of extracellular carbon release based on 4 h incubation periods was 7.5