|Phaeocystis spring bloom in the continental coastal zone of the North Sea|
Rousseau, V.; Lancelot, C. (1989). Phaeocystis spring bloom in the continental coastal zone of the North Sea, in: Pichot, G. (Ed.) Progress in Belgian Oceanographic Research 1989: proceedings of the North Sea Symposium held in Ghent, 14 February 1989. pp. 225-245
In: Pichot, G. (Ed.) (1989). Progress in Belgian Oceanographic Research 1989: proceedings of the North Sea Symposium held in Ghent, 14 February 1989. Management Unit of the Mathematical Model of the North Sea and Scheldt Estuary: Brussel. 451 pp., more
Phaeocystis blooms and correlated hydrological variables were intensively monitored in the continental North Sea -from France to Germany -during the year 1988, in the frame of a joint E.E.C. research project on the dynamics of Phaeocystis blooms in nutrients enriched coastal zones. It is shown that the peculiar climatic conditions prevailing during winter 1988, resulted in unusual phytoplankton growing conditions characterized by a 2°C higher ambiant temperature, a higher turbidity and higher nutrients concentrations. The increase of these latter was particularly important in the Northern part of the studied area where nitrogen and silica concentrations as high as 90 and 50 umole.l-1 were reached, due to the cumulative effect of river inputs. In response to this nutrients enrichment, phytoplankton blooms developed in the whole area since mid April and reached maximum values at ambiant temperature of 10°C. Maximum Chla concentrations of 5 ugl-1 were recorded in the oligotrophic waters of the Western Channel and of 25-35 ug.l-1 in the eutrophicated Belgian, Dutch and German coastal waters. .analysis clearly showed that Phaeocystis successfully developed at time where depleted by diatoms and reached Chla biomass as high as 35 ug.l-1 in the Belgian coastal zone, representing 80 % of the total spring phytoplankton biomass. Contrary to previous years, the two taxonomic groups -diatoms and Phaeocystis -overlapped during a few days up to the silica depletion. Regression analysis of nitrogen and phosphorus concentrations indicated that nitrogen is the most likely nutrient limiting Phaeocystis growth in the French coastal zone and phosphate in the Dutch coastal zone. Light availability, on the other hand, was the factor controlling Phaeocystis efflorescence in the Belgian coastal zone.