Spatial variation in phytoplankton dynamics in the Belgian coastal zone of the North Sea studied by microscopy, HPLC-CHEMTAX and underway fluorescence recordings

Abstract

Spatial variation in the succession of phytoplankton in the Belgian Coastal Zone (BCZ) was investigated by monitoring phytoplankton biomass and community composition using microscopical cell counts, HPLC pigment analyses and in vivo fluorescence recordings. Monthly monitoring of phytoplankton community composition at five stations revealed a succession of three distinct diatom communities. The succession of these three communities was the same at each site, but the succession from the winter-spring to the summer community occurred one month earlier and the succession from the summer to the autumn community one month later at the SW than at the NE stations of the BCZ. Monthly monitoring of chlorophyll a at ten fixed sites and inspection of in vivo fluorescence recordings during various cruises of RV ‘Zeeleeuw’ indicated that the spring bloom started about one month earlier in the SW part of the BCZ than in the NE part. The spatial difference in the onset of the spring bloom was ascribed to the higher water column turbidity at the NE coast compared to the SW coast. Although a Phaeocystis bloom occurred at all monitoring stations, a clear spatial variation in the magnitude of such blooms was observed, with more intense blooms at the NE coast than at the SW coast. A close relation was observed between the intensity of the Phaeocystis bloom and the availability of inorganic nutrients (N and P) before the onset of the bloom. Comparison of microscopical cell counts and CHEMTAX analysis of accessory pigment data indicated that HPLC analysis may be a useful tool for monitoring Phaeocystis in the North Sea. The presence of chlorophyll c 3 containing diatoms, however, probably resulted in the detection of small quantities of Phaeocystis by HPLC-CHEMTAX analysis when microscopical analyses showed that the species was absent.