Climate change and harmful algal blooms in the North Sea

The projected effect of climate change for the year 2100 in the coastal zone of The Netherlands, a 4 C temperature rise and increased salinity stratification. on the growth rates of six harmful and two non-harmful phytoplankton species was investigated in batch laboratory cultures. Stratification can split the mixed water column (18 degreesC, 150 W h m(-2) per day) into a bottom (18 degreesC, 10 W h m(-2) per day) and surface layer (22 degreesC, 600 W h m(-2) per day); these three conditions (the present scenario) were compared to a 2100 scenario in which temperatures were increased by 4 degreesC. The growth rates of the two non-harmful species, the diatom Skeletonenta costatum and the cryptophyte Rbodomonas sp. did not significantly change from present-mixed to 2100-surface conditions. Two harmful species, the prymnesiophyte Phaeocystis globosa and the diatom Pseudo-nitzschia multiseries, died rapidly at the 2100-surface conditions. On the other hand, two dinoflagellates (Prorocentrum micans and Prorocentrum minimum) and two raphidophytes (Fibrocapsa japonica and Chattonella antiqua) doubled their growth rates at 2100-surface conditions compared to present-mixed conditions. Given the restrictions set by the experiment, the uncertainties in climate change projections as well as the effects of climate change on the marine ecosystem, the qualitative conclusion from this investigation is that the risk of harmful dinoflagellate and raphidophyte blooms will increase rather than decrease due to climate change. (C) 2003 Editions scientifiques et medicales Elsevier SAS. All rights reserved.