Chrysochromulina polylepis bloom in the Skagerrak and Kattegat in May-June 1988: Environmental conditions, possible causes, and effects

Report of the ICES Workshop on the Chrysochromulina polylepis bloom in the Skagerrak and Kattegat in May-June 1988, held in Bergen, 28 February - 2 March 1989.

The bloom of Chrysochromulina polylepis was first noticed on 9 May 1988, when fish in fishfarms near Lysekil on the Swedish west coast were affected. The first sign of the bloom on the Norwegian Skagerrak coast was noted in a fishfarm on 13 May 1988. The bloom developed rapidly and spread with the Norwegian Coastal Current westward in the Skagerrak. The toxicity of the algae was high and the bloom caused extensive damage to both farmed fish and natural biota, including a range of organisms such as fish, various invertebrates, and even some macroalgae.
The bloom was characterized by some people as an ecological catastrophe and received great attention by the media and the public. A large effort was spent by various institutions to carry out monitoring and research on the bloom and its ecological effects. There was, thus, a large amount of information collected during the bloom. However, since the research and monitoring had to be done on an ad hoc basis, there were obvious limitations in terms of planning and coordination. As a result of this, there are some unfortunate gaps in the available information which make interpretation of the bloom event difficult. We have in this report attempted to arrive at a plausible scenario which is consistent with observations and which may be regarded as the most likely explanation for the development of the toxic bloom of Chrysochromulina polylepis.