The phytoplankton diversity was higher in the Kattegat than in the Skagerrak. In the Kattegat there was an obvious impact of the Baltic blooms considering the presence of cyanobacteria surface accumulations that had drifted out through the Sound. There were relatively high cell numbers of the coccolithophorid Emiliania huxleyi in the Kattegat and Skagerrak samples.
The integrated (0-20 m) chlorophyll concentrations were above normal at Å15, and within normal for this month at all other stations. In the southern and eastern Baltic, there were few or none filamentous cyanobacteria in the samples. There were, however, high cell numbers of the dinoflagellate Prorocentrum cordatum at BY2. At BY15, BY38 and at REFM1V1, the amounts of cyanobacteria were high, and surface samples at BY10 and BY32 did have a dominance of the potentially toxic cyanobacterium Nodularia spumigena*. The integrated (0-20 m) chlorophyll concentrations were above normal at BY32 and BY38, just below normal at BY2 and within normal for this month at all of the other Baltic stations.