Summary
The phytoplankton diversity was generally low in the Kattegat and Skagerrak areas. Rather small chlorophyll fluorescence peaks were caused by a few diatom species and the dinoflagellate genus Ceratium. The summer bloom of cyanobacteria was ongoing in the Baltic Sea. Aphanizomenon flos-aquae dominated in the samples and at most stations there were just a few filaments of the potentially toxic species Nodularia spumigena*. N. spumigena* was the most abundant at REF M1V1 and at BY38. Small patches of surface accumulations were observed between BY29 and BY20, between BY38 and BY32 as well as northwest of BY15. Chlorophyll fluorescence peaks at the Baltic stations were caused by the potentially harmful algae group Prymnesiales* and colonies of pico cyanobacteria.