Summary
The phytoplankton activity was rather low in the Kattegat and Skagerrak areas. Diatoms were common in the Kattegat though, with several species observed at variable abundances. The diversity was very low in the Skagerrak area. Chlorophyll fluorescence peaks at Fladen in the Kattegat and at Släggö in the Skagerrak were partly caused by the fish killing genus Pseudochattonella*. The integrated (0-20m) chlorophyll concentrations were normal for this month. A typical post spring bloom situation was found in the Baltic, with some diatom and dinoflagellate species, ciliates, cyanobacteria colonies etc. Cell numbers were generally low. The dinoflagellate Peridiniella catenata was found with high cell numbers in phytoplankton samples from chlorophyll fluorescence peaks in the Baltic. The integrated (0-20m) chlorophyll concentrations were somewhat low in the Western Baltic, otherwise normal for this month.