After the spring bloom there were mostly small cells left and a few dinoflagellates and diatoms in both Kattegat and Skagerrak areas. Several species and genera of potentially toxic phytoplankton were present along the whole west coast in April. Chlorophyll concentrations at all stations were normal for this month.
In the eastern part of the Baltic spring bloom was recorded. Station BY5 in the south also presented a small spring bloom. High cell numbers were found at BY38, between southern Gotland and northern Öland. All stations with high cell numbers had a dominance of the dinoflagellate Peridinella catenata. The filamentous cyanobacterium Aphanizomenon flosaquae was present at a couple of stations in low numbers. The integrated chlorophyll concentration (0-10 m) was above normal at BY15 Gotland deep. The rest of the eastern stations had high integrated chlorophyll values (0-10 m) but within normal for the month. At the westerly stations the chlorophyll concentrations were low due to the spring bloom the month before.