Summary
Diatom species, often blooming during summer, were rather abundant in the Kattegat and Skagerrak samples. These summer species, as well as the diatom Chaetoceros danicus, also dominated in the samples from the chlorophyll fluorescence maxima. The flagellate Emiliania huxleyi is blooming in the North Sea, visible in satellite images: https://lance.modaps.eosdis.nasa.gov/imagery/subsets/?subset=Southern_Norway_and_Sweden.2016151.aqua.250m. The cell surface of E. huxleyi causes a bright turquoise coloring of the water when blooming. The species has reached Skagerrak and Kattegat with the currents. It is not harmful. The integrated (0-20m) chlorophyll concentrations were above normal for this month at Anholt E and N14 in the Kattegat and at Å15 in the Skagerrak, and within normal at the other stations. The species diversity was quite low in the Baltic Sea which is normal for the month of May. The amount of pico cyanobacteria colonies was high though, and the flagellate cf. Prymnesium polylepis was present at many stations. The threadlike cyanobacterium Aphanizomenon flos-aquae was present in most samples, and the highest cell counts of the species was found at BY38. The integrated (0-20m) chlorophyll concentrations were normal for this month at all stations in the Baltic except at REF M1V1 where it was below normal.