In the North and Baltic Sea regions, sunshine hours in May exceeded the long-term mean by 10 - 20 % and, therefore, the mean air temperatures in May and June, at 12.0 - 13.9 °C and 14.2 - 16.7 °C, respectively, were higher than average (1 - 2 K higher). Also the mean sea surface temperatures were at least 1 K above
the long-term monthly mean.
After the breakdown of the spring algal bloom, the first colonies of the foam-producing alga Phaeocystis globosa were observed off Sylt, with a short-term mass production in mid-May after which cell concentrations dropped to a very low level. However, on the west coast of Schleswig-Holstein, concentrations still continued to increase in early June. The light-emitting alga Noctiluca scintillans continued to be abundant and in some area mass developments were observed, with the occurrence of several "red tides" reported by Zentraler Meldekopf Cuxhaven. Concentrations of other dinoflagellates were unusually low for the season. As expected, the prevailing diatoms in June were rod-shaped plankton species (Guinardia flaccida, Rhizosolenia shrubsolei).
Densities of green algae on the coast of Lower Saxony were rather low. Marked growth of green algae was observed only in the Wadden Sea of Baltrum.
Hydrogen sulfide was found in the entire Bornholm Basin in the bottom layer, and below 100 and 150 m in the Danzig Bay and entire Gotland Basin, respectively. Phytoplankton abundance in almost all areas of the western and eastern outer coastal waters was relatively low, with a narrow range of species, which is untypical of the season. The group of small flagellates was dominant, in accordance with the season. Also diatoms were observed sporadically. At the measuring point "Seebrücke Heiligendamm", a summer bloom of diatoms occurred in early June, which has been rarely reported in this sea area before, in contrast with the western Baltic. The Pomeranian Bight also differed from the other areas in that a wide range of species was present and the total volume (5.3 mm³/L) clearly exceeded the long-term monthly average. Potentially toxic plankton species identified along the outer coasts of Mecklenburg-Vorpommern were the filamentous blue-green algae Aphanizomenon baltica (0.2 mm³/L and Planktothrix agardhii. In the Stettiner Haff, high concentrations of Aphanizomenon baltica (36.2 mm³/L) were measured. Unlike the outer coastal waters, the inner coastal waters (Greifswalder Bodden and Strelasund) showed increased cell concentrations of a small, centric diatom which could not be precisely identified. In the bodden waters, mass developments of filamentous brown algae
(Pilayella litoralis) along some sections of the coast caused spoiling of some beaches, but to a lesser extent than in previous years.