At mean temperatures between 5.0 and 6.0 °C, the second warmest February of the century was recorded this year. Above-average temperatures were also recorded in January, March, and April. Sea surface temperatures were up to 1.3 K above the long-term monthly means.
The spring bloom of the foam-producing Phaeocystis alga which, quite unusually, had not been observed off the island of Norderney in the past two years occurred again this year. The time of occurrence, mid-April, was in line with expectations based on long-term observations. The light-producing Noctiluca scintillans was found to be very abundant off Helgoland as early as mid-April.
"Red tides" were also reported from other areas of the German North Sea coastal waters. At the end of April, concentrations of more than 1000 cells per liter were observed, exceeding the maximum seasonal values measured in the past two years. At almost all stations, there was a clear predominance of rod-shaped plankton consisting of Rhizosolenia summer species (diatoms).
In mid-May, Chattonella concentrations at the west coast of Schleswig-Holstein, though elevated at 0.17 million cells per liter, were not yet alarming. In the Danish waters off Fanø, the fish toxic alga Chattonella reached concentrations of 5 million cells per liter. While no fish kills were observed in German waters, mass mortalities of both wild stock and culture fish (salmon farms in south Norway) occurred in south Norwegian, west Swedish, and Danish waters.
On the coasts of Mecklenburg-Vorpommern, the phytoplankton bloom which normally begins in March was observed as early as January and at the beginning of February. By March, the phytoplankton bloom in the Mecklenburg Bight had disappeared.
Despite the positive temperature anomaly, phytoplankton growth in the southern Arkona Sea started as late as mid-March, which is not much earlier than the long-term mean. In mid-May, small flagellates prevailed on the east coast of Schleswig-Holstein which was normal for the season. The predominant species in the bodden waters at this time was diatoms.