January 1997, at monthly mean temperatures between +0.5 °C and -1.0 °C, was clearly colder than in previous years. February and March were too warm, compared to the long-term mean. The cold anomaly of sea surface temperatures continued in January. Values returned to normal in February and even exceeded the long-term mean in March. Measurements of nutrient distribution in the German Bight showed a decrease in the phosphate concentration to only 50 % of 1990 levels. The sum of inorganic nitrogen compounds was found unchanged, and the silicate concentration had changed only negligibly.
There was no unusual plankton development. The typical seasonal development of Odontella aurita was observed in January and February in the northern part of the Sylt Wadden Sea. In winter plankton off Helgoland in March, Coscinodiscus concinnus replaced Coscinodiscus wailesii, as in the year before, but the abundance of this diatom species was lower than 1996. At the end of April, large flagellates became more abundant. Growth of the foam-producing alga Phaeocystis globosa was slow. In the Schleswig-Holstein Wadden Sea National Park, the decline in the occurrence of green algae continued. Sea grass was at the same low level as in 1994 and 1995.
An investigation in the German Bight showed that another weak recruiting year-class of cod developed in 1996. Haddock, whiting, and smelt developed favorably.
January showed a markedly negative temperature deviation. Mean temperatures ranged between -0.8 °C and -2.0 °C. February was too warm, at temperatures between 3.0 °C and 4.5 °C. In February, nutrient concentrations in the coastal waters of Mecklenburg Vorpommern and in the Baltic Proper were lower
than in previous years. The low oxygen levels in the Bornholm Basin, Gulf of Gdansk, and eastern Gotland Basin will decrease further toward the summer of 1997. In early April, only few diatom species were observed off the Schleswig-Holstein Baltic coast. Some flagellate species prevailed. Very high chlorophyll-a levels were measured in the coastal waters of western Mecklenburg-Vorpommern in February. Nothing unusual was observed in the inner coastal waters. In the southern Arkona Sea, the spring vegetation period started in the first decade of March, in line with long-term observations. An unusual observation was an extraordinary algal bloom in the Kattegat in January.
A considerable decrease was observed in the strong 1994 cod year-class, compared to the year before. The weakness of the 1995 year-class was confirmed. The strong 1996 year-class will be important for fisheries. Plaice catches were lower than in 1996, and dab stocks declined as well.