Phytoplankton
Primary production is highest in the coastal regions due to nutrient inputs from the rivers and mixed water columns. This production was higher during the 1980s as a result of eutrophication. Primary production in the coastal zone decreased with the decline of the phosphate input in particular.
Zooplankton
The northern North Sea was, until recently, a cold-temperate boreal province, which, after the late 1980s regime shift, became a warm-temperate province. Zooplankton communities in the northern North Sea are generally comprised of Atlantic and offshore species (such as Calanus finmarchicus and Metridia lucens) as these waters are stratified during summer months (image B). The zooplankton community of the southern North Sea primarily consists of neritic and coastal species (such as decapod larvae Centropages hamatusand Calanus helgolandicus) which are well-suited to the mixed waters of this region. For the most part changes in plankton in the southern North Sea are driven by climatic variability. Population of the previously dominant copepod Calanus finmarchicus has declined in biomass by 70% since the 1960s. Species with warmer-water affinities, e.g. Calanus helgolandicus, are moving northward to replace Calanus finmarchicus but are not abundant. Over the last few decades, climate warming in the southern North Sea has been noticeably faster than in the northern North Sea (due to the southern North Sea being shallower). This is reflected in the biological response of planktonic organisms; for example, phenological cycles observed in the southern North Sea have moved further forward in time than in the northern North Sea. A new invasive copepod species, Pseudodiaptomus marinus(originating from east Asiatic waters), was found in the southern North Sea in 2011.
