The plankton of the North Sea-pelagic ecosystems under stress?

The classical marine pelagic foodweb description was ascribed to the North Sea in the 1920s; phytoplankton production supports planktonic animals such as the copepod crustacean, Calanus, which in turn feed herring and other pelagic fish. Later studies have shown how organic material not consumed in the water column supplies benthic communities and demersal fish. This paper examines the pelagic ecosystems of the North Sea. They are stressed by: (1) fisheries pressure on higher trophic levels; (2) anthropogenic enrichment with nitrates and phosphates, which encourages the blooming of some types of phytoplankton; (3) climatic change; (4) input of toxins. Difficulties in obtaining and interpreting evidence of change are reviewed. Observational evidence of change can be supplemented by understanding the nature of the pelagic ecosystem and its links with physical conditions in different parts of the North Sea. Two regions of the North Sea are examined and compared.