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The unbalance of phytoplankton and copepods in the North Sea
Fransz, H.G.; Gieskes, W.W.C. (1984). The unbalance of phytoplankton and copepods in the North Sea. Rapp. et Proc.-Verb. Cons. Int. Explor. Mer 183: 218-225
In: Rapports et Procès-Verbaux des Réunions du Conseil Permanent International pour l'Exploration de la Mer. Conseil Permanent International pour l'Exploration de la Mer: Copenhague. ISSN 0074-4336, more

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Keyword
    Marine

Authors  Top 
  • Fransz, H.G.
  • Gieskes, W.W.C.

Abstract
    Estimates of phytoplankton and copepod standing stock and productivity are plotted against date to present seasonal production cycles in different areas of the North Sea. The data used were obtained during cruises in the Southern Bight and at the Oyster Ground and the Fladen Ground between 1971 and 1981. It is concluded that the delay between copepod production and primary production, which is most distinct in spring, excludes any possibility of all phytoplankton being directly eaten by copepods. At times much of the crop may sink to the bottom or be consumed directly by protozoa and bacteria. During the summer months copepod grazing matches primary production in all areas. Only during that period does a limitation of copepod growth by food scarcity and a high grazing pressure on phytoplankters seem to maintain a balance between phytoplankton and zooplankton. The unbalance between the phytoplankton and the herbivorous mesozooplankton in spring and autumn must lead to a loss of energy potentially available to the higher trophic levels. Either the copepod production (about 10g C m-2 yr-1 in the south to at least 20g C n-2 yr-1 in the north) is sufficient to sustain the fish production, or there is an important additional food chain to the top carnivores through herbivores and herbivores near or at the bottom.

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