The mesozooplankton in the wadden sea of Sylt (North Sea)

Kurzfassung

Untersuchungen der Anzahl und Biomasse der wichtigsten Zooplankter (>150 µm) im Sylter Wattenmeer von März bis November zeigten, daß auch im Wattenmeer mit seinem hohen Anteil meroplanktischer Larven die holoplanktischen calanoiden Copepoden stets dominieren. Vier Copepodenarten bildeten im Mittel 85% der Zooplanktonbiomasse. Lediglich von Juni bis September waren andere Gruppen nennenswert vertreten, vor allem Polychaetenlarven (15% der Biomasse von Juli bis September), harpacticide Copepoden und Appendicularien.

Summary

• 1. Abundance and biomass of the quantitatively most important zooplankters (>150 µm) were investigated in the wadden sea between the island of Sylt and the North Frisian Coast from March until November, 1972. Zooplankton screened from 10 l surface water samples twice daily was counted under the microscope and calculated zooplankton carbon was taken as biomass measure.

• 2. In spite of the large number of meroplanktonic larvae present, calanoid copepods(Acartia clausi, Centropages hamatus, Temora longicornis andPseudocalanus elongatus) dominated with an average of 85% (including copepodites) of the zooplankton biomass (7.4 µg Cl⁻¹). The great fluctuations in copepod stocks were not related to hydrographical changes during summer and autumn.

• 3. The copepod concentrations recorded were about one order of magnitude higher than those published from neighbouring wadden sea and coastal waters using plankton nets.

• 4. Only from June to September, other zooplankton groups were of quantitative significance, mainly the polychaete larvae, which made up 15% of the zooplankton biomass from July to September. A mass occurrence of harpacticoid copepods was restricted to the beginning of June until the beginning of July. Appendicularians were abundant from July to September.