Defended PhD by Karl Van Ginderdeuren: mesozooplankton in the southern North Sea | Marine@Ugent

Defended PhD by Karl Van Ginderdeuren: mesozooplankton in the southern North Sea

The pelagic zone, i.e. the water column from the surface to the bottom of a water body, constitutes the biggest habitat in the world. This water body is not only big, it is also of very high ecological importance, since a vast majority of aquatic species, and more specific fish species, spend at least part of their life in this zone, either as larvae or as adults. The zooplankton -i.e. animals that passively drift in the water column- is typically found in the pelagic zone worldwide.


An update on zooplankton dynamics in the Belgian part of the North Sea (BPNS) is certainly in place: most recent data on the community structure and composition of the zooplankton date from the 1970s, and no thorough studies existed on the feeding ecology of small pelagic fish in the BPNS.


The overall aim of this PhD study was to expand and update our knowledge of the mesozooplankton (0.2-2 mm) in the southern North Sea, and to characterize the trophic role of zooplankton as prey for pelagic fish. The scientific value of this PhD study lies in the fact that we are able to link the detailed in situ plankton results directly to the pelagic fish diet.


Two years of extensive sampling delivered a lot of distribution data. In total, 137 zooplankton taxa are currently found in the BPNS. Nine zooplankton species are newly recorded for the BPNS, but we also lost the calanoid copepod Calanus finmarchicus, a species that has shifted northwards and that has been replaced by Calanus helgolandicus throughout the southern North Sea.


Stomach content analyses point out that only a limited number of zooplankton species dominate the diet of the four pelagic fish in the BPNS. Herring, sprat, mackerel (and to a lesser extent horse mackerel) show a high preference for calanoid copepods, and a selective feeding behavior towards adults and females of these copepods. Yet, we could find no proof of any bottom-up control that zooplankton might exert on the pelagic fish in the BPNS.