Onboard the Belgica

It is generally considered that the seafloor of Belgian part of the North Sea consists chiefly of sand or mud. This view is incomplete : natural stony grounds are found around the Westhinder bank, some 25 km off our coasts.

Edouard Van Beneden, a biologist of University of Liège, was a pioneer of the Belgian marine research. In 1883, he gave the following description of the fauna of this area (translation of the original French text):

Underwater picture of a large cobble and its associated fauna

The dead man’s fingers, Alcyonium digitatum (a soft « coral »)

“It seems that a real bank of rounded cobbles exists. This rocky area […] is probably known by English fishermen who harvested the horse-foot oyster along our coasts at certain periods.” (NB. This is the famous “flat” oyster Ostrea edulis, the banks of which were overexploited in the 1870s). […] “In these places, the sea bottom is literally covered with a dense forest of sponges, hydroids, sea anemones, dead man’s fingers, bryozoans, tunicates and molluscs, all living tight to each other, and even interpenetrating.” […]. “I must acknowledge that I have never witnessed a single dredge tow bringing such a quantity of different animals onboard”

A first answer to these questions is given by the large amount of marine organisms collected by G. Gilson, a former director of our Museum, during his explorations some 20 years later (1900 – 1910). Thanks to the digitization effort performed by our team, we are now able to study the collection’s content. We confirm the old views of Van Beneden and others. But there is more: we can locate these grounds with a good precision.

Cobbles of various sizes...

... and sometimes really big !

What is their status nowadays? To answer these questions, we tracked the steps of these pioneers around the Westhinder bank onboard the R/V Belgica between 13 and 24 June 2005. And yes indeed: tons of pebbles and cobbles of various size and origin have been brought onboard thanks to a small robust beamtrawl.

What are our first results? No surprise regarding the natural banks of the flat oyster: the species is almost extirpated from the North Sea and we could only find back shells, evidencing the former presence of banks on some locations. Other species abundant in Gilson’s collection were surprisingly not found back (as is the case for the hornwrack Flustra foliacea). Fragile attached animals such as anthozoans, bryozoans, hydrozoans and sponges, which are typical of such bottoms, were generally of modest size and less abundant. We observe a fragmentation and an impoverishment of the biological richness of the area.

The 2 meter beamtrawl used for this special harvest.

The sea horse (hippocampus hippocampus).

The biological communities inhabiting these bottoms are very different from those of sandy or muddy areas which dominate the southern bight, e.g. they host higher numbers of species. We made two unexpected findings as well: the sea horse (Hippocampus hippocampus), and the boring mussel Barnea parva, not yet recorded in our marine area. A team of scuba-divers joined this campaign to provide the first underwater pictures and films of this poorly documented area. They confirmed the old vision of a “cobble field” suggested by Van Beneden and Gilson.

In brief : this first campaign confirms the evidences provided by old texts and highlights the ecological value of the Westhinder area. The fact that naturalists ignored it for so long is surprising when one knows that Gilson himself already suggested to protect it in 1921. Isn’t this 85 years old suggestion still valid in the present era of "sustainable development"?

Barnea parva, a boring mussel, not mentioned in Belgian waters so far.

This research is carried out in the framework of the project « The Hinder Banks : yet an important region for the Belgian marine biodiversity ? », and is funded by the Belgian Federal Office for Science Policy, programme « SPSD2 : global change, ecosystems and biodiversity ». Underwater pictures reproduced with kind permission of J. Mallefet, coordinator of the project « BeWreMaBi : Belgian Shipwrecks : hotspots for marine biodiversity » (funded through the same programme).
Other pictures : Jean-Sébastien Houziaux, Francis Kerckhof (MUMM) and Michael Fettweis (MUMM).