Sand banks
Description and occurrence
Sand banks occur in many places in Europe, but we find these more abundant in the southern North Sea (North-French, Belgian and South-Dutch coast and the Southeast coast of England). More than 80% of the Belgian part of the North Sea consists of sand banks: Belgium thus bears an important responsibility to protect this habitat type.
Sand banks consist of gullies (depressions), flanks and a sand bank top progressing from sludge to coarse sand. Different types of communities occur in each of these parts. The largest biodiversity in the sand banks is not found in the sand bank top but rather in the flanks and the gullies.
Reefs
Description and occurrence
Are there reefs in the Belgian coast? Two habitat types occur in the Belgian part of the North Sea that may be considered as reefs: the gravel beds and the places where the sand mason worms occur in high concentrations. Both biotopes are the "hotspots" for biodiversity in our North Sea.
The gravel beds are located far from the coast, among others, at the level of the Hinder banks and the Flemish banks. It is a very rare and endangered habitat of gravel and boulders that may or may not be clumped together in the sandy or clayey subsoil and hosts a unique and rich diversity of species of fauna and flora. These are the areas that previously were important spawning chambers of the herring. Through the use of trawl nets, including the beam trawl (a trawl net where the "beam" is kept open with a metallic cross bar), this has become a very marginal area.
The reefs that are formed by the sand mason worms (Lanice conchilega) occur in our North Sea close to the coast. By clumping together, these creatures form their own micro-habitat which in turn becomes attractive to other species. The sand mason worms are also therefore called "habitat engineers" that locally support a highly enhanced biodiversity.
Sand mason worm - Misjel Decleer photo
Threat
Various human activities, such as trawling, sand and gravel extraction, dredging, dredging deposits or the construction of offshore wind farms affect the ecological integrity of sandbank and riff habitats.