Jan De Nul, 19 July 2025 - About 30 kilometres off the coast, the BELREEFS consortium has planted 200,000 young oysters on the seabed. Commissioned by the Marine Environment Service (FPS Public Health), BELREEFS is working to restore the once abundant oyster reefs in our sea. The reefs are an important habitat for numerous other marine animals and thus contribute to strengthening biodiversity. This project is part of broader government efforts to address the poor state of the marine environment by actively focusing on nature restoration.

BELREEFS is a collaboration between Jan De Nul, the Institute of Natural Sciences, Shells & Valves and Mantis Consulting. They installed more than two hundred thousand young oysters on the seabed of the North Sea. Before 1900, European flat oyster beds (Ostrea edulis) were ubiquitous in the North Sea. Overfishing and human activity on the seabed have caused them to disappear almost entirely. A persistent parasite also wiped out the last flat oysters in the 20th century.

However, they are extremely valuable habitats. Flat oysters are also known as ecosystem engineers because they form reefs that serve as shelter and food sources for many other species. In this way, they support diverse fish species and enhance biodiversity. They also provide us with all kinds of other ecosystem services. They purify the water and capture (excess) nitrogen. Closer to the coast, they also stabilise the seabed, which makes us more resilient to the effects of climate change.

Biodegradable, hard material

After more than a year of preparation, the oysters were lowered into the water from an installation vessel, attached to what is known as reef substrate. The project team studied various biodegradable materials that could serve as reef substrate and ultimately opted for baked clay bricks. Oyster larvae were sown on these bricks and cultivated for several weeks. This was done partly in a nursery in the Netherlands, but in Ostend, the team is also developing techniques to do this locally, close to the ship's departure point.

Old shipwreck

The oysters were installed on a gravel bed thirty kilometres from the coast, around the legally protected shipwreck Kilmore, at a depth of 30 metres. The project team chose this location with care. They mapped out the locations with the most suitable seabed and environmental conditions to maximise the chances of survival. Natural protection against damage and currents, and optimal conditions for installation, are also important parameters. They also consulted with the fishing industry via the Redercentrale (Shipping Association) to determine the best location for the oyster reef.

Intensive monitoring

After installation, an intensive monitoring programme will be carried out to track the development of the reef and its effect on biodiversity. The monitoring will evaluate the ecological impact and provide crucial insights for the informed management of the restoration area, as well as for the further development of future upscaling plans.

European law for nature restoration

The BELREEFS restoration project is one of the federal measures resulting from European directives to improve the environmental status of our seas. The project is supported by the LIFE project Belgium for Biodiversity, which aims to strengthen biodiversity in Belgium.
 

Applications of unique know-how

The knowledge and techniques developed during BELREEFS have broader applications in active nature restoration — for example in Natura 2000 areas — but also in the nature-inclusive design of offshore infrastructure for renewable energy. Jan De Nul can also apply these techniques to the many wind farms and submarine cables that it helps to install.