ARK and Ørsted release oysters to restore biodiversity at wind farms

ARK Rewilding Netherlands and Ørsted released five cubic meters of old oyster shells overrun with five million juvenile oysters in ‘Voordelta 05’.

The partners’ goal with this initial pilot is to determine the most effective ways to start large-scale marine nature development both inside and outside of wind farms.

Together, ARK and Ørsted are bringing back sizable, living reefs to increase biodiversity. For this pilot, freshly created oyster baskets and nearly extinct European flat oysters were utilised.

Shellfish reefs are valuable to the ecosystem. For many species, they serve as spawning and nursery grounds, as well as food and shelter. Clearer water is produced by reefs, which filter the water and trap mud. As a result, more sunlight can reach deeper into the water, allowing for greater algae growth. Algae form the foundation of the marine food cycle and sequester carbon.

The work being done at the Voordelta, the coastal area separating the provinces of South Holland and Zeeland, is a first step for more extensive reef operations. Reefs are less prone to pests or sand cover when they are large and healthy. Large reefs have a better chance of repairing storm or winter damage.

Up to the end of the nineteenth century, clam reefs covered 30% of the North Sea’s floor. Since then, the reef has lost 25,000 square kilometers. Recovery won’t happen naturally since there isn’t enough brood in the water and the bottom is too sandy and disturbed for oysters and other species that construct reefs to settle. Using larvae that flowed from the Grevelingen, a natural oyster reef was found in the Voordelta in 2016. As a result, the area is suitable for oysters and a good location to test out solutions.

Old oysters covered in baby shells have been a test subject for ARK Rewilding Netherlands for a number of years. The partnership with Ørsted enables experiments to be conducted on a wider scale, farther from the coast, and eventually, in deeper water. The objective is to build reefs that can endure the North Sea’s swell and are significant ecologically.

Largest expansion

The Sea Shell Foundation’s breakthrough in oyster farming last year, which enabled it to successfully raise millions of oyster larvae through to the point when they settle and create shells, contributed to this week’s expansion being the largest to date. Bonamia-free and bonamia-resistant parent oysters are used in the breeding station for this. In addition to overfishing, bonamia is a disease that helped bring the wild European oyster dangerously close to extinction.

An entirely new kind of oyster basket has been used in order to facilitate scaling up for reef restoration. Compared to earlier “oyster cradles” and “oyster bags,” these are simpler to manage on board. The new structures, however, are built of untreated wood pallets and ungalvanized wire mesh, which are both biodegradable materials. For instance, the structures that keep the oysters together, defend them from predators, and protrude above the sand do not need to be fished up again later. Additionally, there is no CO2 released during the construction of concrete artificial reefs.

Since ARK Rewilding Netherlands’ tests began, the most baby oysters have been released during this week’s promotion. In comparison to prior years, the starting shells are smaller. The strategy they’ll use is intriguing. Later in the year, monitoring will reveal.

Image source: Gwenael Hanon

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