Baby oysters found on oyster tables at Borssele III/IV wind farm

It’s time to celebrate! The flat oysters introduced to the Borssele III/IV wind farm in 2020 have reproduced. This was revealed when the oyster tables — artificial oyster reefs — were lifted out of the water to be studied for the first time in two years. And this isn’t the only positive finding.

Borssele III and IV

The Borssele III/IV wind farm, constructed and operated by Blauwwind, is located about 55 kilometres off the coast of Vlissingen, the Netherlands. The wind turbines generate enough energy to supply 825,000 Dutch households with green electricity. Although offshore wind farms play a vital role in the transition to clean and sustainable energy, biodiversity conservation and nature enhancement are also important. That’s why, in 2020, Blauwwind and The Rich North Sea joined forces with Eurofins to launch a restoration project for flat oysters, a species native to these waters.

Research overview

In 2020, oyster tables — artificial oyster reefs — were installed.
In 2021, shell material was added to help oyster larvae settle. The oyster tables were lifted out of the water to be examined for the first time.
In 2023, the oyster tables were analysed for a second time. The research findings are discussed in this article.

Image: Eurofins Aquasense

Oyster tables for a thriving marine ecosystem

Oyster tables, containing more than 2,400 flat oysters in total, were introduced at various sites in the Borssele area. To encourage oyster larvae to settle, shell material was later added. The restoration project aims to not only restore the flat oyster population in the Dutch North Sea but also promote biodiversity within the wind farm and nearby. Marin van Regteren, a marine ecologist at Eneco, is involved in the project and says, “We are hoping that natural oyster reefs will eventually form.”

Gaining comprehensive insight

The researchers were primarily interested in oyster survival rates and reproduction status. They also inspected the oysters for parasites (Bonamia ostreae) and looked at how well oysters are settling on the layers of scour protection and shell material around wind turbine foundations. In addition, the researchers used cameras on remotely operated vehicles (ROVs) and eDNA analysis to record marine life in the area. “We wanted to gain comprehensive insight into biodiversity at the wind farm”, explains Marin.

Key findings

Average survival rate of flat oysters: 70%
Percentage of oysters ready to reproduce: 88%
Oyster parasites: not found
Oyster spat (baby oysters): found
Total number of species identified at the wind farm: 128

Image: Eurofins Aquasense

Baby oysters and 128 species found

The presence of baby oysters is the standout finding. “Yes! We found oyster spat, or baby oysters, in multiple locations where we took water samples”, says Marin. “And most of the oysters we examined were almost ready to release their eggs into the sea.”

The researchers also looked at biodiversity within the wind farm using photo and video analyses, scrape samples and DNA analysis of water samples. They found no fewer than 128 species in total. Marin adds, “We are talking crabs and lobsters, various species of fish, worms, seabed animals, anemones, starfish… you name it.”

Scour protection as oyster habitat

Marin says that scour protection around the wind turbines plays a key role in the project: “The North Sea has a sandy seabed that would erode rapidly if monopiles were just driven into it. That’s why two layers of rocks are placed around the foundations — a filter layer of small rocks topped with an armour layer of larger rocks. We added shell material at eight locations, as oysters prefer to settle on other shells.”

Promoting all marine life

These layers of shells are rich in calcium carbonate. “This makes oyster larvae go, ‘Hey, there’s a lot of calcium carbonate here, so this is the place to be’”, explains Marin. If enough oysters do this, a natural oyster reef will eventually form. “That was our goal when we added the shell material in 2021. And it still is.”

Marin notes that scour protection also attracts a variety of marine animals: “It offers a resting and reproduction area for fish, which, in turn, draws other marine animals like sharks, rays and seals.”

New research in 2028

So far, the oyster tables have been a resounding success. What’s next for the project? “We now know that these layers of rocks and shells attract marine life”, says Marin. “It will be interesting to see how this develops over the years.”

The offshore wind farm is attracting animals and organisms, but Marin hopes it will eventually become a source of new marine life “with fish and other species coming here to spawn. In 2028, we will return to study the oyster tables and analyse biodiversity.”