First monitoring of oyster reef restoration pilot: survival rates encouraging and opportunities for improvement

Last summer, stones with young flat oysters were deployed for the first time in the Port of Rotterdam. These stones had been “seeded” with oyster larvae using an innovative technique known as remote setting. Recently, researchers returned to the site for the first time to assess how many oysters had survived the first months after deployment.

“The findings, following further analysis, are actually very positive,” says Pauline Kamermans, marine ecologist at Wageningen Marine Research. She is project leader of the so-called RESO project, in which nine partners collaborate. “The number of living oysters we found comfortably meets the international OSPAR definition of an oyster bed.” According to Pauline Kamermans, however, this does not mean there is now a reef. “A reef is more than an oyster bed: it contains more oysters per square metre, which reproduce themselves and therefore grow on top of one another’s shells.”

The results of the first monitoring survey provide insight into where further improvements can be made. Many of the oysters that were no longer alive had shown little or no growth since the day they were deployed. It is possible that they did not survive the transport or the placement on the seabed. “Last year was the very first time we had ever applied this method. That is precisely why this monitoring survey was so valuable. The results provide us with clear indications of where we can make improvements,” says Pauline Kamermans.

Among other measures, the partners will improve monitoring of the factors that influence how oyster larvae settle on the stones, for example by tracking temperature and food availability more accurately. By increasing the number of young oysters on the stones, the consortium also hopes to keep more of them alive in the North Sea. The partners are also examining how the transport and deployment of the stones can be improved so that more young oysters survive. The next deployment of ‘oyster stones’ will take place later this year at two TenneT cable crossings, further offshore.

The consortium is developing this reef restoration method because reefs are crucial to life in the North Sea but are now extremely rare. Oysters build these reefs, making them one of the richest ecosystems in the North Sea. Reefs provide shelter, habitat, feeding grounds and breeding areas for a wide variety of fish species, seaweeds, rays and even seals and small cetaceans. In addition, reefs improve water quality.

Through the development of remote setting on stones, the consortium is investigating how reef restoration can be intelligently linked to the construction of maritime infrastructure such as offshore wind farms and cable crossings. By enabling oysters to settle directly on stones and subsequently deploying these where hard substrate is required, the partners aim to bring large-scale nature restoration one step closer.

In the remote setting pilot (the RESO project), nine companies, knowledge institutes and nature organisations are working together: Wageningen Marine Research, Wageningen University, ARK Rewilding Nederland, Stichting Zeeschelp, Waardenburg Ecology, Van Oord Ocean Health, TenneT, Port of Rotterdam Authority and De Rijke Noordzee. De Rijke Noordzee is a collaboration between Stichting De Noordzee and Natuur & Milieu.