The return of Dutch oyster beds

Sustainable and safe oceans and inland waterways

Oyster beds provide a place for other organisms to live, shelter and breed. Video: Shutterstock

Estimated reading time: 8 minutes

Shellfish are incredibly important: not only are they a source of food, but they can also help save the climate. However, Dutch oyster beds have suffered heavily from overfishing and disease. That is why researchers at Wageningen University & Research are involved in a European project to study the options for achieving shellfish populations that are healthy and climate-proof.

Oyster beds provide a place for other organisms to live, shelter and breed. They are therefore beneficial for marine ecosystems. Furthermore, the fact that oysters need calcium carbonate for their shells means they could play a role in sequestering carbon in the sea. And oyster reefs could act as breakwaters that grow in line with rising sea levels, explains Pauline Kamermans, a senior researcher in marine ecology and aquaculture at Wageningen University & Research (WUR). Such nature-based solutions (NBS) are at the heart of FutureMARES, a European project set up to investigate the relationships between climate change, marine biodiversity and ecosystem services. Kamermans is the WUR project manager. The activities revolve around three nature-based solutions for the effective recovery, effective maintenance and sustainable harvesting of marine resources. The three nature-based solutions are interconnected: if the oyster beds grow well then oysters can be harvested for human consumption, for example.

Oyster reefs have a fantastic effect on biodiversity

Measurements of the water composition are carried out in the cube. Photo: Emiel Brummelhuis

The project involves 33 partners, each with their own studies. The Norwegians, for instance, are examining the interrelationship between kelp, sea urchins and cod, while Spain is considering how to restore fields of seagrass off the coast. The Netherlands focuses on the effective restoration and sustainable harvesting of shellfish stocks. WUR knows a great deal about aquaculture in general and oysters in particular.

Exotic species

Kamermans specialises in shellfish. In this project, she and her colleagues are studying the Dutch flat oyster and the pacific oyster, an exotic species. While most ecologists are not keen on such alien species because of their tendency to drive out indigenous species, they can sometimes play a positive role in an ecosystem. That might be the case for the pacific oyster in the Zeeland delta. The Dutch flat oyster there has disappeared almost entirely, mainly because of the extremely cold winter of 1962-1963, but also due to centuries of fishing and the inadvertent introduction of a parasite that came with a cargo of oysters from France. But the pacific oyster is not susceptible to this parasite. Kamermans: “Various parties are trying to reintroduce flat oysters in the North Sea. That is not just because we like to eat them but also because oyster reefs on the North Sea bed have a fantastic effect on biodiversity, just as they do in the Zeeland delta.”

Disease-free oysters

Kamermans is investigating ways of creating healthy populations of Dutch flat oysters. In partnership with the oyster company Roem van Yerseke and the foundation for marine aquaculture Stichting Zeeschelp, the Wageningen Marine Research scientist is using disease-free, resistant oysters from the Zeeland delta to breed more oysters that are free of disease. Previous research showed that the flat oyster can benefit from the presence of its pacific relative, because the flat oysters prefer to use the remains of the shells of the pacific oyster as the material to which they attach themselves. “However, we have not yet been granted permission to place these shellfish in the North Sea. That is why we are taking adult oysters from Norway to put them back in the North Sea. They come from a disease-free area.”

The activities revolve around three interlinked nature-based solutions for the effective recovery, maintenance and sustainable harvesting of marine resources. Illustration: IRD MARBEC

But it is not clear how well the Norwegian oysters will be able to cope with the higher temperatures. The seawater around Norway is much colder than the North Sea. Moreover, temperatures are rising in the North Sea because of global warming. So Kamermans is doing lab experiments for this project in which she exposes Dutch and Norwegian flat oysters to heatwaves. “The oysters are in buckets in our climate chambers. We use a heart-rate meter developed by our Portuguese FutureMARES partner to test whether they experience stress as temperatures increase. We want to find out how they respond to heatwaves and to slowly rising temperatures, and how hot it can get before they die off.” The partner in Southampton in the UK will then look at the genetic composition of the two populations as a result of the heatwaves in order to draw conclusions about their ability to adapt. The lab experiments have only just started, so there are no results to report as yet.

Carbon sequestration

Kamermans is also monitoring the pacific oyster in the Eastern Scheldt estuary. She is studying the effect the oyster has on the amount of carbon in the water. If oysters really do remove carbon from the seawater and sequester it in the seabed, they could play a role in reducing CO₂ levels.

We want to find out how warm the water can get before the Norwegian oysters die off

Cuboid covers are placed over the oyster beds to measure the carbon content of the water. This is being done to see whether the pacific oyster can reduce CO₂ levels. Photo: Tilman Meyer-Clasen

Kamermans: “We have just carried out our first set of measurements in the field together with the Royal Netherlands Institute for Sea Research (NIOZ). We do that by placing cube-shaped covers over the oyster bed, and elsewhere as a control, and measuring the composition of the water inside the cubes. Interestingly, our FutureMARES partner in Israel is doing similar experiments, only with domes rather than cubes. I can’t wait to see their results, although it is too soon to make comparisons yet.”

Oyster beds in wind farms

Wind farms are being considered for the construction of new oyster reefs in the North Sea as fishing boats are not allowed in the wind farms and so the reefs will be undisturbed. The Ministry of Agriculture, Nature and Food Quality is also interested in this use of wind farms. The ministry would like to know whether it is possible to cultivate shellfish or seaweed at these sites, and if so on what scale. The Ministry of Agriculture also approves of plans to restore flat oyster populations because of its philosophy of encouraging biodiversity in Dutch waters. Kamermans: “We will be sowing oyster seed (baby oysters) and putting down empty oyster shells because the oyster larvae need something hard to attach themselves to. We hope this will turn into a reef that grows further of its own accord.

In the FutureMARES project, the Dutch water research institute Deltares will perform calculations for various options, for example to see what would happen if half the wind farm was used for oyster beds and the other half for growing seaweed. Deltares will also calculate whether the different scenarios provide enough nutrients for the oysters and whether enough food is left over for other marine creatures. Kamermans: “For example, when oyster numbers get above a certain level, you see a decline in the amount of plankton. That can have a negative impact on the ecosystem. So you can’t just carry on creating more and more oyster beds.” The FutureMARES project is due to run until the end of 2024. It is too early at present for results and Kamermans does not want to make any predictions at this stage. “However, you can say that oysters are extremely important from numerous perspectives. They may be able to help save the climate and serve as a source of food, not just for us but also for many other living creatures. That is why it is so important for Europe to consider shellfish.”

European research context

FutureMARES addresses the following European policy challenges:

  • Protecting biodiversity
  • Protecting coasts in the face of climate change

Wageningen University & Research groups involved: Wageningen Marine Research and Wageningen Economic Research European and other countries involved: Belize, Chile, Denmark, Finland, France, Germany, Greece, Israel, Italy, the Netherlands, Norway, Portugal, Spain, Sweden and United Kingdom

Duration: 2020 – 2024

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