Morven Robertson, UK Project Manager, presented at Coastal Futures 2018 on oyster restoration around the world.

February 07, 2018


Here is a transcript of her presentation.

Click here to see the slides.

Two years ago, BLUE embarked on an ambitious project to restore the native  oyster to the Solent Oysters are a ‘keystone’ species and are recognized as ‘ecosystem engineers’ as they provide a range of services through the hard structures they create and their biological processes. The scale and type of service provided by oysters differs depending on the species and local pressures, but some of the things they do include improving biodiversity, cleaning water, helping to remove nitrogen and other impurities, and boosting fisheries. They are also an important food source. Essentially, oysters keep our oceans healthy and resilient.

Oysters are found worldwide in places including Nicaragua, Senegal, Hong Kong and New Zealand and have supported valuable fisheries. In Europe, we can trace oysters as a food source back to the Roman times. With advances in technology and increases in the number of oyster boats, landings reached enormous scales around the world with some of the biggest recorded in Europe. As late as 1978 15 million oysters were landed in in the Solent.

Unfortunately, as was the case with many boom-and-bust shellfish fisheries, these enormous landings did not last. Globally we have lost 85% of oyster reefs making them one of the world’s most imperilled marine habitats. In Europe, the native oyster has declined with many fisheries collapsing and in Germany and Belgium oysters are now functionally extinct.

The loss of the oyster has not only affected the fisheries they supported but has also had implications for the wider marine ecosystems. Removal of this keystone species has led in some cases to fishery collapse, dead zones such as in Chesapeake Bay, coastal erosion, biodiversity loss and a loss of heritage. All of this has been exacerbated by climate change.

Today, oyster restoration is an accepted practice and projects are increasing in number and scale. There has been a shift from traditional drivers of restoration – getting a fishery back – to a focus on the ecosystem services that a healthy, productive oyster bed or population could provide. The Nature Conservancy has led this work and produced several guides to help restoration projects make the case for restoration of certain species of oyster.

In the United States, restoration has focused on two main species: the Eastern oyster (Crassostrea virginica) and the Olympia oyster (Ostrea lurida). Both species play different roles in their environment, but the ecosystem services provided by Eastern oysters have been quantified extremely well. Restoration efforts in the US have already been underway for 15 or 20 years. There are two main drivers which have allowed restoration to progress quickly and at a large scale. First, oyster restoration is a priority at federal and state level through the American Recovery and Reinvestment Act of 2009 and, as a result, significant funding is available to restoration projects with clear ecosystem service outputs. Secondly, there is also significant public support for oyster restoration with community groups and schools actively helping.


Case study 1 – Harris Creek Maryland

Harris Creek, a tributary of the Choptank river in Maryland, is the largest oyster restoration project ever undertaken. So far, more than $27 million has been spent on this project and two billion hatchery oysters have been reseeded. The project is part of a wider initiative to restore 11 tributaries of the Chesapeake with oyster reefs. A key aim of the project is to restore oysters to help with the removal of nitrogen, which is a big problem in the waterway. Improvements are already being seen and, by the time that the project is completed, it is estimated that across all 11 tributaries 48% of nitrogen inputs will be removed annually.


Case study 2 – Mobile Bay, Alabama

In Alabama oysters are providing a very different service – natural coastline protection. Crassostrea form dense reefs capable of absorbing wave energy and protecting fragile marine habitats behind them. By using systems such as reef balls, this project has restored three acres of oyster reef and protected 30 acres of marsh and seagrass.


Case study 3 – Matagorda Bay, Texas

For me, this is possibly the most impressive case study in the US at the moment. The restoration of oysters at Half Moon Reef has seen incredible fisheries enhancement. When researching the site, scientists found biodiversity to be 40% higher than other reefs and 19 species were being supported. One hectare of oyster reef produced 3,200 mature crabs. Most impressive however is the growth in the recreational fishery that has been attracted to the abundance of fish around the reefs, adding an estimated $690,000 to Texas’ GDP.

It is clear in the US, for the Eastern oyster, that restoration efforts have done an impressive job in quantifying the benefits of oysters.



In Europe, things are quite different. Here we have just one species – the European flat oyster (Ostrea edulis). Although we have thorough records of its decline through fisheries across Europe there is a lack of knowledge about the European flat oyster as a species and its role in ecosystems. Things are very much in the early stages. Many restoration projects are still establishing goals and looking to define success. There are also a range of barriers in Europe, including disease, difficult legislation and lack of seed supply.  Hatcheries in the US are much more advanced than they are in Europe where supply is a real impediment.


Case Study 1 – The North Sea

Something I didn’t realise when I started oyster work was that 20% of the North Sea bed was once covered with oysters – unfortunately, historic records show how bed after bed was fished out. In places like Germany, oysters have not been found for over 60 years.

Restoring the oyster to the North Sea is logistically harder due to depths of 20-30m and the need to operate within difficult marine spatial plans, but there are two projects currently attempting to do this, one in Germany and the other in Holland, both of which are at the early feasibility and pilot study stage. These pilot studies suggest that oysters can survive in greater depths.


Case Study 2 – Dornoch Firth

In Scotland, a collaboration between Heriot Watt University, Marine Conservation Society and Glenmorangie is working to restore oysters that have been absent for the last 100 years in the Dornoch Firth. The project is in its infancy but trials have shown 100% survival rates. A key element of this project is the partnership with Glenmorangie. They hope to see oysters removing excess organic waste from the distillery, thereby providing a service that the project hopes will be appealing to similar businesses.


Case Study 3 – Essex

On the east coast of England is the Essex Native Oyster Restoration Initiative, one of the more mature projects, established in 2013, which is working to restore oysters in the only MCZ designated for oyster beds. Within the MCZ they are working within a conservation box to address issues such as shell budget and lack of mature oysters. Although this is a project hoping to realise the multiple ecosystem services that a healthy bed could provide, the end goal is to have a sustainable oyster fishery in the wider MCZ.


Case Study 4 – Solent

In the Solent we arguably face an even bigger challenge – that densities are extremely low (0.01 oysters/m2), and we are without a MCZ designation for oyster beds. This has made it even harder to make the case for restoration and has slowed progress. The overall aim is to restore five million juvenile oysters while also establishing broodstock sanctuaries and improving areas of the seabed to encourage settlement. Despite these difficulties, the project has made significant progress since it began in 2016. So far, we have restored 25,000 oysters and seen some incredible results from our cages – 91% survival rates of the oysters and over 90 other species identified living around the cages, including critically endangered eels. We have also hosted school visits to the sites and BLUE is working to create a programme to engage volunteers in monthly monitoring. In early 2019 we hope to relay a million oysters onto the seabed.


Knowledge gaps

When comparing the results in the US with our ambitions it is crucial that we remember that the European flat oyster is a different species and therefore we need more research on its survival, growth and reproduction conditions to ensure that we tackle restoration in the right way.

We need better recognition from legislation of shifting baselines. This is best highlighted in the Solent where often we are found arguing for an oyster bed in an area designated for something less complex… like mud. There needs to be recognition that, if 15 million oysters were taken out in 1978, beds were extensive in the Solent and restoration should be using historical data to make the case!

We also need to carry out our own modelling of how much water a European oyster filters.

The problems of barriers such as disease, issues of density and seed supply also remains.


Next Steps

Restoration needs to be a national objective in the UK – only then will we be able to achieve meaningful restoration and take advantage of the ecosystem services oysters provide in the UK. Increased awareness and education is also needed to drive funding and engagement. The newly created UK Native Oyster Network and Native Oyster Restoration Alliance of Europe hope to work together linking all restoration initiatives, scientists, industry and government agencies to exchange knowledge and drive this forward.


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