History lessons

The decline of European native oyster (Ostrea edulis) populations in England by 95% since the mid 19th Century, due to overfishing, disease, pollution, predators and loss of habitat, is well documented, as are the various attempts to reintroduce this species throughout the UK.

The benefits of growing oyster reefs are numerous, including their ability to sequester carbon, filter and clean seawater, increase local biodiversity and provide habitat and food for other marine species. Oyster reefs also act as a barrier to storms and prevent erosion.

The UK and Ireland Native Oyster Network, set up in 2017 by a community of academics, conservationists, oystermen and NGOs (non-governmental organisations) working to restore self-sustaining populations of native oysters, lists seven restoration projects on its website, along with 13 fisheries and production companies actively involved in growing native oysters around our coasts.

Projects, including the Dornoch Environmental Enhancement Project (DEEP) sponsored by Glenmorangie Distillery and the Solent Oyster Restoration Project are reporting initial success, but much work remains to be done to restore UK stocks to former levels. New developments in genetic selection, hatchery techniques, and a better understanding of the dynamics of oyster reefs do, however, offer hope for the future.

Mapping the past, securing the future

In England, the Environment Agency recently launched a new data layer tool, to help increase the native oyster population.

The tool has been developed by academics from the University of Exeter, University of Edinburgh, and the Europe-wide Native Oyster Restoration Alliance (NORA).

It comprises mapped datasets of primary and secondary written sources extracted from government, scientific, maritime and popular media accounts, which mention the use and presence of historic native oyster habitats and fisheries in England, the Channel Islands and the Isle of Man. The locations of exploitation are identified, together with descriptions of the extent of the habitat and timings of any decline.

The information is based on the website of ArcGIS, a geographical information service, and it will also be available through the Coastal Data Explorer, a public web mapping portal managed by the Catchment Based Approach initiative.

The data layer tool works alongside the Environment Agency’s Native Oyster Restoration Potential maps, which highlight areas where oyster restoration could be successful, and the UK & Ireland Native Oyster Network and Environment Agency’s European Native Oyster Habitat Restoration Handbook, which offers guidelines on restoring habitats.

Used together, the handbooks and data layer maps should prove to be invaluable in countering the huge loss in native oyster reefs seen over the last two centuries, by encouraging and supporting new restoration projects.

In particular, the tool will be beneficial for local authorities, community partnerships and environmental organisations, in helping them to make the case for native oyster restoration initiatives. Such projects are one of three focus areas of the Restoring Meadows, Marsh and Reef (ReMeMaRe) habitat restoration partnership project.

Environment Agency Estuary and Coast Planning Manager Roger Proudfoot says: “The release of the information on where native oyster reefs were once present represents another milestone in our drive for more estuary and coast habitat restoration. We hope this new information will lead to new opportunities for restoring what has been lost. We know that oyster restoration is possible, we just need more capacity to upscale the current efforts and we look forward to this new information inspiring more projects to restore this magnificent mollusc.”

Dr Ruth Thurstan, Project Lead and Senior Lecturer at the University of Exeter agrees that whereas oysters once formed an understated but important part of British marine ecosystems and their complex reef habitats were key to supporting other marine life, much of this was lost as oyster habitats declined.

“Our marine ecosystems today are fundamentally different, and this map of historical oyster fisheries is a step towards building the knowledge base required for successfully restoring this important species in our coastal waters,” Thurstan says.

Hatchery, Oyster Restoration Company

Hatchery playing a key role

The Oyster Restoration Company aims to be a major player in oyster seed production and is on a mission to supply up to 150 million native oysters per year.

“We are committed to supporting regional communities, increasing biodiversity and ensuring cleaner and better oceans for future generations,” Chief Commercial Officer Owain Wynn Jones told Fish Farmer at the recent Blue Food Innovation Summit in London.

As well as providing high quality seed for restoration projects and the table market, the Oyster Restoration Company also supplies seed to major offshore infrastructure projects such as windfarms, which operate with net zero or net positive biodiversity impact targets.

“These businesses need enterprises that can help them achieve their targets, and we are well positioned to reliably supply disease-free, resilient oysters to support their goals. We also help large corporates to develop large-scale oyster reefs, as this is an excellent way to meet CSR/ESG strategies,” Wynn Jones said.

A major biosecurity advantage for the hatchery is being situated in a designated Bonamia-free area and in 2021, CEO Dr Nik Sachlikidis, announced a substantial breakthrough with a new screening process for the parasitic Bonamia pathogen in native oysters.

The company worked with aquaculture genetics specialist Xelect on the project, which uses a highly sensitive DNA test to sample water from an oyster tank. The test identifies the presence or absence of Bonamia and does not require any oysters to leave the hatchery, nor to be destroyed post-testing.

“This innovation takes some amazing academic work and applies it to the commercial hatchery setting. Ultimately, this process allows us as a hatchery to manage our broodstock more effectively to control for Bonamia in seed production, and it is an enormous step forward in the production of disease-free native oyster seed,” Sachlikidis said.

The Oyster Restoration Company is also selectively breeding native oysters for accelerated growth, disease resistance and improved yields, to help farmers reduce their dependency on the Pacific oyster, Crassostrea gigas, now renamed Magallana gigas. This work is contributing to the development of an Oyster Arc of different geographical strains, in conjunction with Heriot-Watt University.