The UK has the largest installed capacity of offshore wind in the world. With a government commitment to further expand, opportunities for co-location with conservation and restoration initiatives are being increasingly explored. Globally, over 85% of oyster beds have been lost, making them among the most imperilled marine habitats in the world. In the UK, the native oyster, or European flat oyster, has declined by 95% since the mid-1800s. Oyster restoration is a high priority at the national and European level with several pilot projects underway in Europe to investigate the potential for offshore wind farms to aid population recovery. The use of broodstock sites to increase larval supply is considered an effective strategy to restore self-sustaining populations. Restoration projects including the Solent Oyster Restoration Project led by Blue Marine Foundation (BLUE) have successfully used marinas as broodstock sites, pumping billions of larvae into the Solent. Results from a pilot in The Netherlands identified larvae in oysters housed within a North Sea wind farm and the surrounding water, showing oysters can grow and reproduce in these offshore environments.
This report provides a summary of work undertaken by BLUE and renewable energy company Ørsted, in collaboration with the Essex Native Oyster Restoration Initiative (ENORI) and includes results from a feasibility study by Resilient Coasts. The project explored the potential for the Gunfleet Sands wind farm in Essex to act as a broodstock site for the Blackwater, Crouch, Roach and Colne Estuaries Marine Conservation Zone (MCZ). The MCZ is the only designation for native oyster beds in the UK and ENORI is leading efforts to restore populations to a self-sustaining level. The feasibility study assessed the physical processes at the wind farm and how these would impact oyster survivability. Key considerations included: environmental tolerances for native oyster survival; combined hydrodynamics (waves and tides); operational requirements and the design of oyster housing. The results indicated that a spawning event, combined with a flood tide, may allow larvae to reach the MCZ under specific weather conditions. However, the perfect window of opportunity for larval transport is relatively small and unlikely to coincide with larval release. The study also concluded that, for this location, oysters should not be placed on the seabed either in untethered cages or loose because of the high energy within the site. Depth, bed sediment and infrastructure constraints further reduced the area available for broodstock installations within Gunfleet Sands. This raised concern over the potential to scale up broodstock numbers and the overall impact of the project, as well as financial investment. It was therefore decided that a pilot phase would not be developed.
The findings from this study have formed the foundation of a wider scoping analysis of over fifty UK wind farms, using broad-scale seabed habitat and energy level data. Initial results from the scoping study has presented several sites that may be suitable for restoration and habitat enhancement for native oysters. BLUE is now extending the scoping to other species and habitat enhancement opportunities, with the aim of initiating a new feasibility study in 2021.