Native oysters on the seabed

NatureScot’s position on engineering solutions to support marine habitat and species enhancement

https://www.nature.scot/doc/naturescots-position-engineering-solutions-support-marine-habitat-and-species-enhancement

June 2026

Summary

This paper articulates NatureScot’s current position on the use of engineering solutions to aid active restoration of habitats and species in the seas around Scotland. Whilst we appreciate that there is some overlap between restoration in the sea and restoration at our coasts (e.g. managed realignment), this position paper covers engineering solutions to support marine habitats and species only. Engineering solutions can include the introduction of man-made structures (e.g. concrete or other manufactured materials - ‘hard’ engineering) and natural materials (e.g. bivalve shells or trees etc. - ‘soft’ engineering).

This paper will be updated as needed, based on learning from projects using these solutions and new innovations.

Background

  • NatureScot provides advice on marine and coastal restoration projects. The Scottish Government’s Marine and Coastal Restoration Plan is expected to stimulate additional interest and funding for new projects looking to restore habitats and species at the coast out to 12 nautical miles, although the current focus is in shallow, nearshore waters.
  • As part of a gradual ‘scaling-up’ of marine restoration projects, to deliver more meaningful ecological outcomes and realise economies of scale, we are starting to see proposals that incorporate engineered solutions used successfully in other parts of the world.
  • Examples vary from use of natural materials such as sand and dredged material for seagrass restoration, or cultch (whole or crushed shell, possibly mixed with other substrata e.g. gravel) for native oyster restoration, to artificial structures such as biodegradable bricks and towers to aid restoration for native oysters and serpulid aggregations (for details see Examples of engineering solutions section below).
  • Restoration and enhancement activities are also being proposed to help mitigate environmental impacts associated with new developments. Examples include native oysters on offshore wind scour protection, and the use of ‘hanging shelters’ on harbour infrastructure to provide additional habitat and increase local biodiversity.

Principles

  • The priority should always be to conserve and protect Scotland’s marine environment, recognising that it is more ecologically beneficial and cost effective to look after existing features that are already providing ecosystem services and benefits, by reducing or removing pressures that may be impacting them.
  • NatureScot is supportive of projects seeking to restore and increase resilience in marine habitats and species.
  • Marine restoration activities need to take place in the right locations; those with environmental conditions suitable for the habitats and species of interest to establish and thrive, or areas which have been degraded by historic activities and have not re-established naturally but could be restored if pressures have been removed. Considering our changing environment and climate, such locations are unlikely to be constrained to those known to be suitable historically, but these may be a good place to start.
  • NatureScot is keen to see projects that work with nature and natural processes. As a general principle, we would prefer that projects minimise the introduction of man-made materials into the marine environment.
  • In locations that formerly supported target habitats and species and where the deterioration may be reversible, soft engineering solutions may be proposed to facilitate restoration, e.g. the addition of cultch into an estuarine system where shell and other hard substrates have been lost historically through extractive fishing activity.
  • We encourage early and proactive discussions to maximise the benefits of engineering solutions by considering the suitability of locations, biosecurity and design enhancements.
  • We will consider novel and potentially beneficial proposals on their merits. We recognise that there is a need to trial different methodologies and approaches to inform our position, and that research is ongoing regarding the biodiversity benefits associated with artificial structures.
  • We do not support the use of engineering solutions to alter existing, non-degraded natural habitats into an alternate state considered more suitable for restoration, e.g. sand capping of shallow sea loch mud habitats for seagrass restoration in an area unlikely to have ever supported seagrass.
  • Similarly, we do not currently support substantive hard engineering works being used with the explicit intention of permanently changing physical conditions to make an area more suitable for restoration activity. As above, this would alter an existing natural habitat for the purpose of restoring a different habitat, which would not otherwise have been feasible in that location.

Specific factors we will consider when developing our advice on a proposal that contains engineering solutions

  • The scale and location of any proposed engineering solutions and the anticipated effects on the receiving environment, beyond the intended restoration outcomes.
  • Whether the engineering solutions are proposed specifically to support habitat / species restoration or whether this activity is ‘opportunistic’, looking to capitalise on anticipated changes in the environment arising from existing, approved works (potential linkages to mitigation, compensation and Nature Inclusive Design (NID) - see section below).
  • The ‘natural’ state of the location where restoration activities are proposed - the current biological and physical conditions (or those that might reasonably be expected if pressures were removed or might have been present historically) in terms of the suitability for the target habitat or species, including factors such as predominant sediment types, wave exposure, currents, salinity, etc.
  • The origins and ‘environmental costs’ of introduced materials (concrete, plastics, hydrocarbons - energy demands and carbon emissions in the production and siting - applicable to both man-made and natural). For natural products, consideration will be given to the likelihood of these being found and at what scale, at the receiving location. Impacts associated with removal from their source location will also be a consideration.
  • The likely fate of any introduced materials, including but not limited to: decay, associated emissions and leaching of contaminants, potential for biofouling and provision of substrates for the spread of marine INNS, longevity, whether practicable to remove if needed, how decay/removal may impact the ‘restored’ habitat/species, how these introduced materials will be monitored and maintained over time.
  • Wider environmental considerations, based on the area concerned and the most up to date research on potential interactions, for instance use of the area by other species (such as waders and waterfowl).
  • Biosecurity considerations, including known geographical presence of marine INNS, particularly those such as Didemnum vexillum and Crepidula fornicata which are known to attach to substrate. Further biosecurity guidance can be found in NatureScot Commissioned Report 748: Marine Biosecurity planning - identification of best practice: a review.

Additional considerations

  • NatureScot has a statutory advisory role in considering proposals for enhancement within, or with connectivity to, Protected Areas. Any such proposals would need to be considered against the Conservation Objectives and protected feature sensitivities of the designated site(s). We are also in the process of developing a position paper on marine restoration within the MPA Network.  Likewise, proposals likely to impact Scotland’s Priority Marine Features (PMFs) will also be assessed as per National Marine Plan (NMP) Policy, GEN 9.
  • We recognise that there is an evolving policy landscape with regards to the forthcoming National Marine Plan 2 (NMP2) and other policy developments, and we have a commitment to review and revise this paper where required.
  • This position paper is consistent with our advice to draft policy proposals set out in our response to the NMP2 Planning Position Statement around Nature Inclusive Design (NID), Nature Positive development and compensatory measures. We support the inclusion of consideration of nature through infrastructure design, supply chain, and development lifespan in NMP2 and will continue to feed into the development process.
  • Biosecurity is a key consideration when we advise on engineering solutions to support marine restoration, with the newly published Scottish Action Plan for Invasive Non-Native Species (INNS) recognising the need to prevent, detect early and respond rapidly to INNS incursions in Scotland.
  • The newly published Shetland Islands Regional Marine Plan and the Orkney Islands Marine Regional Plan include restoration considerations - see specific guidance on marine restoration in the Shetland Isles: Guiding Marine Restoration and Enhancement in the Shetland Isles, alongside specific marine INNS considerations (see policy MP INNS1 in the Shetland plan and General Policy 13 in the Orkney plan).
  • We recognise that under National Planning Framework 4 Policy 3(a) and 3(d), aquaculture development proposals must contribute to enhancement of biodiversity, with guidance currently under development by Scottish Government.

Examples of engineering solutions

Recent examples of engineering solutions which are currently underway or have been proposed, both in the UK and abroad, to support marine habitat and species restoration include:

  • ‘Sand-capping’, where a modest layer of sand (typically 10 cm thick) is applied to the seabed to create a stable surface suitable for seagrass planting and to modify anoxic areas of sediment where the seeds would not germinate. A trial in Scotland has explored the incorporation of seagrass seeds into the sandy sediments to kickstart the process, but this was not successful, likely due to high water turbidity and low seabed light levels.
  • In Scotland in 2025, native oyster restoration projects sought to deploy increasingly sizeable volumes of ‘cultch’, a mix of crushed shell material and gravel, to provide hard substrates for oyster spat settlement.
  • In Scotland there is interest in adding nutrients to the seabed within seagrass meadows to enhance seed production, through burying a hessian bag with nutrients into the sediment.
  • Use of trees to simulate decaying wood habitats in shallow seas, that are now naturally depleted because of the loss of woodland habitats on land, for aiding restoration of invertebrates (including native oysters and mussels), and fish communities. There is positive research from Germany and the Netherlands with regards to biodiversity, but this has yet to be trialled in Scotland.
  • Beneficial use of dredged material for marine habitat restoration, such as seagrass seeding or to create suitable substrate for shellfish restoration (at the current time dredged material is primarily used for estuarine and coastal restoration in the UK, such as for saltmarsh habitat enhancement and managed realignment which are not covered by this paper).
  • The LIFE-funded Ecorest project has used epoxy putty to attach cold water corals back onto rock substrate and deployed the corals back to deep sea off Catalonia. In Scotland, deep-sea corals have been translocated from decommissioned oil platforms to a site off Shetland’s west coast, using purpose-built artificial reef units.
  • Artificial Seagrass (ASG) mats have been trialled in the lab for use in high energy areas where other natural protection mechanisms are unsuitable.
  • Deploying biodegradable bricks or towers onto soft sediments to aid native oyster restoration. ReefCircular towers have been trialled on the west coast of Scotland, without success to date. However, there are a number of companies producing a range of these types of products, some of which have been trialled abroad, including Reef Balls, Oyster Heaven’s “Mother Reef” bricks (see research article here), and Resting Reef's ashes-mix memorial structures.
  • Non-biodegradable Oyster Reef Cubes with native oysters attached have been deployed off the north-east English coast.
  • Native oyster restoration on scour protection in wind farms. This is currently being undertaken in the Netherlands, but there is interest in pursuing this in the UK.
  • Artificial reefs have been installed in seagrass beds in the Caribbean to promote ecosystem services in both human disturbed and undisturbed meadows.
  • Artificial Seagrass Sheilds (ASSs) have been trialled off the coast of the Canary Islands to facilitate C. nodosa seedling transplants.
  • The use of ‘hanging shelters’ on harbour infrastructure to provide additional habitat and increase local biodiversity.
  • Action West Loch, based in Argyll, received funding in 2025 for the deployment of ceramic reef structures to encourage larval settlement for growth of serpulid worms.
  • Deployment of Blusinkies - pebble-sized artificial substrates which benthic organisms attach to. These have been tested abroad, for instance in Madeira, and there is interest in trialling them in Scottish waters.