Native Oyster Restoration

Exploring the feasibility of marine habitat restoration in the Scottish Highlands

Project information

The European flat oyster (Ostrea edulis) is a native mollusc that has been a common feature of Scotland’s coastlines for millennia. Otherwise known as the native oyster, they form living reefs that provide shelter and breeding grounds for a range of underwater species. A single adult oyster can filter up to 240 litres of water per day helping light-reliant species such as seagrasses. Due to a range of threats, native oysters in the wider UK have experienced a dramatic decline of 95% since the mid nineteenth century. This once widespread species (coined as 'the poor man's food') now exists in small, isolated populations. This project sets out to explore the feasibility of restoring this important species. The first stage involves conducting species and habitat surveys in collaboration with Moray Ocean Community. In conjunction with this, there will be native oyster survival trials conducted in the project area to see whether they can still thrive there.

A Species of Cultural & Ecological Significance

Densities of the native oyster were once so great that they formed large reefs along Europe’s coastlines. In Scotland, this common bivalve mollusc would have been an integral part of people’s diet. During the 18th century, it was estimated that the oyster reef at the Firth of Forth would produce around 30 millions oysters per year! As an important source of food, oysters were cultivated and fished for thousands of years with records going back to Roman times.

More than just being culturally significant, native oysters can be ecologically valuable when they exist in healthy numbers. Forming living ‚Äėbiogenic‚Äô reefs, they provide food and shelter for other marine wildlife. Crevices in the reef make ideal spaces for other organisms such as fish to seek shelter and reproduce. Native oysters also act as biofilters helping to improve water clarity. They filter particles from the water column which assists important light-dependent species like seagrasses. In turn, seagrasses provide ecosystem services such as oxygen production and nutrient cycling. Furthermore, where native oyster populations bounce back, there could be a positive impact on local fisheries. As a habitat for fish and the species they feed on, oyster reefs are capable of creating a ‚Äėspill-over‚Äô effect that could see local economies and livelihoods benefit.

A close up shot of a European flat oyster
Known as 'oisir/eisir' in Scottish Gaelic, native oysters and native oyster beds are a "Species and Feature of Conservation Importance‚ÄĚ under the Marine and Coastal Access Act.

The Struggle for Survival

Today the situation is drastically different from the bountiful populations of the past. They are one of the most threatened marine habitats in Europe. From being present around most of the UK’s coastlines, the species is now considered to be on the brink of extinction, only existing in small, fragmented populations. The threats attributed to this collapse in Scotland are overexploitation for fisheries, pollution/poor water quality (particularly tributyl tin which has been found to stunt growth), parasites, diseases and historic habitat loss. Native oysters require a substrate for their young to attach to and the loss of oyster beds has therefore impacted their decline.

As populations become smaller, their ability to survive is hindered by their very own nature. Instead of using broadcast spawning to reproduce, where eggs and sperm are released into the water at once, female native oysters first draw sperm into their bodies before releasing fertilised eggs. This means where there are fewer oysters together, there is less success of fertilised eggs spreading. Being protandrous hermaphrodites, animals that are born as males but switch sexes during their life cycles, is also known to affect reproductive rates. Skewed sex ratios in favour of males has been reported and is possibly due to stress related to disease and/or anthropogenic pollutants. In addition to these factors, native oyster larvae need a surface to attach to and their favourite is the shells of older native oysters. Lower densities of native oysters mean that there are fewer places for their larvae to latch on to and grow. 

Although not included on the IUCN database, the European native oyster features on the OSPAR List of Threatened and/or Declining Species and Habitats. It is also part of NatureScot‚Äôs Species Action Framework, in addition to appearing on the UK Biodiversity Plan Priority List and the Scottish Biodiversity List. In terms of legislation, native oysters and native oyster beds are a ‚ÄúSpecies and Feature of Conservation Importance‚ÄĚ respectively (SOCI and FOCI) under the Marine and Coastal Access Act.

A close up shot of a European flat oyster in a person's hand.
Native oysters are a species of high conservation priority in Scotland.

Our Project

In partnership with the Moray Ocean Community (MOC), we are investigating the feasibility of native oyster restoration in the Cromarty, Inverness and Beauly Firths. To begin with, we are conducting community-led intertidal surveys and professional subtidal surveys that aim to gather baseline data on:

  • the presence or absence of oysters in the survey areas;
  • habitat mapping and species distribution to inform future marine restoration projects;
  • the presence of other important species to ensure that any restoration efforts do not negatively impact them, mainly seagrasses (a Priority Marine Feature in Scotland, as are native oysters).¬†

Community-led intertidal surveys

These surveys will be carried out following guidance from NatureScot’s Community-led Marine Biodiversity Monitoring Handbook. Using the help of community volunteers, the methods include using species image library (SIL), underwater marine life observation (MLO) and feature focus: habitat mapping (HM). Project staff from Mossy Earth and volunteers from MOC  will be trained as BSAC Shore Surveyors and Seasearch Observers to learn about the species and habitats we might encounter. Anthropogenic pressures on the foreshore will also be recorded (such as waste water outflows). 

Subtidal Surveys

The objective of these surveys is to identify and record live wild native oysters/oyster beds (if they still exist within the project area), dead native oyster shells and seagrasses. This will be done in transects using a DTG3 remotely operated vehicle (ROV) equipped with an inertia navigation system. The vehicle is able to travel in straight lines capturing high quality video footage for analysis. The video data generated by these surveys will be stored in an online database, with a view to offering the footage to expert benthic taxonomists to identify and record other marine life where possible.

Although European flat oysters are the main focus of this project, data on other marine species will also be collected. This includes the two species of seagrass present in the project area: eelgrass, dwarf eelgrass and their beds. If seagrass meadows are detected, further in-depth surveys will be undertaken in accordance with Seagrass-Watch standards. The objective is to demonstrate that any restoration works will not negatively impact other important species. 

The results of the surveys will help inform native oyster restoration in the area and which methods would be most suitable. Furthermore, the findings will also provide data for potential seagrass restoration projects.

Strict biosecurity protocols will be in place when managing all equipment to reduce the risk presented by invasive non-native species and parasites to the marine environment, with all staff and volunteers made aware of the potential risks these pose to the marine environment. Check, clean, dry!

To date, Mossy Earth has funded the set up costs of the surveys which include staff costs, equipment and training fees.

Stakeholder Engagement 

Community involvement is a key component of this project. From the early stages, partnerships have been developed with local communities and shellfish farmers. Through direct participation in the surveys, we hope to help foster people's connection with the marine environment. This engagement should also garner support for the project and contribute to the long-term sustainability of native oyster restoration in the area. We will also work to establish wider community support by reaching out to local schools and community groups.

We are exploring the possibility of collaborating with an academic institution to monitor the project’s outcomes. This could consist of eDNA, acoustic habitat mapping, bathymetric surveys, benthic taxonomy and acoustic biodiversity monitoring.

Andrew from Moray Ocean Community and Isla from Mossy Earth on a boat
Getting the support of the community 'onboard' is an important element of this project.

Evidence Sharing

Currently, there is a knowledge gap on native oysters in the project’s area. We intend to help address this by gathering data on species presence/absence, habitat mapping and distribution. We will submit our findings, such as species records, to online platforms like the National Biodiversity Plan Atlas and iRecord and DASSH. In addition, we will share our findings directly with Scotland’s nature agency, NatureScot. Video footage generated will be stored on an online platform and shared for analysis by benthic taxonomists if found to be relevant. The findings of the project will ultimately be used to facilitate active marine restoration.

We thank Mossy Earth members and everyone else involved in the effort to turn the tide for this important species.

a salinity probe on a boat out to sea
Through data collection, we aim to contribute to the knowledge of native oyster restoration in the area.

Stay tuned for updates...

At present, we are planning the surveys in collaboration with MOC and will provide further updates as the project progresses. See the video below where project manager, Isla, discusses the project in more detail.

The Moray Ocean Community logo