Aquaculture for all

Native oyster reintroduction set to double biodiversity

Water quality Blue carbon Oysters +6 more

Project to reintroduce European native oysters unveils first predicted impact of species’ return and aims to improve water quality, enhance marine biodiversity and increase carbon storage in the Dornoch Firth over the next decade.

Three men in a boat
Professor Bill Sanderson, Heriot-Watt University, Calum Duncan, Marine Conservation Society, and Hamish Torrie, The Glenmorangie Company

Key participants in the DEEP project at Loch Ryan. © Charné Hawkes

New research from Heriot-Watt University in partnership with The Glenmorangie Distillery and the Marine Conservation Society has, for the first time, predicted the biodiversity gain of reintroducing European native oysters (Ostrea edulis).

The innovative Dornoch Environmental Enhancement Project (DEEP), first initiated in 2014, seeks to reintroduce four million oysters by 2030 into the protected area of the Dornoch Firth on the banks of Glenmorangie Distillery in the Highlands of Scotland, UK. The species had become extinct, probably due to overfishing, over 100 years ago.

Oyster restoration efforts are growing across Europe as more is understood about the ‘ecosystem services’ provided by reefs which include a range of benefits to people and the environment. But with intact oyster reef habitats so rare, researchers have had limited data to work with to help predict the biodiversity benefits of this marine conservation work - until now.

Writing in peer-reviewed scientific journal PLOS ONE, Heriot-Watt researchers studied the biodiversity of Scotland’s last remaining native oyster fishery at Loch Ryan in south-west Scotland. The fishery has operated since 1701 and uses a rotational harvest system where different areas are fished each year and then left to repopulate for six years before they are fished again.

As well as giving the researchers a window into the past, studying Loch Ryan has allowed the team to predict what a future reef in the Dornoch Firth could look like once oysters are fully restored. This was achieved by studying the effect of oyster reef development and biodiversity gain at different stages after the oyster habitat had been fished.

As lead author Naomi Kennon from Heriot-Watt University explains in a press release: “The findings from our research in Loch Ryan are extremely exciting, demonstrating that biodiversity will likely double over a decade once oyster restoration projects are complete. This means the population of species will increase in a balanced way. Our data has also shown a link between increased shell material as the oyster population grows and increased biodiversity.”

A short film explaining the research © DEEP

In the study, three treatments were surveyed for faunal biodiversity, oyster shell density and oyster shell percentage cover. These treatments were plots that had been harvested one year, two years, and six years before the study began. The treatments were surveyed with SCUBA using a combination of video transects and photo quadrats. Modelling was used to predict changes in the Shannon-Wiener's Diversity index (a globally recognised and popular measure of diversity) over time since fishing.

Calum Duncan, head of Conservation Scotland at the Marine Conservation Society said: “The study in Loch Ryan shows that increasing the complexity of the seabed allows many species to find refuge in this living reef. We therefore look forward to thousands more native oysters being released in the Dornoch Firth, to attract even more biodiversity to the area.”

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