In a quiet corner of Dún Laoghaire harbour, a pioneering ecological experiment is unfolding. Suspended in 300 black baskets, 18,000 European flat oysters are being given a monumental task: to bring life back to waters that became an oyster graveyard more than two centuries ago.
The Oyster Graveyard Rises Again
David Lawlor, co-founder of the Green Ocean Foundation, recently inspected the first of the long lines of baskets. Peering inside, he found 60 oysters in each, their shells tightly closed, shielding the life within. "They look great," he beamed. His optimism was echoed all down the 100-metre line. These oysters, however, are not destined for the dinner plate. Their purpose is far grander: to reproduce and restore the lost oyster reefs of Dublin Bay.
This ambitious project bets that a species which thrived in Irish waters for millennia can do so again. The European flat oyster (Ostrea edulis) once formed sprawling reefs across the continent, but they were obliterated by a combination of overfishing, dredging, and pollution in the 1800s. Ireland's inhabitants cultivated them in the Middle Ages, but industrialisation sealed their fate in Dublin Bay.
Climate Heroes at Work
Why such effort for a humble shellfish? The answer lies in their extraordinary environmental prowess. "These oysters are amazing climate heroes," explains Lawlor. Each oyster is a natural filter feeder, processing up to 190 litres of seawater every day. By consuming plankton and nitrates, they clear algae, allowing sunlight to penetrate deeper. This boosts seagrass growth—a significant carbon sink—which in turn enhances coastal biodiversity and stabilises marine habitats.
Oyster reefs create rich ecosystems, providing a home for nearly 200 species of fish and crustaceans. They also play a vital role in nutrient cycling and shoreline stabilisation. The project in Dún Laoghaire is part of a wider European movement to revive these lost ecosystems, inspired by initiatives like New York's Billion Oyster Project.
A Careful, Step-by-Step Process
The Dublin initiative began with pilot projects, moving oysters from Tralee Bay in County Kerry to several sites ringing Dublin Bay, including Malahide, Howth, and Poolbeg. The oysters fared especially well in Dún Laoghaire, leading to the current phase. Last November, volunteers placed the 300 baskets in a sheltered part of the harbour.
The goal is for these adults to become broodstock, spawning baby oysters this summer that will settle on the harbour bed and, in time, form a new reef. Scientists from Dublin City University’s Water Institute have analysed the water for baseline indicators and will monitor the oysters' impact using sensors and biological assessments.
Maintenance is a hands-on affair. Every few weeks, volunteers like Andrew Collins and Aoibheann Boyle join Lawlor to flip the baskets by hand. This allows Arctic terns and gulls to peck away fouling organisms, ensuring water flows freely through the baskets. The project uses a different technique to one in Belfast Lough, where Ulster Wildlife recently placed oysters directly on the seabed.
"The temptation is to think massive, but you need to take one step at a time," says Lawlor, emphasising the importance of collaboration with government departments, local councils, and harbour authorities. While smaller than some European efforts, such as the Luna Oyster Project aiming to restore 4 million oysters to the North Sea, the Dublin team is focused on building a sustainable, community-supported model for marine restoration.
