After more than 100 years, oysters are back in Belfast Lough.
Underneath a pontoon where the river Lagan meets the lough, within sight of the Titanic visitor experience and the busy port of Belfast, hangs the oyster nursery. Snug in their protective cages, the native molluscs can grow and reproduce in safety here.
“When we lift up the cages, they’re covered in life,” says Dr Nick Baker Horne, marine conservation manager with Ulster Wildlife. “Lots of baby crabs, which is great fun as you lift the oysters out and have the crabs crawling all around.
“You have sometimes other oysters, sea squirts, tube worms, sometimes little fish, plenty of mussels growing on there, and you get to see, hands on, that these things are an ecosystem of their own.
“Just by growing and living and making that shell, they create this really fantastic habitat, and it gives you an idea of what it could be like if we had these large oyster reefs out in Belfast Lough once more.”
Native oysters – ostrea edulis – were once commonplace in Belfast Lough, but by 1903 over-extraction, which left the molluscs increasingly vulnerable to pollution and disease, had wiped out the population and the fishery closed.
The oysters were believed to be extinct in the lough until 2020, when researchers discovered 42 live oysters at six sites on the lough shore.
“That was the first sign,” says Baker Horne. “That’s where this project stemmed from. They were growing in the wild, so how could we help them?”
Cages were used to protect the all-important oyster larvae from predators; the plan was to grow the oyster population to the size where they could be released into the lough.
The oyster nursery in Belfast harbour was installed last December, the first in Northern Ireland to be situated in a commercial shipping channel.
This autumn, “the plan is to create a seabed deployment,” says Simon Gibson, marine environment and biodiversity officer at Belfast Harbour Commissioners.
This will involve “about 3,000-3,500 young, small oysters out on an old shell bed in the harbour estate, which is a really good base habitat for them, and the idea is that they will grow and create a natural reef there, and then any of the larvae being produced in the nursery will then have a place to settle, which would be the ideal conditions for them”.
Native oysters bring many benefits: they boost biodiversity and filter seawater, improving water quality and reducing pollution.
“The long-term vision is to have large populations of oysters back out in Belfast Lough,” says Baker Horne. “They could create huge habitats, real complex reefs, biogenic reefs, biological, living beings ... where thousands to millions of oysters could be together creating this really complex structure with so much biodiversity and so much abundance of life.
“You can imagine the small little fish hiding away amongst that oyster reef, protecting itself from predators, and that kind of symbiosis and that biodiversity it creates is just fantastic.
“That’s what we always have at the back of our minds when we’re measuring each oyster and getting covered in mud, we’re thinking of that big picture of large, native oyster reefs full of life and fish and fantastic clean, clean water.”
Native oysters are “ecosystem engineers” which are increasingly being viewed as a “nature conservation tool”, says Dr Jose M Fariñas-Franco, lecturer in the Department of Natural Resources and the Environment and principal investigator in the Marine and Freshwater Research Centre at the Atlantic Technological University, Galway.
He has worked on the east coast of Scotland – where native oysters had also disappeared – and describes a “shifting mentality” there and in other parts of Europe around the ecological benefits of native oysters. In Ireland, he says, “we need more awareness of oysters being more than food”.
Native oysters and the beds they create are internationally recognised as threatened and declining species and habitats. Fariñas-Franco is involved in a project to document the last Irish native oyster beds off the Connemara coast, to use them as reference habitats in restoration projects elsewhere, potentially including Belfast Lough.
“It’s a baseline for restoration, to know what an oyster reef should look like, because in lots of places in Europe, we don’t know,” he says. “We’re using the oyster beds in the west of Ireland as a benchmark to record what’s in there, and this information is sorely needed in areas where oysters are long gone, to have success in bringing back an established oyster population and with it these lost ecosystems.”
The hope is that the oysters will set an example for the future. “We primarily want to look at nature-based solutions to tackle issues within the harbour,” says Gibson. “Be it pollution, invasive species, carbon emissions, there’s always a natural solution.”
“What we’re trying to do is add more nature back out there, really grow nature, and that’s something that really does give you hope,” says Baker Horne. “It’s a really positive movement of restoring nature, rather than just trying to protect the last remnants of what we have.”
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