- In short: Tasmania is the latest site for a project rebuilding reef ecosystems around Australia, reseeding them with native oysters
- What's next?: Scientists hope healthy reefs will establish and attract a range of marine species, ensuring their survival into the future
Plunge beneath the waters of Georges Bay on Tasmania's east coast and there's a shellfish reef full of sea life.
The reefs were once a dominant feature of southern Australia's coastline but the one near the fishing port of St Helens is one of the only known natural shellfish reefs still in existence.
A team of scientists and reef builders has been reconstructing the critically-endangered underwater ecosystems at sites around the southern coast of Australia.
"It's estimated that the reef at Georges Bay might be only 1 per cent of the native oyster reef habitat that we had in southern Australia," said Tasmanian project manager Paul Armstrong.
"[It's] about 40 hectares of native angasi (oyster) reef and it's a really great reference … and we can aim to build more reefs like that."
Funded by the federal government and The Nature Conservancy, the project includes the restoration of native blue mussel reefs in WA and native oyster reefs in South Australia, Victoria and Tasmania, as well as Sydney Rock Oyster reefs in NSW and Queensland.
Each reef is built using tonnes of local rock.
Divers then scatter the reef base with millions of baby oysters or mussels from nearby shellfish hatcheries.
If all goes well, the shellfish grow and attach to the reef base and each other and create a living reef that attracts other sea life.
Oysters key to attracting other species
The project's last reefs under construction are in Tasmania in the Derwent River and the D'Entrecasteaux Channel.
"We've got two reefs in southern Tasmania, about 900 tonnes of rock each," Mr Armstrong said.
They are being seeded with native angasi oysters this week.
"Native oyster reef habitat is really productive, it encourages a lot of other species to come in to the reef as well," he added.
Thirteen reef locations with many reef sites have been built around southern Australia.
The program began in South Australia in 2000 and Anita Nedosyko has been involved since 2016.
"We're not just building this just purely to bring back something that was lost," she said.
"We're building this so that these reefs are healthy long into the future and that we can ensure that our kids are able to grow up and enjoy the marine environment just like we have."
Already the reefs built at the start of the project are showing positive results.
"We're seeing crabs and shrimps, and sponges, and forests of seaweed, then there are little critters starting to grow," she said.
"We're starting to see all of these bigger fish start to come to the reefs as well, like schools of squid … schools of whiting and in some of our reefs, we're even seeing thousands of juvenile snapper already."
Early settlers dredged reefs with chains
Native shellfish reefs were prolific in Australian waters until the 1800s.
Early fishery records show that European settlers mined them for fish and lime.
"When your European settlers arrived in Australia, they came with sophisticated fishing methods … they took rakes, and they chained and dredged all of these reefs," Ms Nedosyko said.
"They were harvesting the oysters using these rakes and what was left was an area that was devoid of life.
"They were like the southern version of a coral reef, but the living structure was an oyster rather than a coral reef."
Scientists hope rebuilding the reefs will mean these critically-endangered native shellfish reefs have dodged extinction.
