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When European colonists arrived in southern Australia some 200 years ago, the coastlines were brimming with life. Expansive, kilometers-long reefs of angasi oysters—also known as Australian flat oysters—ringed the coast, teeming with fish of all forms and colors, bountiful crustaceans, and lush kelp forests. Yet, as they did on the east coast of North America, colonial fishers stripped the sea down to the studs. Today, except for one surviving Australian flat oyster reef in Tasmania, Australia, this once-abundant ecosystem has disappeared.

“It’s hard to imagine the scale of the reefs that were lost,” says Dominic McAfee, a marine ecologist at Australia’s University of Adelaide. Worse still, McAfee adds that “with the loss of those reefs, there was social amnesia that they ever existed. Very quickly, people forgot about them.”

Over the past decade, however, scientists have become reacquainted with the historical reach of Australian flat oyster reefs, which decorated about 7,000 kilometers of the country’s coastline from Perth to Sydney and down around Tasmania. Australian flat oysters—not to be confused with the far more common European flat oyster, commonly known as the native oyster—form gigantic reefs comprised of billions of individuals that can be found as deep as 40 meters. “They’re like the trees in a forest or the coral in a tropical sea,” McAfee says. Besides providing habitat and boosting biodiversity, oyster reefs are known to filter water and bolster fish production. 

On the back of this learning, scientists have been working to restore these lost ecosystems—an endeavor that got a major boost in 2020 when the nonprofit the Nature Conservancy Australia teamed up with the government of South Australia on an ambitious project to bring flat oyster reefs back to the coastline near Adelaide, one of the country’s biggest cities. That project, as McAfee and his team show in a recent study, has been a resounding success so far, with the restored reef now hosting even more Australian flat oysters than the last remaining natural reef in Tasmania. “It’s quite astonishing,” says McAfee.

According to Michael Sievers, a marine ecologist from Griffith University in Australia who was not involved in the study, coastal restoration projects are generally “a little bit hit-and-miss.” Many coastal ecosystems have suffered—and continue to suffer—under strong human pressures and are severely degraded. Without a concerted focus “on alleviating the initial causes of environmental degradation and habitat decline,” says Sievers, restoring coastal ecosystems to their former glory is difficult.

Case in point: while there were some surviving Australian flat oysters scattered in the Adelaide area before the restoration project kicked off, the seafloor in the region was generally too degraded for juvenile flat oysters to settle down, take hold, grow into adults, and begin forming a new reef.

To solve this problem, the Nature Conservancy Australia and the South Australian government used cranes and boats to drop 14 limestone boulders in the water off Adelaide’s Glenelg beach to create the hard substrate the oysters need to thrive. To attract more juvenile Australian flat oysters to the boulders, the researchers played natural sea sounds, such as those of healthy reefs, through underwater speakers to lure the little oysters in. “That was a massive success,” says McAfee. “We put them in, they found [the reef], and they settled on it very quickly.” In just two and a half years, fish, crabs, squid, and algae have all taken up residence, as well.

According to McAfee’s analysis, the diversity of invertebrates, such as blue swimmer crabs and southern reef squid, on the restored reef is around 60 percent of that found on a thriving reef.

“The project and the outcomes so far look very promising,” says Sievers. “The reef is recovering,” he says, adding that he’s interested in seeing how the reef will develop in the long term.

As these Australian flat oysters continue to build out the restored reef, McAfee and the other researchers expect to see even more species flock in. The ability of the reef to increase the availability of species important to recreational fishers is a key feature, McAfee says, which he sees as a way to make the ecosystem restoration project meaningful to Australian coastal communities.

Today, there are roughly 60 restoration projects aimed at rebuilding Australia’s lost shellfish reefs. Despite that, says McAfee, “we are just sort of scraping at the surface in terms of what was lost.”