South Australians are being urged to feast on local oysters and then donate the shells to restore native reefs, which will filter ocean water and help fight harmful algal blooms.
The program will also involve lumps of limestone being sunk in the ocean, with a soundtrack of snapping shrimp playing on underwater speakers to lure baby oysters in.
Dr Dominic McAfee, a marine ecologist at the University of Adelaide, said before colonisation there were about 1,500km of oyster reefs along the SA coastline, but dredging had rendered them “broken, forgotten and functionally extinct”.
A single oyster filters about 100 litres of water a day, so reefs of them make a significant difference to water quality.
SA has been hit by a devastating toxic algal bloom, which has littered beaches with thousands of dead fish and marine animals, and has been likened to an underwater bushfire.
A Senate inquiry into the bloom recommended funding for “projects that deliver large-scale, long-term marine ecosystem restoration and resilience including meaningful reef restoration along the SA coastline”.
McAfee has been working with the government on its reef restoration plans.
He said the shell donation plan was a way for the public – many of whom have been suffering ecoanxiety amid the ongoing devastation of the algal bloom – to get involved and find agency and purpose.
“People can enjoy eating beautiful SA oysters then recycle those shells to provide this biodegradable, natural substrate, which is what oysters historically used to build reefs,” he said.
“[The reefs] were all dredged out 200 years ago. We removed the reefs, the substrate, so now we collect shells, make sure they’re clean and sterile, and we place them on the sea floor and try to get oysters to come and live on them.”
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The shells will be put in a biodegradable cage. As baby oysters settle on them, they produce a substance that cements the reefs together.
McAfee said his team has shown underwater speakers playing the sound of a healthy reef dramatically increases the number of oysters per metre.
Female oysters can release up to 3m microscopic spats – baby oysters – which then float out looking for a place to live.
A healthy reef habitat has “lots of nooks and crannies” where little animals such as snapping shrimp live, he said. His team built an eight-metre “oyster raceway” and played that crackling sound, and the spats were drawn to it.
The state’s climate, environment and water minister, Lucy Hood, said the government was funding the creation of 25 community reefs that would use donated shells and four large-scale limestone reefs.
Building up wild and native oyster reefs filters the water, creates healthy habitats, restores seagrasses and promotes biodiversity and increased fish stocks, she said.
“You can’t stop this algal bloom from happening but communities wanted to know how they can help,” she said.
“They have felt that deep sense of grief and sadness at the sheer loss of marine life and [the impact on their] pristine oceans going through this difficult and unprecedented time.
“So that’s why we launched a volunteer portal and people can look at all the ways they can give back – so they can eat a lot of oysters, mussels and scallops from SA, then we sunbake them [to dry them and sterilise them] and use them for community oyster reefs.”
Another project run with the fishing conservation charity OzFish will involve volunteers collecting seagrass seeds, which then get sewn into hessian bags and put on the ocean floor to restore the seagrass fields.
The projects are part of a joint state and federal summer plan to help the community and industry recover from the bloom, and for research and monitoring.
While it was initially thought the bloom was mostly composed of the Karenia mikimotoi species, which prefers warmer waters, testing has shown the dominant species is Karenia cristata, which prefers relatively cooler waters.
That has fuelled some hope the bloom will not worsen over the warmer months.
Hood said testing showed levels of chlorophyll-a (which indicates the concentration of algae) had reduced, and said she was “cautiously optimistic”.
People who wish to get involved in the restoration projects or donate shells can visit the government’s algal bloom response website.
