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South Australians are suddenly hearing a lot more about oyster reefs – from the government, in the news and in conversation, online and in person. This is not accidental.
His state is battling unprecedented and harmful algae blooms. The crisis has drawn attention to another, long-forgotten environmental disaster beneath the waves: the historic destruction of native shellfish reefs.
Reefs formed by native oysters, mussels and other aquatic mollusks covered more than 1,500 kilometers of the state’s coastline until 200 years ago. In fact, they extend well beyond the state border, being present from the southern Great Barrier Reef to Tasmania and in the sheltered waters of bays and estuaries around Perth.
These vast communities of bivalves, which feed by drawing water up over their gills, would have helped clean ocean bays and support a smorgasbord of marine life.
Their destruction by colonial dredge fisheries – to feed the growing colony and supply lime for construction – has made our contemporary beaches more vulnerable to phenomena such as this algal bloom. And their recovery is now a central part of South Australia’s algal bloom response.
reconstruction of rocks
South Australia’s $20.6 million plan aims to restore diverse marine ecosystems, with two approaches to restoring shellfish reefs.
The first is to create larger rocks from limestone boulders. These have been constructed over the past decade with some positive results. Four are built in Gulf St Vincent near Adelaide.
Boulder rocks provide hard, stable substrate for baby oysters to settle and grow. When constructed at the right time in early summer, when oyster hatches are plentiful and looking for a home, oyster larvae can settle on them and begin to grow. But these are big infrastructure projects – think cranes, barges and boulders – and so take years to plan and execute.
So as well as these larger reef builds, the public will have the chance to help build 25 smaller community-based reefs over the next three years. From Kangaroo Island to Eyre Peninsula, these reefs will use recycled shells collected from aquaculture farms, restaurants and homes using dedicated shell recycling bins. There will soon be a dedicated website for the project.
The donated shells will be cleaned, sterilized, and packed in biodegradable mesh bags and degradable cages to provide thousands of “reef units” after being exposed to sunlight for several months. Larger rocks can develop from these smaller units.
This combined approach – reefs and grassroots restoration on an industrial scale – reflects both the scale of the ecological problem and the appetite for public involvement.
What about algal blooms?
Once established, very little can be done to propagate algal blooms of this magnitude. The ecological grief and despair is palpable among coastal communities, feeling like powerless witnesses to the disaster. The sentence reads strangely – dangling modifier? DH So, naturally, the focus turns to recovery – what can be done to repair the damage?
This is where the oysters come from. They can’t stop this blooming. And their restoration is no silver bullet to addressing the many stresses facing the marine environment. But healthy ecosystems recover faster and are more resilient to future environmental shocks.
As for shellfish reefs, South Australia already has some impressive runs on the board. Over almost a decade we have undertaken some of the largest shellfish restoration work in the Southern Hemisphere. Millions of oysters have found a home on our existing reefs, providing filtration benefits and supporting diverse marine life.
And although algal blooms have destroyed many bivalve communities, native oysters have thankfully shown a level of resilience. During a dive last week we saw new baby oysters that had recently settled on the rocks, seeding their recovery.
Over the past decade we have built a scientific evidence base, practical knowledge and community enthusiasm for reef restoration that benefits wider marine ecosystems. This is why shellfish reefs feature so prominently in algal bloom response planning.
Where will these new rocks go?
We need time to identify the best sites for large boulder rocks. At the moment, the priority is to monitor the ecological impacts and resilience of ongoing algal blooms. But work has already started on community-based reef projects.
About the authors
Dominic McAfee is a postdoctoral researcher, Marine Ecology, and Sean Connell is Professor of Sustainable Marine Futures, Institute of Environment, at the University of Adelaide. This article is republished from Conversation Under Creative Commons license. read the original article,
These rocks will broaden our scientific understanding of how underwater animals and plants find them. Sites will be selected based on ecological knowledge and community interest in ongoing marine management.
There are many ways communities can participate. Community involvement and education are the cornerstone of the work, and individuals can recycle their oysters, scallops and mussel shells. The public can also volunteer time to join shell bagging and caging programs, and even get involved in building reefs. Over time, the community will have opportunities to help monitor and count the oysters and other organisms that have settled on the recycled shells.
The future is created by the past
The impact of this harmful algal bloom is real and ongoing. But in response, South Australians are rediscovering a forgotten marine ecosystem. Rebuilding shellfish reefs won’t fix this – but along with catchment management, seagrass restoration, fisheries management and better monitoring and climate action, it is a powerful tool.
With the help of communities, reefs that were once broken up, forgotten and functionally extinct can be restored. It will take time for these reefs to support clean waters and rich marine life. But these community initiatives can show people that we all have a role to play in taking care of the beach.