Restoring Shellfish Reefs

Shellfish Reefs are just as important as Coral Reefs, and a project is aiming to reverse their decline

Shellfish reefs have the unenviable distinction of being the most critically endangered marine ecosystem on the planet. Globally, they are disappearing at a rate greater than the losses reported for coral reefs, mangroves and seagrasses. In Australia, shellfish reefs once thrived in bays and estuaries from Noosa in Queensland around the southern coastline to Perth in Western Australia. Today, as a result of overharvesting, dredging, disease and pollution, less than 10 per cent of these vital habitats remain and are considered 'functionally extinct' in many locations. 

However, one conservation organisation — The Nature Conservancy (TNC) — is taking action to reverse this decline. TNC is a non-profit, non-government organisation dedicated to environmental conservation in 72 countries across six continents, including Australia. Founded in the United States in 1951, it now comprises more than a million members and 600 scientists world-wide. In Australia, TNC works closely with business, government and local communities on a range of conservation projects, including several aimed at restoring our endangered shellfish ecosystems. 

Shellfish reefs are complex structures, composed of millions of oysters and mussels, that provide food, shelter and protection for a diverse range of marine plants, fish and invertebrates (shrimps and crabs). They grow in size and mass by accumulating dead shell material and mainly occur in intertidal zones of bays, estuaries and nearshore coastal waters where they filter water (one adult oyster can filter up to a bathtub of water a day), stabilise sediment and provide an important natural defence against erosion and storm damage to fragile shorelines. The reefs also provide important social and economic benefits to coastal communities through recreational fishing and diving, aquaculture and ecotourism.

Reef construction begins with the careful selection of a suitable site using a combination of science, field survey and detailed consultation with local stakeholders. Next, the reef base is created by laying natural materials on the seafloor, often a combination of limestone rubble and recycled shells from oysters, mussels and scallops, which mimic the foundations of a natural reef. The recycled seafood shells are collected from local restaurants as part of the ‘Shuck Don’t Chuck’ shell recycling project, which utilises thousands of tonnes of material that would otherwise end up as waste in landfill. Once completed, the new reef structures are seeded with millions of baby oysters and mussels grown in nearby hatcheries. These shellfish grow and attach to the reef base and each other, creating a living reef which further attracts fish and other marine life.

Scientists monitor the reefs for several years after construction for threats, such as predators and disease, and may adjust the structures to ensure they grow and thrive as a natural, self-sustaining environment. 

This innovative project is revitalising reefs from Western Australia to Queensland in partnership with a wide range of organisations — recreational and commercial fishers, diving and fishing clubs, oyster and mussel growers, seafood wholesalers and restaurants, maritime engineers and construction companies, natural resource managers, local communities, schools and Traditional Owners — creating an estimated 850 jobs in associated sectors. Seven restoration projects are already underway or near completion, with a number of others expected to begin within the next two years.

The construction of a new shellfish reef within Oyster Harbour near Albany, WA, began in November 2019 with the placement of over a thousand tonnes of local limestone onto selected sites. This phase will initially cover more than 800 square metres by July 2020, with future enlargement planned to between five and ten hectares. 

Another project flagged for Western Australia is the restoration of shellfish reefs in the Swan-Canning Estuary in the heart of Perth. Once completed, the project will enhance the quality of water in this important wetland ecosystem that supports significant populations of fish, dolphins and birdlife.

The new Windara Reef in Gulf St Vincent, SA, comprises 150 smaller reefs spread across 20 hectares of seafloor about a kilometre offshore from Ardrossan on the Yorke Peninsula. The project was completed at a cost of $4.2 million in November 2019 with the placement of seven million hatchery-raised native oysters and is the largest restored shellfish reef in the Southern Hemisphere. TNC, in partnership with the South Australian Government, now aims to build the state’s second shellfish reef in Adelaide’s metropolitan waters in Gulf St Vincent. The Port River Shellfish Restoration will be at least 1,500 square metres spread over two hectares and is expected to be completed by late 2020. 

In Port Phillip Bay, VIC, TNC has restored up to 20 hectares of shellfish reefs at two main locations — Margaret’s Reef in Hobsons Bay, off St Kilda, and Wilson Spit Reef at Geelong — and plans to reinstate a further 500 hectares of lost reefs (equivalent to 700 soccer pitches) around the Victorian coastline.

TNC, Noosa Shire Council and the Australian Marine Conservation Society are working together to rebuild functionally extinct oyster reefs in the Noosa River, Qld, and increase local stocks of snapper, bream and mullet, thereby enhancing Noosa’s reputation for nature-based tourism and outdoor living. Similar projects are planned for the restoration of historic shellfish reefs in the Pumicestone Passage, near Bribie Island.

In New South Wales, TNC is engaged in a number of projects to improve critical shoreline ecosystems in Sydney Harbour, Brisbane Water (Gosford), the Hastings River (Port Macquarie) and the Macleay River (South West Rocks). Its OceanWatch Living Shoreline Program won the Innovation Award at the 2018 NSW Coastal Conference and was a finalist for a Green Globe Award.

The Nature Conservancy Australia

Suite 2.01, 60 Leicester Street, Carlton, Victoria

P: (03) 8346-8600

E: australia@tnc.org

W: www.natureaustralia.org.au

For information about the Australian Shellfish Reef Restoration Network email: coastalrestorationnetwork@gmail.com.