Before European settlement, shellfish reefs lined Australia’s coasts and estuaries, providing providing food for Indigenous people, supporting marine life and providing an array of environmental benefits, such as shoreline protection, carbon storage, water filtration and nutrient absorption. Today, less than 10% of these reefs remain.

There are a range of programs that are now restoring oyster reefs around the coast in efforts to recreate the vital ecosystem services these can provide, Below are just some examples.

Oyster reefs consist of colonies of living oysters and old shell. They occur in the intertidal zone or permanently submerged underwater.

Natural recovery of oyster reefs is limited by a lack of suitable hard material for oyster larvae (called 'spat') to settle. Reef restoration involves reintroducing material such as rock or sterile shells to the estuary floor, preferably in areas with high settlement rates of wild oyster larvae. Where settlement rates are low, spat produced in a hatchery can be settled onto the rock or shell.

One of the most ambitious efforts to restore oyster reefs in Australia is led by The Nature Conservancy. Their Reef Builder program set up several locations for large-scale marine habitat restoration.

The Nature Conservancy (TNC) shellfish reef building program is Australia’s largest marine habitat restoration initiative. It aims to rebuild 60 shellfish reef ecosystems across Australia by 2030, representing one-third of the geographic locations where this habitat once existed.

TNC’s Reef Builder project, a $20 million partnership with the Australian Government, sought to restore near-extinct shellfish reefs across southern Australia. Timing was also important: it provided economic stimulus to regional and metropolitan economies impacted by the COVID-19 pandemic.

Reef Builder was delivered between 2021 and 2023 in collaboration with government, natural resource management organisations, industry, First Nations groups, community groups, recreational fishers and universities. It has restored more than 40 ha of shellfish reefs across 13 projects in Western Australia, South Australia, Victoria, Tasmania, New South Wales and Queensland. These include Port Phillip Bay in Victoria, Windara in South Australia’s St Vincent Gulf, Oyster Harbour in Albany, Western Australia; and the Noosa River in Queensland.

The projects have shown that shellfish reefs can be restored at scale and their social, economic and ecological benefits returned to coastal communities. The following are examples of projects that have received support from the Reef Builder initiative.

In New South Wales, targeted restoration efforts are underway through the Marine Estate Management Strategy, focusing on improving water quality and biodiversity in key estuaries.

The NSW Marine Estate Management Strategy (MEMS) is leading a project to restore and research natural oyster reefs with the aims of improving water quality, aquatic habitat and biodiversity.

The project includes reef restoration at Port Stephens, Narooma and Kamay/Botany Bay; as well as mapping existing oyster reefs to identify other areas that could be restored.

At Port Stephens, DPI Fisheries worked with a local contractor to construct two oyster reef bases in the Port Stephens estuary using more than 3000 tonnes of rock and recycled oyster shell. The sites were carefully selected to minimise impacts on boating routes, recognize Marine Park zoning, maintain private foreshore access and preserve existing oyster reef.

The new reefs are located in places with suitable biological conditions for oyster settlement and growth. All the oyster shell was collected from local oyster farmers, to ensure no diseases were introduced from other estuaries. The construction workers placed the 75-300mm pieces of rock and oyster shell in the intertidal zone at two sites in 20-40 cm deep beds.

Construction work was timed to coincide with the highest levels of oyster settlement. In the first three years, 34 million oysters naturally recruited and established on the reefs and are filtering more than nine million litres (more than 3.5 Olympic-sized swimming pools) of water per hour. Twice as many bream were recorded at the new reefs compared to natural reef habitat and 35 fish species recorded, which is equal to that seen at natural reefs. As well, the new reefs are now providing habitat for smaller cryptic species.

Studies of the project area were conducted before the restoration to establish a baseline of information, including:

• sediment and reef core samples to identify marine life
• underwater video of fish communities
• environmental DNA analysis to determine species using the area.

As well as the above, monitoring after the restoration will record oyster settlement rates, oyster pests and disease, and water filtration rates by the oysters.

Wagonga Inlet is a stunning estuary which frames the popular holiday town of Narooma on the NSW south coast.

The Wagonga Inlet living shoreline project is a landmark initiative that demonstrates the importance of nature-based solutions to coastal erosion.

The project has created more than 1700 m² of intertidal Sydney Rock Oyster (Saccostrea glomerata) reef habitat using locally quarried rock on the sand flats. This habitat, which is exposed during low tide and submerged during high tide, is attracting wild oyster spat and, after two years, more than one million baby oysters have established there. As well as improving water quality and fish production, the reef will provide a natural defence against coastal erosion and damage from storms.

Next to the sandflats, is an area known as ‘Deep Hole’, where another 1000 m² of subtidal native flat oyster (Ostrea angasi) reef habitat is being restored on the sea floor. This subtidal reef, which remains underwater even at low tide, was hand seeded with two million young oysters settled onto clean recycled local oyster shell.

Combining commercial and native species

It is the first restoration effort to combine Sydney rock oysters and native Angasi oysters at a single location. After 2.5 years, the native flat oyster reefs are supporting the same number of fish species as remnant reefs.

As well as the new reefs, foreshore and saltmarsh areas have been rehabilitated to create a living shoreline, complemented by infrastructure including a boardwalk, access paths, jetty and swimming pontoon.

The project has restored critical habitats, supporting fish species such as luderick and bream and is also trialling the use of terracotta pipes into the subtidal reef as habitat and shelter for juvenile Black Rock Cod.

Indigenous involvement was critical in planning and implementing the project, particularly with input of local Aboriginal artists Nigel Stewart and Natalie Bateman.

Citizen science volunteers have recorded numerous shorebird species, including endangered pied oystercatchers and migratory waders, such as bar-tailed godwits using the intertidal reefs as high tide roosts when the surrounding sandflats are underwater.

The project is supported by Eurobodalla Shire Council, the NSW Marine Estate Management Strategy (MEMS); and TNC and the Australian Government through the Reef Builder initiative.

It is the first restoration effort to combine Sydney rock oysters and native Angasi oysters at a single location. After 2.5 years, the native flat oyster reefs are supporting the same number of fish species as remnant reefs.

As well as the new reefs, foreshore and saltmarsh areas have been rehabilitated to create a living shoreline, complemented by infrastructure including a boardwalk, access paths, jetty and swimming pontoon.

The project has restored critical habitats, supporting fish species such as luderick and bream and is also trialling the use of terracotta pipes into the subtidal reef as habitat and shelter for juvenile Black Rock Cod.

Citizen science volunteers have recorded numerous shorebird species, including endangered pied oystercatchers and migratory waders, such as bar-tailed godwits using the intertidal reefs as high tide roosts when the surrounding sandflats are underwater.

The project is supported by Eurobodalla Shire Council, the NSW Marine Estate Management Strategy (MEMS); and TNC and the Australian Government through the Reef Builder initiative.

Beyond large-scale projects, grassroots initiatives are also driving change. A fisher-focused not-for-profit and other community groups are leading a shellfish restoration movement using citizen science and local stewardship.

As part of its mission to protect and restore waterways, OzFish Unlimited (ozfish.org.au) has a number of projects to rebuild oyster and mussel reefs.

In Perth’s Swan River, a citizen science initiative is engaging local fishers to monitor and report on the condition of mussel reefs. The lack of hard structure in the river has reduced the opportunities for mussels to settle and grow. With support from the TNC Reef Builder project, four limestone Blue Mussel (Mytilus galloprovincialis/plantulatus) reefs were constructed in the lower Swan-Canning Estuary between 2019 and 2023.

Recreational fishers are using remote underwater video units to monitor the fish communities on the newly established reefs to help gauge the effectiveness of Blue Mussel reefs to provide productive fish habitat.

Building on earlier restoration efforts, new projects are enhancing existing reef structures to improve habitat connectivity and climate resilience in urban estuaries.

From 2009 to 2012, the Victorian Fisheries Authority installed concrete reef balls across six locations in Port Phillip Bay to recreate lost structure. Using recycled shell from OzFish’s Shellsavers Project, and The Nature Conservancy’s Shuck Don’t Chuck program, volunteers will infill reefs and start creating ecosystems by dropping bagged shell from boats over the concrete reef balls. The two-year project, which began in late 2024, includes monitoring of fish species using baited remote underwater video systems.

As well as increasing overall habitat for fish and other species, the project could help the bay become more resilient to impending climate change impacts by buffering erosion through shoreline protection, sequestering carbon, and through the filtering and uptake of excess nutrients.

This case study was prepared by NCCARF.

Please cite as: NCCARF, 2024: Rebuilding Australia’s oyster reefs. Case study for CoastAdapt, National Climate Change Adaptation Research Facility, Griffith University, Gold Coast.