Rebuilding South Australia’s lost shellfish reefs
South Australia is rebuilding shellfish reef habitat that was lost over more than a century of dredging and overharvest to bring critical habitat, support marine life and contribute to marine ecosystem resilience over time.
What shellfish reefs are
Shellfish reefs are low, complex underwater structures built up from generations of native flat oysters and other shell-forming species settling on one another. They provide shelter, feeding areas and nursery habitat for fish, crabs and a wide range of marine life.
These reefs once occurred across South Australia’s gulfs and bays. They were largely lost by the mid‑1900s through historical dredging and overharvest and by the 1950s, flat oyster reefs were functionally extinct in South Australia.
Why they cannot recover on their own
Native oysters still spawn in South Australia's coastal waters every year. The problem is not a shortage of oyster larvae. It is a shortage of places for them to settle.
Oyster larvae need hard surfaces to attach to. They cannot survive on bare sandy seafloor. When dredging and overharvest removed South Australia's historic shellfish reefs, the hard substrate went with them. Without it, oyster larvae drift and die before they can establish. Shellfish reefs cannot naturally recover at scale on their own without restoring this lost hard substrate.
The program restores that missing substrate, placing recycled shell or limestone rock on the seafloor so native oyster larvae can settle, grow, and begin rebuilding lost reef structure and ecosystem function over time.
Why shellfish reefs matter
Shellfish are ecosystem engineers. They do not just inhabit their environment. They physically build and modify it, creating conditions that support a wide range of other species. The benefits of a restored reef extend well beyond the shellfish themselves.
- Habitat: Oysters and other shellfish grow together to form complex three-dimensional structures on the seafloor, providing shelter, feeding areas and nursery habitat for fish, crabs, invertebrates and other marine life. Fish abundance and diversity increase as reefs age and mature.
- Nutrient cycling and water clarity: As shellfish feed, they filter particles from the water, cycle nutrients and support local food webs. Filter-feeding oysters, mussels and clams can improve localised water clarity in suitable conditions.
- Ecological recovery and resilience: Restored reefs modify the physical structure of the seafloor, creating habitat that other species colonise over time. As reefs mature, they act as seed sources for surrounding habitat, rebuilding ecological foundations largely absent from South Australia's coastal waters for more than a century.
- Community and culture Reef projects create opportunities for volunteering, education, shell recycling and working with Traditional Owners caring for Sea Country.
What we are delivering
The Rebuilding South Australia's Lost Shellfish Reefs Program is delivering 26 community recycled shell reefs and 1 large-scale limestone reef.
26 community recycled shell reefs
26 community reefs are being built across Eyre Peninsula, Yorke Peninsula, Kangaroo Island and Largs Bay. 25 reefs are delivered by Adelaide University and 1 at Largs Bay by OzFish Unlimited. Each reef covers approximately 1 hectare of seafloor. Early consultation and reef building is underway. All 26 reefs are expected to be completed by 2028.
1 large-scale limestone reef
A large-scale limestone reef of approximately 16 hectares is planned in the Gulf of St Vincent off Yorke Peninsula, delivered by The Nature Conservancy. Limestone reefs are designed to restore reef substrate at a broader ecological scale. Construction is planned from late 2027, subject to approvals. Consultation with industry, communities and Traditional Owners is planned for the first half of 2026.
How locations are selected
Sites are selected based on historical reef distribution, feasibility and community and industry engagement. Potential sites are still being investigated and will be confirmed following consultation and regulatory approvals.
The program is led by the Department for Environment and Water and delivered in partnership with The Nature Conservancy, Adelaide University and OzFish Unlimited, with joint investment by the South Australian and Australian Governments.
South Australia's existing restored reefs
South Australia has been restoring shellfish reefs since 2017. Early monitoring across 4 restored reefs shows strong structure establishment and increasing biodiversity. Prior to the 2025 algal bloom, all reefs were showing encouraging signs against native oyster restoration benchmarks, with Glenelg stage 1 exceeding 50 adult oysters per square metre at 2.5 years post construction.
Windara Reef (near Ardrossan, Yorke Peninsula)
- Size: approximately 20 ha across 159 limestone reef bases
- Established: 2017
- Partners: South Australian Government, Australian Government, The Nature Conservancy, Adelaide University, Yorke Peninsula Council, RecFish SA
Glenelg Reef (Adelaide)
- Size: approximately 5 ha
- Established: 2020
- Partners: South Australian Government, Australian Government, The Nature Conservancy, Adelaide University, City of Holdfast Bay
O'Sullivan Beach Reef (Onkaparinga)
- Size: approximately 5 ha
- Established: 2021
- Partners: South Australian Government, Australian Government, The Nature Conservancy, City of Onkaparinga
Nepean Bay Reef (Kangaroo Island)
- Size: approximately 3 ha
- Established: 2022
- Partners: Australian Government, The Nature Conservancy, Kangaroo Island Council.
How reefs are built
Step 1: Choose suitable sites - Sites in historic reef areas with good water flow and appropriate depth are identified through science, monitoring data and community engagement.
Step 2: Prepare a stable base - Limestone or recycled shell in purpose-built bags is placed on the seafloor to form reef patches. This provides the hard substrate oyster larvae need to settle.
Step 3: Attract juvenile oysters - In spawning season native baby oysters (spat) naturally settle on new reef substrate. Research led by Adelaide University has shown that reef sounds attract baby oysters and other marine species to settle on new reef structures. We can use underwater speakers play sounds recorded at healthy reefs to increase settlement on new reefs.
Step 4: Nature takes over - Wild oysters settle and grow on the structure over time, growing the reef and attracting and supporting more marine life. As the reef matures, fish numbers and biodiversity increases.
Timeline of shellfish reef restoration in South Australia
- 1840s: Commercial oyster harvest begins in South Australia.
- 1950s: Historic flat-oyster reef systems become functionally extinct.
- 1996: Legislative protections for intertidal rocky reef ecosystems introduced.
- 2017: The South Australian Government begins restoring shellfish reefs in partnership with the Australian Government, The Nature Conservancy, and Adelaide University.
- 2023: Four restored reefs show strong early establishment (Windara, Glenelg, O’Sullivan Beach, Kangaroo Island).
- 2023: Adelaide University and Eyrelab begin the Reviving Coffin Bay's Lost Oyster Reefs project with community.
- 2023: OzFish deploys 70 ‘Robust Oyster Baskets’ with community volunteers in the Port River Estuary.
- 2025: The South Australian Government commits to rebuilding our lost shellfish reefs.
- 2026:The Rebuilding South Australia's Lost Shellfish Reefs Program begins delivery of 26 community recycled shell reefs across Eyre Peninsula, Yorke Peninsula, Kangaroo Island and Largs Bay, and commences consultation on a large-scale limestone reef of approximately 16 hectares off Yorke Peninsula
Frequently asked questions
Are these reefs aquaculture farms? No. Restored reefs are habitat restoration sites. Harvesting of oysters or other shellfish from restored reefs is not permitted at any stage. This is consistent with all previous shellfish reef restoration sites in South Australia.
Can I fish near the reefs? Normal rules apply unless signposted during construction, where a temporary closure protects the reef while it establishes and allows marine life to settle. Do not anchor directly on reefs.
How were locations chosen? Sites were selected for suitability, historic presence and community and industry considerations.
Can I volunteer to help build the reefs? Yes. Adelaide University and OzFish Unlimited work with local communities on shell recycling and reef building events.
