Rebuilding South Australia’s lost shellfish reefs
We’re restoring shellfish reefs that provide habitat, support marine life and contribute to healthier coastal environments.
What shellfish reefs are
Shellfish reefs are underwater habitats formed by native flat oysters and other shell‑forming species. Over time, shells accumulate and create low, complex structures that support marine life.
These reefs once occurred across South Australia’s gulfs and bays but were largely lost by the mid‑1900sthrough historical dredging and overharvest. South Australia is now bringing them back to rebuild habitat, support biodiversity, fish productivity, and contribute to coastal resilience.
Restored shellfish reefs are long-term habitat restoration projects. Ecological outcomes develop gradually over several years as shellfish settle and the reefs grow.
Fast facts
- Around 99% of South Australia’s historic shellfish reef ecosystems are functionally extinct.
- Shellfish reef structures create habitat used by fish, crabs and other marine life.
- Shellfish feed by filtering microscopic algae and particles from the water.
Why reefs matter for South Australia
- Biodiversity and habitat
Restored shellfish reefs provide structure, shelter, feeding areas and nursery habitat used by fish, crabs, invertebrates and other marine life. These habitats can support local fish abundance and productivity as reefs mature. - Ecosystem function
Shellfish act as ‘ecosystem engineers’. As they feed, they filter microscopic algae, cycle nutrients and produce waste that becomes fish food. These natural processes can help maintain local water clarity. - Stronger, more resilient coasts
Reef structures support local habitat condition and contribute to long-term coastal resilience. - Community and culture
Shellfish reef projects create opportunities for volunteering, education, shell recycling and community involvement. They support partnerships with Traditional Owners caring for Sea Country.
Timeline
- 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 with partners (Australian Government, The Nature Conservancy, and the University of Adelaide).
- 2023: Four restored reefs show strong early establishment (Windara, Glenelg, O’Sullivan Beach, Kangaroo Island).
- 2023: The University of Adelaide 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.
Our vision
A network of restored shellfish reefs in South Australia delivered through long-term investment and partnerships.
What we’re doing
The State and Commonwealth have invested in long-term coastal recovery. For shellfish reefs, this includes:
- $2.6 million for community reefs, shell recycling, and participation programs
- $10 million for large‑scale limestone reef construction
These investments build on the success and learnings of existing restoration sites and will scale restoration across the gulfs and Kangaroo Island.
Our reefs: results from a decade of restoration
Early monitoring across four restored reefs shows strong structure establishment and increasing biodiversity in the first years after construction.
Windara reef (near Ardrossan)
- Size: ~20 ha across 159 limestone reef bases
- Established: 2017
- Focus: Restore lost native oyster habitat and support local marine life
- Partners: Australian Government, The Nature Conservancy, University of Adelaide, Yorke Peninsula Council, RecFish SA.
Glenelg reef (Adelaide)
- Size: ~5 ha offshore from Glenelg
- Established: 2020
- Highlights: High native oyster densities and diverse fish observed
- Partners: Australian Government, The Nature Conservancy, University of Adelaide, City of Holdfast Bay.
O’Sullivan Beach reef (Onkaparinga)
- Size: ~5 ha about 500 m offshore
- Established: 2021
- Highlights: Designed for community access and monitoring
- Partners: Australian Government, The Nature Conservancy, City of Onkaparinga.
Nepean Bay reef (Kangaroo Island)
- Size: ~3 ha
- Established: 2022
- Focus: Support local biodiversity and local coastal economies
- 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.
Step 2: Prepare a stable base
Limestone or recycled shell in purpose-built bags is placed on the seabed to form reef patches.
Step 3: Seed with baby oysters
In spawning season (October to December) we deploy underwater speakers to play the sound of a healthy reef to attract baby oysters (‘spat’) – that naturally settle on the reef.
Step 4: Natural growth
Wild oysters continue to settle on the structure over time, growing the reef and attracting and supporting more marine life.
Results snapshot
- Area restored: 33+ hectares across SA
- Marine life: 100+ different marine species recorded across sites
- Community: 750+ volunteer hours contributed
- Ecosystem engineers: Shellfish act as ‘ecosystem engineers’. As they feed and grow, they help shape the habitat around them and support nutrient cycling and local food webs.
Frequently asked questions
Are these reefs aquaculture farms?
No. They are habitat restoration sites and not for harvest.
Can I fish near the reefs?
Yes. Normal rules apply unless signposted during construction where temporary closure protects the reef’s natural ecosystem while it is being established and allows marine life to settle. Please don’t anchor directly on reef modules.
Why can’t I take oysters from the reef?
Shellfish need to remain in place to grow the reef.
How were locations chosen?
Sites were selected for suitability, historic presence and community and industry considerations.
