Windara Reef - Lessons learnt from the first large scale oyster reef restoration in Australia

Shellfish reefs are a key component of the marine environment, cleaning coastal waters, supporting marine biodiversity, and reducing coastal erosion. A dramatic decline in the extent and condition of Australia's two most common shellfish ecosystems, developed by the Sydney Rock Oyster (Saccostrea glomerate) and the Australian Flat Oyster (Ostrea angasi), occurred during the mid-1800s to early 1900s due to extensive harvesting for food and lime production. Recent research has shown that oyster populations are at less than 1% of their pre-colonial extent in Australia, with only one known healthy Australian Flat Oyster reef remaining. During 2016 to 2019 an ambitious project was initiated to undertake the first large scale shellfish reef restoration in Australia. The Windara Reef was constructed across 20-hectares in the Gulf St Vincent, seeking to establish a healthy and sustainable reef system and provide a test-case for the future development and rehabilitation of Australian Flat Oyster communities in South Australia. The design of the reef sought to balance several conflicting priorities. These included stability, settlement, constructability, cost and most importantly the suitability for oyster colonisation. The design used a coupled wave and hydrodynamic model to inform the decision-making process. The selected design concept included the deployment of a wide graded limestone substrate that has been seeded with oyster spat grown on recycled oyster shell. The project received a merit award in the 2018 Environmental Business Journal Awards recognising the Environmental Restoration impacts of the project. This paper will provide a context for the need and benefits of the reef restoration works, detail the challenges that faced the design of the reefs and how the engineering design sought to balance the conflicting priorities. Using the understanding developed through this project the paper will conclude with recommendations to support future development and restoration works.