The largest man-made oyster reef system in the Southern Hemisphere is completed this week as seven million native oysters are released in South Australia.
The wild release of the hatchery-raised Australian Flat Oysters marks the final stage of three years of work to reconstruct natural shellfish reefs in Gulf St Vincent, South Australia.
The Windara Reef system is under 10 metres of water about a kilometre off the coast near the Yorke Peninsula town of Ardrossan.
The 20ha system was constructed from limestone boulders and concrete ‘reef balls’ in two stages in 2017 and 2018. About 80,000 hatchery-reared Australian Flat Oysters have already been released onto the reefs.
The project is a collaboration between The Nature Conservancy (TNC), the Government of South Australia, the Australian Government through the National Stronger Regions Fund, Yorke Peninsula Council and the University of Adelaide.
‘Getting the oysters out on the reef is a huge milestone for the project and marks the completion of the construction of Windara Reef,’ said TNC marine restoration co-ordinator Anita Nedosyko.
‘We’re already seeing millions of native oysters being naturally recruited onto the reef. The addition of seven million more from the hatchery will really give the reefs a tremendous boost.’
TNC has announced another native oyster reef system would be built in Gulf St Vincent off the coast of the state’s capital city Adelaide.
The new 2-ha reef is expected to be completed by the end of 2020 and is being partially funded with a $1.2 million investment from the South Australian Government.
‘Rebuilding these locally extinct reefs will bring back so many benefits to the Gulf and its local communities, including greater marine biodiversity, boosting fish productivity and improving water quality in the region,’ said South Australian Environment and Water Minister David Speirs.
Adult broodstock for the Windara Reef was collected from the wild by the South Australian Research and Development Institute and allowed to spawn naturally at its hatchery, with larvae collected daily.
The larvae then settled naturally on recycled oyster shells in 2000-litre tanks.
Volunteers from the Friends of Windara Reef group and across Yorke Peninsula helped prepare 25 cubic metres of recycled shells from South Australian oyster farms for use in the project.
The larvae and spat received a clean bill of health before being transferred to Windara Reef by Gribbles Veterinary Pathology to ensure diseases were not transferred into the wild.
The juvenile oysters are likely to begin producing their own spat (offspring) when they reach three years old. It is expected take seven years to create a fully functioning, self-sustaining reef.
However, early testing just six months after the first 30,000 oysters were seeded last year found the oysters to be surviving and a number of wild oyster spat had also made their way to the reef, which was an unexpected bonus.
Oyster reefs are considered the temperate water equivalent to coral reefs in tropical waters.
Australia’s southern coastline was home to thousands of kilometres of oyster reefs before European settlement but dredging to remove substrate for lime production and the harvesting of oysters for food wiped out all the reefs except for one off the coast of Tasmania.
Adult native oysters can filter more than 100 litres of water a day and excrete a mucus-like substance that is rich in nutrients and provides food for small shellfish that in turn provide food for larger fish.
The Nature Conservancy’s National Reef Building Project aims to rebuild 60 reefs in six years across Australia. If achieved, it will make Australia the world’s first nation to recover a critically endangered marine ecosystem. Projects in Melbourne’s Port Phillip Bay are also in advanced stages of reconstruction with others getting underway in Western Australia and Queensland.