Bringing oyster reefs back from extinction

Oyster reefs carpeted thousands of kilometers of Australian coastline 200 years ago, but were dredged to near extinction within a century of colonial settlement. An ambitious nationwide restoration program now seeks to bring them back. In South Australia, the largest reef restoration in the Southern Hemisphere, Windara Reef, was constructed in 2017 to restore the ecosystem of the native mud oyster, Ostrea angasi, off the Yorke Peninsula.

Following construction of Windara Reef’s 149 individual reefs, a layer of fast-growing turf algae covered the new reef surfaces, forming a barrier to baby oysters trying to settle atop the reef. Such turf algae are a global phenomenon that is common on urbanised coasts where the algae opportunistically carpets hard surfaces.

To help restore South Australia’s lost oyster reefs, Prof Sean Connell and Dr Dominic McAfee of the Southern Seas Ecology Lab in the School of Biological Sciences and The Environment Institute developed a new multi-species approach to marine restoration.

This involved focusing not just on restoring oysters, but also on recovering other organisms that positively interact with the oysters to help them grow habitat. In this case, canopy-forming kelp, which form underwater forests that prevent turf algae from settling beneath their canopy, were transplanted atop Windara’s constructed reefs. Beneath the kelp canopies, the number of baby oysters that settled on the reef increased dramatically, accelerating the restoration process.

This multi-species approach to restoration will help create more resilient and stable ecosystems, and could reduce the cost of restoration by maximising natural recruitment processes, rather than needing to source expensive stock from hatcheries.

What’s next?

The success of the Windara Reef project has led the team to embark on a new multi-species restoration program in partnership with the South Australian Department for Environment and Water and aquaculture industries. This project is looking at the interaction between oysters, kelp, and abalone.