1.4 million juvenile oysters soon to call Kurnell shellfish reefs home

The Nature Conservancy (TNC) is excited to announce that approximately 1.4 million juvenile Australian Flat Oysters will be added to the newly restored shellfish reefs at Kurnell in Botany Bay, NSW, in early May.

This is the second round of 'seeding' juvenile oysters onto the reef bases, and importantly marks the first remote setting of Australian Flat Oysters for the Botany Bay shellfish reef restoration project.

Remotely setting young oysters, or spat, onto shells on the banks of the restoration site, as opposed to a hatchery located off-site, is a technique TNC has been developing in Australia and has now near perfected. This approach offers a higher survival rate of the young oysters due to reduced risks during transport and holding of oysters before deployment. It also offers a great way for local delivery partners and community to get involved in the restoration process.

In 2023, TNC, in collaboration with NSW Department of Primary Industries-Fisheries and Greater Sydney Local Land Services, restored 3.1 hectares of Australian Flat Oyster reefs in Kurnell, Botany Bay, as part of the Reef Builder Program, a national partnership between TNC and the Australian Government to restore lost shellfish reef ecosystems at 13 locations across southern Australia.

Kirk Dahle, South-East Coordinator for TNC’s Seascapes team, said that nine months after the rock reef bases went into the water, they have become naturally colonised with abundant marine life that are using the new structures as habitat.

“Recent observations from underwater cameras are showing very promising results, with native kelp and other colonising algae growing in multiple places on the reef, and more than 50 species of fish observed, including Snapper, Silver Trevally and multiple species of wrasse, compared to only one or two species of fish in the area before the restoration began,” he said.

The reef bases were first seeded with one million juvenile Australian Flat Oysters in June 2023, and are showing good survival rates. 

“To achieve that, we’re also taking the opportunity to use a new technique called remote setting right here in Botany Bay”.

Remote setting is an innovative way of growing juvenile oysters for shellfish reef restoration purposes. It was piloted for the first time in Australia by TNC at Kangaroo Island in 2022, and for the first time in New South Wales in Wagonga Inlet in 2023.

Typically, juvenile oysters (spat) are grown in a hatchery and settled on recycled shells (cultch). Once the oysters reach a certain size, the cultch is transported to the restoration site and scattered by hand onto the reef base, where over time they will attach and build complex structures.

With remote setting, however, the oysters at the free-swimming larval stage of their life cycle are settled onto recycled shell on the banks of the restoration site, and can be transported to the reefs soon after the oysters have settled.

Once collected from brood stock, the young Australian Flat Oyster larvae will be reared in a hatchery for approximately two weeks until they are ready to settle and “stick” to the recycled oyster shell. When they reach this stage TNC staff will transport them to Botany Bay and place them in tanks of seawater that contain the recycled oyster shell. The oyster spat will then settle onto the recycled shells in tanks at Robert Hill Endeavour Oysters in Woolooware Bay.

From here the recycled shell seeded with juvenile Australian Flat Oysters are manually spread onto the rock base at Kurnell, joining the oysters previously seeded. As soon as they are in the water, they will start filtering the water and provide habitat for fish and crustaceans.

“It is an exciting step in the life of this project. The reef is doing well. We are thrilled to see the variety of species around it and observe the oysters thriving in their new home,” Mr Dahle said. “This addition of more oysters to the reef will give it an extra helping hand and multiply its benefits to the local waterway and community.”