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Kangaroo Island Oyster Reef Restoration Project

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About the project

This project is constructing 20 small, native flat oyster shellfish reefs close to Kingscote and American River to restore the health and function of these important shellfish and fish habitats. The reefs will provide important habitat for premium recreational fishing species and contribute to a national initiative to restore shellfish reefs.

These low-profile artificial reefs will be constructed using limestone, recycled shell, timber modules, terracotta tile and ceramic razorfish forms. The artificial reefs will be seeded with local, native flat oyster spat that will be wild-caught from within the bay. Over time, the reefs are expected to grow and support the natural settlement of native flat oysters, and connect to form a continuous reef habitat.

This project is supported by the Kangaroo Island Landscape Board, through funding from the Australian Government’s National Landcare Program: Fisheries Habitat Restoration Program.

The history of native flat oyster reefs

Native flat oyster (Ostrea angasi) reefs were once widespread across southern Australia, including throughout Nepean Bay on Kangaroo Island, but were fished to near-extinction over a century ago. The remaining oyster shell was then dredged and used in construction, leaving no substrate on the seabed for new oyster larvae to settle and grow on. This project aims to restore this lost substrate so native oysters can settle and reinstate the lost benefits of this ecological community.

Kangaroo Island Oyster Reef Restoration Project

Oyster beds along the southern coast of Australia were dredged and used as construction materials in the 1800’s, leaving no substrate for baby oysters to settle and grow. (Image: Popular Science Monthly Volume 6)

Why are oyster reefs so important?

Native oyster reefs were once the keystone habitat of estuaries and coastal waters in southern Australia. The benefits of these reefs include:

  • providing crucial habitats for a broad range of temperate coastal marine species, such as King George whiting, southern calamari, seadragons and pipefish, and in doing so enhancing recreational and commercial fish and shellfish stocks
  • filtering water and improving water clarity and quality
  • stabilising sediment and protecting shorelines from storm surge wave-energy.
Kangaroo Island Oyster Reef Restoration Project

What are we doing to restore shellfish reefs?

Construction on the small, low-profile reefs will begin in early 2022 in waters adjacent to Kingscote and American River. Each reef will be 100 m² in size and will be 3–4 m deep. They will be placed in bare sand close to seagrass and rocky reefs to connect these productive coastal habitats for fish and invertebrates.

The reefs will be made of limestone, oyster shells, terracotta tiles, ceramic forms and timber, to provide a substrate for marine organisms to settle and grow on. These materials have been sourced locally, or are recycled, and they include oyster shells from The Oyster Farm Shop in American River.

The limestone rubble and oyster shells will be used as a base for the reef, with the other materials placed amongst them. Ceramic and terracotta tile ‘razor forms’ have been recreated to mimic the real razorfish that are found in Nepean Bay. Razorfish provide a natural surface for oyster larvae to settle on, including the native flat oyster found around Kangaroo Island. By placing these razorfish forms together in high densities and sheltering them between limestone patches, we aim to protect naturally settled baby oysters (spat) from predation while they are young. Similarly, modules have been made from timber stakes to create complex, protected structures with high surface areas, for the young oysters to settle on.

Kangaroo Island Oyster Reef Restoration Project

Diagram of the artificial reef.

Collecting native oyster spat to seed these reefs

There is a reliable source of native oyster spat in Western Cove, Nepean Bay but the substrate for it to attach to and grow on is missing. Spat collectors were placed in Nepean Bay in November 2021 to provide this young spat with places to settle. This coincided with the seasonal spawning of native flat oysters. Once the collected spat has grown for a few months and it is big enough to resist predators, it will be used to seed the new reefs.

Community input

The KI Landscape Board began consulting with the local community about these reefs in 2018, when the idea for project was first conceived. Community meetings, presentations and consultation with the technical and scientific working groups were undertaken. The local community provided valuable local knowledge and the local industry continues to give important insights and support, about the historical and current state of native flat oysters around Kangaroo Island. This information has helped select suitable reef locations and to determine where to collect oyster spat.

Where are these new reefs going to be?

The reefs will be built near boat ramps adjacent to Kingscote and American River. The sites were selected after consultation with the community, marine infrastructure agencies, industry, fishery and aquaculture stakeholders. A range of parameters were considered, including local marine biodiversity and habitats, depth, tide and wave conditions, proximity to boat launching facilities, focal species and the potential impact on other water users and vessel traffic. Both proposed sites near Kingscote and American River were ground-truthed using video tows to confirm that they were suitable for developing the reefs.

Kangaroo Island Oyster Reef Restoration Project

The proposed site for the artificial oyster reefs at Kingscote.

Kangaroo Island Oyster Reef Restoration Project

The proposed site for the artificial oyster reefs at American River.

Monitoring fish and shellfish life on the new reefs

Before the reefs were built each site was surveyed for fish species assemblages and abundance to create a baseline dataset. Once the reefs are built, the KI Landscape Board will closely monitor how well they are growing by surveying native flat oyster densities, growth and survival, and the abundance and diversity of fish, using Baited Remote Underwater Video Stations (BRUVs). This monitoring will be compared with the baseline surveys to detect any changes. This monitoring approach is consistent with other shellfish reef restoration projects established elsewhere in Australia.

Kangaroo Island Oyster Reef Restoration Project

A school of King George whiting travelling past a BRUVs bait station in Nepean Bay.

More information

Project Officer - Coasts

35 Dauncey Street Kingscote

08 8553 2476

ki.landscapeboard@sa.gov.au