Kangaroo Island Oyster Reef Restoration Project

On this page:

• About the project
• The history of native flat oyster reef decline
• Why are oyster reefs so important?
• What are we doing to restore shellfish reefs?
• Collecting native oyster spat to seed these reefs
• Community input
• Where are these new reefs?
• Monitoring fish and shellfish life on the new reefs
• Thank you to our supporters

Image above from Stefan Andrews Ocean Imaging.

About the project

The Kangaroo Island Landscape Board has constructed 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 new reefs will provide habitat for premium recreational fishing species and contribute to a national initiative to restore shellfish reefs.

These low-profile artificial reefs have been constructed using limestone, recycled shell, terracotta tile and ceramic razorfish forms. The reefs will be seeded with local, native flat oyster spat that will be wild-caught from within the bay in autumn. 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 reef decline

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.

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.
  

What are we doing to restore shellfish reefs?

Construction of 20 small, low-profile reefs has been completed over the 2022-2023 summer in waters adjacent to Kingscote and American River. Each reef is approximately 100 m² in size and 3–4 m deep. The reefs have been placed in bare sand close to seagrass and rocky reefs to connect these productive coastal habitats for fish and invertebrates.

The reefs are made of limestone, oyster shells, terracotta tile modules and ceramic forms, providing a substrate for marine organisms to settle and grow on. These materials have been sourced locally, or are recycled, and include discarded oyster shells from The Oyster Farm Shop in American River.

We engaged the Goolwa Pipi Harvesting Company from the Fleurieu coast to deploy 200 tonnes of limestone to form the base for the reefs, with other materials placed amongst the rock piles. Ceramic and terracotta tile ‘razor forms’ have been recreated by ceramicist Jane Bamford and the Kingscote Men’s Shed respectively 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.

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 at the start of summer coinciding with the seasonal spawning of native flat oysters, to provide the young oysters with places to settle. Once the collected spat has grown for a few months and are big enough to resist predators, they 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 the project was first conceived. Community meetings, presentations and consultation with technical and scientific working groups and local industry were used to gather valuable knowledge of the historical and current state of native flat oysters around Kangaroo Island. This information helped select suitable reef locations and determine where to collect oyster spat. Local industry organisation KI Shellfish based in American River have been closely involved throughout the project, collecting spent oyster shell for the project, and deploying the terracotta tile modules to the reef.

Where are these new reefs?

The reefs have been built near the townships of Kingscote and American River. The sites were selected after consultation with the community, marine infrastructure agencies and local industry including 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.

The benefits of these reefs can be seen already, providing structure, which in turn attracts fish species targeted by recreational fishers. The encrusted surfaces will provide habitat for young fish and invertebrates. The flat oysters will take a few years to grow and produce their own larvae, and eventually become a restored reef reflective of those lost.

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. Now 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 over time and determine which materials and structures have provided the best habitat for our native flat oysters, and guide future oyster reef projects here on Kangaroo Island and across Australia.

Thank you to our supporters

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