at Cabbage Tree Bay Acquatic Reserve, Manly, NSW
Snorkeller at Cabbage Tree Bay Acquatic Reserve, Manly, NSW © Peter McGree / TNC photo contest

Restoring shellfish reefs

Restoring Adelaide's lost shellfish reefs

Returning Australia’s endangered marine habitat to Adelaide’s shores

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Restore Australia's critically endangered shellfish reefs.

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Adelaide is a city of approximately 1.2 million people that lies on the eastern coast of the Gulf St Vincent or Wongga Yerlo in Kaurna language.

A healthy coast is a big part of Adelaide's current and past culture. It's enjoyed by swimmers, beach-walkers, surfers, divers, foragers and fishers—so we all want to protect it for future generations.

Across more than a third of the South Australian coastline, healthy shellfish reefs teeming with oysters, mussels, crabs, cuttlefish, prawns and fish once existed. 

Today, these ecosystems are among the most endangered marine habitats on Earth—with 85% loss worldwide.

Glenelg reef restoration

In November 2020, we built the first shellfish reef off the Adelaide coast near Glenelg. The reef spans over two hectares. It was made from 1,400 tonnes of limestone and seeded with around 1 million juvenile Australian Flat Oysters.

In 2021, we will be expanding the reef across an area of over five hectares. The expansion will further enhance the important ecosystem services this reef provides such as purifying water and helping fish populations by providing vital shelter for fish nurseries.

To ensure the reef is surviving well, we will be tracking its recovery over the next few years. Early signs are showing high density of oysters. Some of them the size of an adult's hand. We’re also seeing a variety of marine life visiting the reef including squid, whiting and blue swimmer crabs.

We’re also planning to build two more reefs in South Australia. Off the shores of Onkaparinga and Kangaroo Island. Not only will the restored reefs improve the health of the Gulf through more fish, cleaner water and increased biodiversity, they will also benefit the community and local economy through the creation of jobs during construction and increasing opportunities for recreation and tourism into the future.

Windara Reef, off the coast of Yorke Peninsula in Gulf St Vincent, was the first reef to be rebuilt in South Australia. To date, the 20 hectare reef is the largest restored shellfish reef in the Southern Hemisphere.

History of shellfish reefs

Historical fishing records show that shellfish reefs were once dominated by the Australian Flat Oyster. They were so prolific that they supported a significant oyster fishery in South Australia during the 1800s. In fact, in 1873 the very first legislation written in South Australia was a law to protect oyster beds from overfishing. This was even before the South Australian government was formed.

The discovery of ancient shell middens across the South Australian coastline also signifies the importance of oysters to Kaurna, Narungga, Nukunu, Ngarrindjeri, Banggarla and other Indigenous Australian diets.

It's estimated that shellfish reefs would have extended across more than 1,500km of South Australia's coastline from Eyre Peninsula to Adelaide.

Historical ecologist, University of Adelaide
A map showing a proposed area of oyster fishing closure (thick red outline) & an area to be opened to fishing (triangle). Aside photo of an oyster farmer
Gulf St Vincent 1889 A map showing a proposed area of oyster fishing closure (thick red outline) & an area to be opened to fishing (triangle). Aside photo of an oyster farmer © Randall 1911; Alleway and Connell 2015

With the exception of Windara Reef, we have no known native shellfish reefs left in South Australia today.

The disappearing shellfish reefs

When the first Europeans settled in Australia in the 1800s, large amounts of oysters were harvested for food to support the growing colonies. In the early 1900s the reefs, oysters which were rich in calcium carbonate, were dredged as a source of lime and construction materials to form the foundations of city infrastructure such as bricks and concrete.

Over time, nutrients and sediments within the fresh water running into Adelaide’s coastal waters reduced the ocean’s water quality and clarity. With extensive urban development, the Adelaide metropolitan coastline has experienced significant environmental degradation.

History of oyster management and reform in South Australia

The importance of shellfish reefs

Shellfish are ecosystem engineers. They provide habitat for around 100 species of fish and invertebrates (e.g. shrimps and crabs). They also filter water, stabilise sediment and transfer nutrients from the water column to the surrounding reef community.

By bringing back Australia’s most threatened marine ecosystem, these native shellfish reefs will return a wealth of benefits for people and nature including:

  • improved local fish populations as reefs act as fish nurseries
  • better water clarity due to the filtration power of oysters
  • increased shoreline protection
  • extra feeding habitat for threatened migratory shorebirds
  • an overall increase in biodiversity
  • increased opportunities for recreational fishing, economic development and tourism

 

David Speirs, Environment and Water Minister

"The new reef will be around the size of Adelaide Oval and is expected to be completed by late 2020. The Nature Conservancy is the world’s largest conservation organisation and has international and national expertise in reef restoration projects, including rebuilding over 60 reefs globally. I am looking forward to working with them to deliver a habitat that will boost fish productivity, create jobs and improve water quality in the region."

Shellfish reef restoration across Australia

This project is part of our bigger program to rebuild shellfish reefs across southern Australia. See our other shellfish reef restoration projects: