Research has highlighted the importance of shellfish reef habitats to the quality of the marine environment, fish breeding, and water quality and to deliver recreational and economic opportunities. Native oyster reefs are now absent from South Australia’s waters, aside from the recently re-established Windara Reef off the coast of Ardrossan, on the Yorke Peninsula.
A second shellfish reef for South Australia is now planned for Adelaide’s metropolitan waters in the Gulf St Vincent. The South Australian Government has committed $1.2 million towards building South Australia’s metropolitan shellfish reef. The global conservation organisation, The Nature Conservancy, is leading the construction of the project in partnership with the South Australian Government. This project is expected to be completed by late 2020.
How many shellfish reefs are in South Australia?
Shellfish reefs, with mainly Australian flat oysters (Ostrea angasi), were common in South Australia’s gulfs and bays in the 1800s. Researchers estimate that they once spread across 1500 km of coastline.
Today, no native oyster reefs remain – mainly because of the impact of overfishing, dredging, water pollution and disease.
South Australia’s first re-established shellfish reef - 20-hectare Windara Reef off the coast of Ardrossan - was completed in November last year.
What are the location options?
Public feedback is now being sought on the location of the Adelaide Oval sized reef, which will be re-established in Adelaide metropolitan waters of the Gulf St Vincent.
Science and advice from experts have narrowed down the location options to three, they are:
- Glenelg, between Glenelg jetty and West Beach boat ramp.
- O’Sullivan Beach, between Christies Beach and O’Sullivan Beach boat ramp.
- Port Noarlunga, between Port Noarlunga jetty and Onkaparinga River mouth (within Encounter Marine Park Port Noarlunga Sanctuary Zone).
How were the location options selected?
A 70 km region of Adelaide’s metropolitan coastline was assessed from Port Adelaide to Sellicks Beach.
A spatial map of suitable areas was compiled, reviewed and refined by a team of restoration experts and marine scientists.
Three locations - Glenelg, O’ Sullivan Beach and Port Noarlunga - were selected based on accessibility, water depth, seabed composition, cultural sensitivity, historical locations of shellfish reefs and current environmental conditions, all to ensure that the restored shellfish reef can grow and thrive.
Why does South Australia need more shellfish reefs?
Research has highlighted the importance of shellfish reef habitats to the marine environment, fish breeding, and water quality and to deliver recreational and economic opportunities.
Shellfish reefs, just like coral reefs, provide homes for many marine species, while also helping to clean seawater through the natural process of filter feeding.
Also oysters are excellent water filterers, with each filtering up to 150 litres of water a day, which can help improve local water conditions and support the return of other ecosystems like seagrass.
What are the opportunities of the project?
The shellfish reef will provide:
- Tourism and coastal businesses opportunities. This project will provide a new nature-based tourism destination right off the Adelaide metropolitan coast for those interested in kayaking, diving and learning more about the marine environment.
- Community groups and individual opportunities. This project will provide citizen scientists and other volunteers another way to connect with South Australia’s marine environment.
- School and university educational opportunities. This project presents an exciting opportunity for students to learn first-hand about marine habitat restoration. Students can be involved in research, monitoring and other citizen science activities that will directly improve South Australia’s understanding of shellfish reef restoration.
- Recreational and commercial fishing opportunities. This project will build a habitat that supports fish breeding in South Australian waters.
How will South Australia’s metropolitan shellfish reef be built?
Following detailed design and engineering, the 2 hectares shellfish reef will be constructed using a limestone reef base, with hatchery raised Australian flat oysters.
Shellfish reef construction involves placing limestone rocks and recycled oyster shells onto the seafloor to provide elevation and hard calcareous surfaces for oysters to attach.
Once in place, the reef base will be seeded with millions of baby oysters, called oyster spat. The oyster spat are collected from local oysters spawned in a hatchery and set onto recycled shells. These shells are then deployed by divers onto the reef base.
The reef will be built in around 5 to 12 m depth of water, within 2 km of the shoreline. The exact reef design will depend on the final selected location.
What are the stages of shellfish reef development?
- In the first year, limestone substrate is laid on the seafloor and ‘seeded’ with juvenile native oysters (called spat) attached to recycled oyster shells.
- By the third year, spat grows and develops into larger oysters that spawn and increase the shellfish population on the reef.
- By the fifth year, the reef is attracting a range of marine species thanks to the food and shelter provided by the reef.
- By seven years and then beyond, the diversity and number of marine species increases as the reef acts as a nursery ground for fish, squid and crustaceans. The reef supports a diverse, productive and healthy marine habitat for the long-term.
- The reef is expected to be completed by late 2020.
- The reef will take time to grow and mature. After 10 years the reef will become a diverse and abundant natural ecosystem.
- Some fish species will be attracted to the reef in the short-term. Once mature, the reef will become an important fish nursey ground.
- Harvesting of oysters from the reef will not be permitted at any stage. This is to protect the oysters and allow the reef to thrive.