Article by Mary Gordon
This is the story of how the ignorance and needs of mankind drove an essential ecosystem engineer of the Great Southern Reef to near extinction, and how generations of people forgot they even existed in the first place. How can this be? And what are we doing to fix it?
History of oysters on the Great Southern Reef
In the 1800s Australian flat oysters or Ostrea angasi (pictured above) were spread across 1500 kilometres of Australia’s southern coast and found commonly throughout South Australia’s gulf and bays. However, dredging, pollution and overfishing caused the species to become extinct.
The following timeline lays out the history of oyster fishing in South Australia and the loss of native oysters as a result of overfishing, water pollution and habitat loss.
A study by Alleway and Connell (2015) investigated historical police records to estimate the quantity of angasi oysters caught by commercial fishers from 1836 to 1944 finding a significantly reduced catch rate from 1886 until 1946 when they were mostly eradicated.
Interestingly, until recently there was no contemporary knowledge of their ecological importance and economic value. Alleway and Connell (2015) go on to discuss the concept of a shifted baseline.
Shifting baseline syndrome is where knowledge of the natural environment is lost over time because people do not perceive the changes taking place, and as the next generation is born, they will accept the state of the environment they are born into, resulting in an “intergenerational amnesia”. Alleway & Connell argue this phenomena “not only undermines progress towards their recovery, but also reduces our expectations of these coastal ecosystems.” This provides a challenge for restoration.
After this discovery people began to realise the potential benefits of native oyster reef reintroduction both to the environment and the economy.
The reintroduction of native oysters back to South Australia’s coast
In 2017 construction on Windara reef began as part of a $3.25 million project announced by the South Australian Government in order to boost the tourism economy, improve water quality, prevent coastal erosion and restore habitats crucial to supporting the fishing industry.
The project involved laying out 150 limestone blocks on the sandy seafloor.
Windara reef is located south of Ardrossan, on the Yorke Peninsula. Initially 4 hectares, it was expanded to 20 hectares in 2018, and in 2019, 50 000 Australian flat oysters were reintroduced to the restored reef. Now over seven million juvenile Australian Flat Oysters have been added to the reef.
Watch the video below to find out more.
Benefits of reintroduction
Firstly, Australian native oysters are an ecologically important species and it would therefore be beneficial for conservation efforts to prioritise the restoration of shellfish reefs.
Oysters have been identified as both a keystone species and an indicator species.
World Wildlife fund website describes a keystone species as “a species that plays an essential role in the structure, functioning or productivity of a habitat or ecosystem at a defined level… Disappearance of such species may lead to significant ecosystem change or dysfunction which may have knock on effects on a broader scale.”
The WWF definition of indicator species is “a species or group of species chosen as an indicator of, or proxy for, the state of an ecosystem or of a certain process within that ecosystem.”
Oysters are benthic filter feeders, meaning they get their food by feeding on suspended particles in the water. As a result of this, “Organisms living on sediments are able to bioaccumulate contaminants”
Bioaccumulation describes “the accumulation of contaminants in the tissues of organisms through any route”.
As a result, Native Oysters could be studied in order to detect and monitor the presence of contaminants in ocean sediments. Hence their reintroduction to South Australia’s coastline could inform responsible wastewater management.
Oysters are considered ecosystem engineers their shells provide the structural diversity in their environment and habitat for other species. The reefs they form act as a natural barrier against coastal erosion by reducing the erosivity of waves and stabilising sediments.
Furthermore, their role as filter feeders benefits other marine life as they are able to reduce turbidity and enrich sediments
Photograph (above) shows Australian flat oyster aquariums at the Marine Discovery Centre, Henley Beach. This display is used to demonstrate oysters’ ability to reduce turbidity.
McAfee, Larkin & Connel summarise that “the utility of bivalve–plant interactions in restoration research is predominantly positive across habitats and species “
Oyster reef reintroductions should be a high priority due to the environmental, social and economic benefits they provide. They have significant ecological value as keystone species, ecosystem engineers and indicator species which can serve the wider marine community and provide ecosystem services for people.
Ecosystem services provided by native oyster reefs include provisioning, regulating and cultural.
Native oysters support the fishing industry through serving marine habitats and enhancing fish recruitment. Through habitat provision, native oyster reefs promote the growth of sought-after species like Snapper and King George Whiting. This creates opportunities for both recreational and commercial fishers.
Furthermore, there is economic value in the farming of native oysters themselves. After the native oysters were fished to extinction, the market turned to the farming of pacific oysters. However, with the first recorded case of POMS (Pacific Oyster Mortality Syndrome) in Australia in 2018 the oyster industry took a hit and farmers have discussed the benefits of ‘diversifying’ by including angasi oysters into their farms.
This audio clip features an interview with Steve Leslie and Yvonne Young from the Oyster Province, an oyster farm that produces Australian flat oysters.
Through their ability to promote the health of marine ecosystems, oyster reef restoration also generates opportunities for nature-based activities for the locals and tourists to enjoy such as snorkelling, diving, fishing, dolphin/seal/ whale watching.
What can we do?
Would you like to try eating a native oyster one day? or continue to enjoy our states beautiful marine life on the Great Southern Reef? the best way you can help is by being educated. These crucial habitats were lost and forgotten in the past because the public were oblivious of their existence and importance. You can also help by getting involved with citizen science organisations such as the Estuary Care Foundation by offering your time as a volunteer (see photo below), or donating money through their website. Additionally, you can donate to the Nature Conservancy Australia’s shellfish reef restoration project
