Aboriginal communities used Australia’s oyster reefs for thousands of years before European colonisation. More than just an abundant source of highly nutritious food, oysters provided an important trading resource for coastal communities, and their shells were used to fashion fishhooks and cutting tools.
Enormous shell middens containing billions of shells attest to their cultural significant, with unearthed shell deposits up to 400 meters long and 4 metres high. Carbon-dating has detected oyster remains up to 9,000 years old in Australia’s east coast middens, however middens any older were likely destroyed by rising sea levels. Some Aboriginal communities likely returned oyster shell to the water at their favourite harvesting spots to increase the settlement of baby oysters.
Therefore, Aboriginal oyster farming is likely the oldest form of aquaculture practiced in Australia, pre-dating European aquaculture by thousands of years.
In 1770 Captain Cook remarked on the great extent of oyster reefs in Sydney’s harbours, including the largest oysters he had ever seen. Eighteen years later the First Fleet had to navigate a patchwork of oyster reefs when they sailed into Sydney’s shallow bays, with individual reef patches covering up to 10 hectares. As the early colony struggled to grow their European crops, the low-hanging fruit of intertidal oyster reefs provided an essential food source for the colonists, without which they may have starved. The settlers soon started using oysters as a building resource, burning the shell to produce lime with which cement was manufactured.
The early foundations of colonial Australia were literally built on oysters.
Wherever new colonies were settled around Australia a thriving, unmoderated industry of harvesting oyster reefs quickly followed. Intertidal reefs were easily exploited with hand tools during the low tide, with oystermen able to work the same reef patch for weeks at a time before moving to the next. Advancing dredging techniques soon saw the indiscriminate harvesting of subtidal reefs.
Even the underlying bed of dead shells that provide essential substrate for the settlement of baby oysters was harvested for lime burning. Limekilns were built wherever the harvest was good, and even live oysters were burnt for lime until it was prohibited by the 1868 Oyster-beds Act. As oyster reefs disappeared around the major colonial settlements, the exploitation spread out across the coast, with the search for new oyster reefs fuelling the coastal spread of European settlements. By the 1860’s most of the oyster reefs were gone in NSW, with similar declines within half a century of settlement of other major colonies.
While records of the historic extent of these reefs are limited, in South Australia alone over 1,500 km were lost in the decades following settlement, hence the national loss would likely rival the extent of the Great Barrier Reef.
Today less than 1% of our historic reefs remain.
With the complete collapse of most wild oyster fisheries by the end of the 19th century oyster production transitioned to aquaculture using techniques similar to those used today. Despite the end of wild harvesting, oyster reefs have never recovered from the earlier exploitation. The loss of the enormous breeding populations and shell substrate for young to settle on, combine with the dramatic changes to the coastal landscape, changing the nutrient and sediment loads entering our coastal waters, and the introduction of oyster pests (i.e. mud worm) have all contributed to the lack of recovery.
The 20 hectare oyster restoration at Ardrossan demonstrates Australia’s determination to turn the tide on this historic loss. So much has changed in the short time since our oyster reefs were lost, so there are many questions to be answered on how oysters will response to contemporary environmental challengers.
The University of Adelaide will be tackling many of the big questions with generous support from South Australia’s Department of Environment, Water and Natural Resources, the Ian Potter Foundation, and the Environment Institute.
Stay tuned for more pearls of wisdom from this ambitious oyster reef project.
Dominic Mcafee completed his PhD in how oyster reefs build ecological resilience at Macquire University in Sydney. He is currently a Postdoctoral Researcher in Sean Connell’s lab and is heading the Oyster Reef Restoration Project in the Gulf St Vincent.