Urgent action is needed to preserve the habitat of an Australian seafood staple, with new research finding that most of our local shellfish reefs have been destroyed or forgotten.
Flinders University marine biology experts warn that reef restoration has never been more important than it is now, with shellfish among the most affected species.
"As we approach the middle of the United Nation's Decade on Ecosystem Restoration, shellfish ecosystems have suffered enormous declines worldwide, including losses of up to 85 per cent of oyster reefs, and South Australia is no exception," Brad Martin, from the College of Science and Engineering, said in a new article in the journal Ocean and Coastal Management.
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The new research led by Martin, a PhD candidate, trawled through historical and archival records tracking centuries of South Australia's shellfish management, reviving new information on past reef ecosystems and management practices.
More than 140 shellfish reef locations were identified, which covered about 2630 square kilometres of the state's coastal waters – including about 887sq km of former native oyster reefs, and temperate coral oyster reefs.
Most of these shellfish reefs no longer exist today.
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Commercial wild oyster harvesting began in the 1840s, and more than 43 million oysters were consumed by the 1910s, based on historic shipping and landing records.
The high demand and potential declines motivated South Australia's earliest fisheries legislation (in 1853) and marine restoration efforts, including fishery closures (from 1875), shellfish translocation (from 1887), and marine reserves (from 1912).
"We found successful, large-scale oyster reef restoration historically occurred in Port Lincoln and Kangaroo Island in the 1910s, and community awareness of the impacts of shellfish reef loss to local fisheries and other marine life including snapper and whiting. These provide important case studies for future restoration efforts," Martin said.
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The records indicated that the reefs diminished in the past 200 years due to multiple factors, including destructive fishing, changes in resource management, and environmental contributors such as droughts and disease.
There are multiple projects in Australia, both governmental and citizen-led, now to restore and protect shellfish reefs, but Martin said further research was needed.
"Past records indicate that razor clams or 'razorfish' (Pinna bicolor) were foundational to establishing multi-species shellfish reefs in South Australia by providing natural settlement surfaces for oysters," he said.
"While razor clams and hammer oyster ecosystems can still be found today, the data demonstrates that these ecosystems are understudied and diminished. Future studies may unlock additional restoration opportunities to revive South Australia's native shellfish."
A senior author on the paper, marine biologist Dr Ryan Baring, said the lack of commercial appeal held by razor clams meant they had been less intensely studied.
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