Toxin caused by algae forces quarantine of oysters on Yorke Peninsula

Australia Broadcast Center

07-05-2025

Health authorities have detected a waterborne toxin off Yorke Peninsula that has forced at least six oyster farms to temporarily shut and quarantine up to 10 million oysters.
Reports emerged overnight that the Department of Primary Industries and Regions South Australia (PIRSA) tested the waters at Oyster Bay in Stansbury last week and returned positive readings for brevetoxins which are produced by several species of karenia algae.
A PIRSA spokesperson said the department was still testing the samples and that "harvesting areas are often temporarily closed as a precautionary measure to ensure food safety standards are upheld."
A karenia algae bloom, believed to be caused by higher sea temperatures, has caused hundreds of dead marine life to wash up on SA shores over the past month.
Costly losses
Farmers using Oyster Bay have voluntarily cordoned off their sites, according to Pacific Estate Oysters owner Steve Bowley, who said he was awaiting further health advice from PIRSA.
The Pacific Estate oyster farm at Oyster Bay in Stansbury is under quarantine.
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Supplied: Steve Bowley
)
"We don't have any experience with this particular waterborne virus so we've temporarily closed the bay as a precautionary measure whilst we work out what's happening,"
Mr Bowley said.
"It means we can't sell any oysters out of the bay and if we wanted to transfer oysters to another bay … we need to get government permission to do that."
Mr Bowley said he was worried about losing "half a million dollars' worth of stock".
"We're not happy of course, but we would rather sell good oysters rather than them come back because people suddenly became sick," he said.
Climate change potential cause
Environment Minister Susan Close said rising temperatures caused by climate change likely played a role in the algae bloom that covered an area "not far off the size of Kangaroo Island".
Susan Close says a change in weather is needed to break up the bloom.
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ABC News: Che Chorley
)
"This is where nature is more powerful than we are, and the only thing that's going to break this algal bloom up is a change in the weather and strong westerly winds," Ms Close said.
"Normally we get that at the end of April and that hasn't happened yet. We need a big change in the weather to break this thing up."
Estuarine ecologist Faith Coleman said the toxins could have been caused by "six or seven" karenia variants.
"This one has developed into one of the more toxic species," Ms Coleman said.
"They develop toxins to protect themselves and to prevent other things from growing around them.
"We believe they do it to reduce grazing pressure on themselves."
It is unclear how long the affected oyster farms will be closed.