Algal Bloom

In reply to the Hon. C. BONAROS ().3 June 2025).

The Hon. C.M. SCRIVEN (Minister for Primary Industries and Regional Development, Minister for Forest Industries): I am advised:

Stansbury commercial shellfish harvest area was closed on 5 May 2025 due to the detection of Brevetoxins in oysters, a neurotoxic shellfish poison.

Brevetoxins are not produced by Karenia mikimotoi, the algae linked to fish deaths in waters around Fleurieu Peninsula, specifically near Waitpinga and Parsons Beach.

The presence of Karenia mikimotoi does not exclude the presence of brevetoxin-producing species of algae. More than one Karenia species can be present.

Brevetoxin is produced by specific microalgae species, such as Karenia brevisulcata, Karenia brevis and Karenia concordia.

Neurotoxin shellfish poison levels in shellfish above regulatory limits are harmful to humans if consumed.

Levels of brevetoxin initially detected in Stansbury were below regulatory limits. Following the initial detection, the South Australian Shellfish Quality Assurance Program (SASQAP) initiated weekly monitoring of oysters and has since detected levels above the regulatory limits.

This is expected as oysters are filter feeders and will accumulate the toxin while the algae remains in the water. It is expected there will be a delay between decreasing levels of algae in the water and the reduction of the toxin within the oysters.

Stansbury has remained closed since 5 May 2025.

Brevetoxins have also been detected in shellfish from harvesting areas of Coobowie, Port Vincent, American River and within the exclusion zone of the Coorong. These areas remain closed for commercial shellfish harvest and continue to be monitored weekly by SASQAP.

During the closure period, oysters remain viable with accredited oyster producers able to continue farming and grading oysters.

The reopening of any closed harvesting area will be in line with the South Australia Biotoxin Management Plan. This requires two consecutive weeks of shellfish samples showing a decline in brevetoxin levels that are below the regulatory limits. Water samples must also show a reduction in Karenia species.

Once the reopening process is complete, shellfish harvested from these areas will be available on the market as they will have met the food safety requirements and be safe to eat.

SASQAP has not received any reports of loss of oysters associated with the brevetoxin detections.