Algae which caused brevetoxins in SA algal bloom most toxic of its kind studied

The algal bloom devastated South Australia's coastline, resulting in the deaths of significant numbers of marine life. (ABC News: Che Chorley)

A dominant species of algae in the bloom which devastated South Australia's coastline has been found to be the most toxic of its kind to be studied, according to an Australian-led research team.

Karenia cristata was identified by the research team as the algae causing brevetoxins in November 2025, with the new research finding the laboratory-grown strains of it were highly toxic, even in very low concentrations.

It was found there could potentially be a bloom anywhere with similar coastal water conditions.

The algae responsible for the brevetoxins in South Australia's devastating algal bloom is the most toxic species studied of its kind, according to newly published research.

The research has been undertaken by an Australian-led team, which last year identified Karenia cristata as a dominant algal species in the bloom that resulted in mass deaths of coastal wildlife and impacted SA's coast for over 12 months, since it was discovered in March 2025.

The research involved conducting experiments on laboratory-grown strains of Karenia cristata to assess its toxicology, as well as the toxicology of water samples from the bloom.

The algal bloom was first detected along Waitpinga Beach in South Australia's Fleurieu Peninsula in March 2025. (ABC News: Caroline Horn)

Adelaide University associate professor Craig Styan, who was one of the researchers, said the results showed that in the laboratory the algae species was highly toxic, even in very low cell concentrations.

"Just a few thousands of cells per litre can have a really quite large biological effect, which is a much stronger effect than we've seen in other harmful algae when they've been tested in similar ways overseas," he said.

Dr Styan said the testing helped them to understand why there were such significant effects from the bloom.

"We knew this bloom caused really big marine mortality events, and we knew there'd be brevetoxins, but we still didn't have a really good scientific explanation for why the impacts we were seeing was so extensive," he said.

"It shows Karenia cristata was exceptionally harmful to marine organisms when we tested it in some standardised laboratory tests.

Brevetoxins were detected in foam on metropolitan beaches in August 2025. (ABC News: Che Chorley)

Dr Styan said in his experimenting on microscopic zooplankton and brine shrimp, or sea-monkeys, it was surprising to see how sensitive the organisms were to the algae.

"It's re