Toxic algae blighting South Australia could pose a global threat

Over the past eight months, a large and deadly algal bloom in South Australia has ravaged more than 20,000 square kilometers of marine environment, killed around 1 million animals from more than 550 species and had far-reaching consequences for human health.

Now, researchers have finally identified the species causing this ecological disaster and warn that it represents an “emerging international threat with unknown consequences.”

The culprit is a species of algae called Karenia cristatawhich has previously only been reported from two locations near South Africa, where it caused fish kills in 1989 and again in the mid-1990s, and off the coast of Newfoundland, Canada.

The team also identified a new toxin produced by K. cristata which belongs to a class of compounds called brevetoxins. These can cause nerve damage to marine life and damage fish gills, killing animals ranging from sea dragons to great white sharks and dolphins. Brevetoxins are also harmful to humans when inhaled or ingested.

Team member Shauna Murray from the University of Technology Sydney, Australia, says the discovery has raised concerns among her overseas colleagues about what it could mean to have a new toxin-producing species “could appear in their waters.”

“We know that it can flourish in other countries around the world,” she explains. “What we didn’t know was that cristata produces brevetoxins and could cause these harmful algae outbreaks that are so huge and disruptive and last for eight months.

“Now we know it and, because we know it’s happening elsewhere in the world, yes, I think it’s an international threat.”

Of nearly 850 deadly marine algal blooms reported worldwide between 1985 and 2025, the current event in South Australia is “among the most destructive and widespread” ever reported worldwide, according to Murray and colleagues.

The team doesn’t know exactly what caused such a massive and deadly bloom. Around the world, an increased frequency of harmful blooms has been associated with higher seawater temperatures, and the start of the bloom coincided with a severe marine heatwave that resulted in water temperatures up to 3°C higher than normal. But the bloom expanded unexpectedly after May 2025, when the sea had started to cool.

K. cristata could potentially affect many countries with suitable conditions, so there is an urgent need to understand what could trigger a proliferation, researchers say.

Christopher Keneally of the University of Adelaide in Australia says that the dominant Karenie flowering species were previously thought to be Karenia Mikimotoiwhich is not known to produce brevetoxins. “Much is still unknown about how the specific toxins produced by this species affect humans. »

He agrees that the discovery raises the prospect of an emerging threat beyond Australia. “Given the wide global distribution of this species, it is likely that it already occurs in low abundance in many coastal areas of the world,” he says. “As we begin to see increased sea surface temperatures, as well as increased nutrients in most urbanized coastal areas, we can safely expect to see more bloom-forming organisms.”