Toxic Algae in South Australia: A Potential Global Threat

A vast and lethal algal bloom has wreaked havoc in South Australia over the past eight months, impacting over 20,000 square kilometers of marine habitat. An estimated 1 million animals from more than 550 species have perished, significantly affecting human health as well.

Researchers have recently pinpointed the species responsible for this ecological calamity, cautioning that it represents a “new international threat with unpredictable outcomes.”

The alarming agent is a type of algae known as Karenia cristata. Previously, it was documented only in two locales near South Africa, where it resulted in fish die-offs in 1989 and the mid-1990s, as well as off the coast of Newfoundland, Canada.

The research team has also identified a novel toxin released by K. cristata, which belongs to a group of compounds called brevetoxins. These toxins can inflict neurological harm on marine creatures, damage fish gills, and lead to fatalities in various species, including sea dragons, great white sharks, and dolphins. Brevetoxins pose a risk to humans via inhalation or ingestion.

Team member Shona Murray, a professor at the University of Technology Sydney, expressed concern among international colleagues regarding the implications of a new toxin-producing species potentially appearing in their waters.

“We are aware that this algal bloom has the capacity to proliferate in other parts of the world,” she cautions. “Previously, we underestimated its ability to create extensive and destructive blooms that could persist for eight months.

“Now we have confirmation, and it’s evident that it’s already occurring in other global regions; thus, I consider it an international threat.”

Murray and her research team noted that nearly 850 instances of harmful marine algal blooms have been documented worldwide from 1985 to 2025, with the recent South Australian event considered “one of the most severe and widespread” ever recorded globally.

The researchers have yet to determine the reason for such a vast and lethal bloom. The rising frequency of harmful blooms globally has been linked to increasing ocean temperatures, and the outbreak coincided with a significant marine heatwave, where water temperatures soared up to 3 degrees Celsius above normal. Nevertheless, the unexpected expansion of the blooms occurred after May 2025 when ocean temperatures began to decline.

K. cristata researchers emphasize the urgent need to comprehend the triggers for the bloom, noting that, given the right circumstances, it could impact numerous countries.

Christopher Keneally from the University of Adelaide points out that the dominant Karenia species previously identified, Karenia mikimotoi, is not known for producing brevetoxins. “There are numerous uncertainties regarding how the specific toxins produced by this species influence humans,” he states.

He concurs that the discovery raises concerns about potential new threats arising beyond Australia. “Given this species’ wide global distribution, it’s likely already present in small quantities in various coastal areas worldwide,” he adds. “As nutrient levels rise in many urbanized coastal regions and sea surface temperatures escalate, we can rightly predict that a variety of bloom-forming organisms will become increasingly prevalent.”