A massive and persistent algal bloom off the coast of South Australia has devastated the marine environment, killing an estimated one million animals and impacting human health. Researchers have now identified the culprit as the Karenia cristata species, raising concerns about a potentially widespread international threat due to a newly discovered toxin.
Understanding the Ecological Disaster
Over the past eight months, the bloom has impacted a staggering 20,000 square kilometers of marine habitat, resulting in the deaths of countless marine animals—an estimated million—belonging to over 550 different species. This ecological crisis also poses risks to human health, adding urgency to the need for further investigation.
Identifying the Culprit: Karenia cristata
While harmful algal blooms are not new, the specific algae responsible for this event is raising considerable alarm. Karenia cristata had only been previously documented in limited areas – near South Africa in the late 1980s and mid-1990s, and off the coast of Newfoundland, Canada—where it was linked to fish die-offs. This identification is a critical step in understanding and addressing the ongoing crisis.
A Novel Toxin: Brevetoxins and their Impact
Researchers have discovered that this particular strain of K. cristata produces a new type of toxin—brevetoxins. Belonging to a class of compounds known to cause nerve damage in marine life, these toxins can also severely damage the gills of fish and are harmful to humans if inhaled or ingested. This novel toxin production is a key factor in the bloom’s widespread impact.
“We know that it can bloom in other countries in the world,” explains Shauna Murray at the University of Technology Sydney. “Now we know that cristata produces brevetoxins and that it can cause these harmful algal outbreaks that are so huge and so disruptive and last for eight months. It is an international threat.”
Unprecedented Scale and Impact
The South Australian bloom stands out due to its duration and size, ranking among the most destructive and widespread algal blooms ever recorded globally since 1985. Researchers have documented nearly 850 deadly marine algal blooms worldwide during this period, but the current event’s scale is truly exceptional.
Potential Triggers and Global Concerns
While the precise cause of this massive bloom remains unclear, researchers suspect that warmer sea temperatures may have played a significant role. The bloom began during a severe marine heatwave—where water temperatures were 3°C higher than usual—and persisted even after water temperatures began to cool in May 2025. This unexpected longevity raises questions about the factors that allowed the bloom to continue.
Christopher Keneally at the University of Adelaide highlights a crucial point: “The dominant Karenia species in the bloom was previously thought to be Karenia mikimotoi, which isn’t known to produce brevetoxins. There is a great deal unknown about how the specific toxins produced by this species affect humans.”
Given the species’ potential to thrive in various coastal regions globally, researchers emphasize the urgent need to identify triggers that could initiate future blooms.
“Given the broad global distribution of this species, it is likely to already be present in low abundance in many coastal areas across the globe,” adds Keneally. “As we start to see sea surface temperatures increasing, along with high nutrients in most urbanised coastal areas, we can safely expect to see more of various bloom-forming organisms.”
The discovery of this toxin-producing Karenia cristata species highlights the potential for emerging threats to marine ecosystems and human health worldwide, emphasizing the importance of ongoing research and monitoring efforts.
