Scientists Identify Karenia Cristata as Most Toxic Algae Behind South Australia Die-Off

Overview

• A peer‑reviewed study published this week in Nature Ecology & Evolution confirmed that Karenia cristata produced the brevetoxins linked to the South Australian harmful algal bloom and was identified through genetic mapping and toxin analysis.
• Laboratory bioassays and chemical tests showed K. cristata is about an order of magnitude more toxic than the next most toxic studied microalgae and caused strong effects at very low cell concentrations.
• The bloom began in March 2025, persisted for more than a year and drove widespread deaths of invertebrates, fish, mammals and birds while harming local fisheries and coastal communities.
• Karenia cristata had not been recorded in Australian waters before and was previously found off South Africa and near Newfoundland, which raises concern that similar cold‑water brevetoxin blooms could occur in other temperate coasts.
• Researchers are urging immediate expansion of targeted monitoring, routine brevetoxin testing for aquaculture and public‑health planning, and further ecological and genetic study to guide future mitigation.