SYDNEY, July 10 (Xinhua) -- A rare microalgae species behind one of Australia's worst marine environmental disasters is among the most toxic to marine life ever recorded, according to a new Australian-led study.
Researchers identified the species, Karenia cristata, as the primary driver of a catastrophic algal bloom in the state of South Australia (SA) since early 2025, killing fish, seabirds, shellfish and marine mammals, and disrupting aquaculture and tourism, according to a statement released by Australia's University of Technology Sydney (UTS) on Thursday.
Local residents and tourists reported respiratory symptoms such as coughing and shortness of breath, as well as skin and eye irritation, the statement said.
Laboratory tests found the algae can kill zooplankton at concentrations as low as five cells per milliliter of seawater, making it more lethal than any comparable species studied using the same methods.
During peak periods in August and September 2025, concentrations routinely exceeded one million cells per liter of seawater off the coast of Adelaide, the SA state capital, according to researchers from the UTS and partner institutions.
Previously recorded only off South Africa and Canada, K. cristata was detected in 90 percent of samples collected during the SA harmful algal bloom, according to the study, published in Nature Ecology & Evolution.
Researchers said the findings suggest highly toxic algal blooms are not confined to warmer regions and warned that improved monitoring is needed to identify dangerous species to "protect our coastal ecosystems, industries and communities from another marine disaster." ■
