A multinational research team has traced the decade-long epidemic known as sea star wasting disease to a strain of the bacterium Vibrio pectenicida, a relative of the cholera pathogen. The findings, published 4 August in the journal Nature Ecology & Evolution, are the result of a four-year investigation led by scientists from the University of British Columbia, the Hakai Institute and the University of Washington. Since 2013 the disease has ravaged more than 20 sea-star species along the Pacific coast of North America, from Alaska to Mexico, causing lesions, arm loss and rapid disintegration. Researchers estimate the outbreak has killed roughly six billion individuals and wiped out about 90 per cent of the global population of the sunflower sea star (Pycnopodia helianthoides), now listed as critically endangered. Laboratory challenge tests showed that healthy sea stars exposed to cultures or fluids containing the FHCF-3 strain of V. pectenicida developed wasting symptoms and died within days, confirming the bacterium as a primary causative agent. The work replaces earlier, inconclusive virus theories and offers a clear target for future mitigation, including the development of diagnostic kits, selective breeding for resistance and potential antibiotic treatments. Scientists say rising ocean temperatures may enable Vibrio species to thrive, suggesting climate change could intensify future outbreaks. Understanding the pathogen is also critical for restoring kelp-forest ecosystems that have suffered as unchecked sea urchin populations expanded in the wake of the die-off.