Researchers have identified a bacterial species as the cause of sea star wasting disease, which has led to the death of billions of sea stars since 2013 and significant loss of kelp habitats. The bacterium, distantly related to cholera, was found to be particularly lethal to the sunflower sea star, the species most affected by the epidemic. This discovery resolves a 12-year mystery surrounding the widespread mortality of sea stars. The disease has had a profound ecological impact, with over 6 billion sea stars estimated to have died as a result.