Scientists have identified the cause of a marine die-off that has killed billions of sea stars since 2013, resolving a mystery that persisted for over a decade. Research published in Nature Ecology & Evolution points to a bacterium distantly related to cholera, specifically a Vibrio species, as the culprit behind sea star wasting disease. This disease has devastated populations of the sunflower sea star, which has suffered the most severe losses, and has contributed to widespread decline in kelp habitats. Experimental evidence includes injecting material from diseased sea stars into healthy ones, which has helped scientists understand the pathological process. The discovery sheds light on one of the largest marine die-offs ever recorded and may have broader implications for understanding bacterial impacts on marine ecosystems.