Scientists have identified the bacteria responsible for a decade-long epidemic that killed more than 5 billion sea stars along the Pacific coast of North America. The outbreak, which began in 2013, extended from Mexico to Alaska and affected over 20 species, with the sunflower sea star losing about 90% of its population in the first five years. The condition, known as sea star wasting disease, causes lesions, loss of arms, and eventual death. The journal Nature Ecology and Evolution recently featured research revealing that the bacterium Vibrio pectenicida has been identified in shellfish as well. This discovery concludes years of investigative challenges, during which earlier research mistakenly attributed the cause to a virus. Researchers believe identifying the bacteria provides a foundation for conservation efforts to prevent further ecological deterioration.

The breakthrough came after scientists analyzed coelomic fluid—an internal fluid surrounding the organs of living sea stars—which revealed the bacterial culprit. Experts say this method was pivotal, as earlier studies examined only dead specimens lacking this fluid. Researchers now plan to explore whether some sea stars possess natural immunity and whether treatments like probiotics could enhance resistance. Recovery efforts may involve relocating healthy individuals or breeding them in captivity for later release. Restoring sea star populations is considered essential for the resilience of Pacific ecosystems, as these predators regulate sea urchin numbers. Without them, sea urchin populations have surged, destroying about 95% of Northern California’s kelp forests, vital habitats for diverse marine life. Researchers believe the discovery could aid in restoring sea star populations and in regenerating the essential underwater forests they help sustain.