Scientists have discovered the bacteria responsible for a ten-year epidemic that killed over 5 billion sea stars along the Pacific coast of North America. The outbreak, which began in 2013, stretched from Mexico to Alaska and harmed more than 20 species. The sunflower sea star suffered the most, losing about 90% of its population in the first five years. Sea star wasting disease causes open sores, loss of arms, and eventual death. Research published in Nature Ecology and Evolution identified the bacteria Vibrio pectenicida, which was also found in shellfish. This ends years of investigation, during which scientists mistakenly linked the cause to a virus.

The breakthrough came when researchers studied coelomic fluid, a liquid surrounding the organs of living sea stars, which revealed the bacterial source. Earlier studies only examined dead sea stars, which no longer contained this fluid. Experts say the next step is to check if some sea stars have natural immunity and if treatments such as probiotics can improve resistance. Plans may include moving healthy sea stars or breeding them in captivity for later release. Restoring sea star numbers is critical for Pacific ecosystems, as they control sea urchin populations. Without them, sea urchins have multiplied and destroyed about 95% of Northern California’s kelp forests, which are home to many marine animals.