Bacteria Identified as Cause of Sea Star Mass Die-Off

• Scientists trace decade-long sea star epidemic to Vibrio pectenicida, offering new hope for restoring marine ecosystems along the Pacific coast.

A Decade-Long Marine Mystery Resolved

Researchers have identified the bacterium responsible for a devastating epidemic that has killed over five billion sea stars along the Pacific coast of North America. The outbreak, which began in 2013, affected more than 20 species and led to a dramatic decline in populations from Mexico to Alaska. Most severely impacted was the sunflower sea star, which lost approximately 90% of its population within the first five years. The disease, known as sea star wasting syndrome, causes lesions, tissue decay, and ultimately disintegration of the animals’ bodies.

Initial investigations pointed to a virus, but further analysis revealed that the suspected densovirus was common in healthy sea stars and not linked to the disease. Researchers struggled for years to pinpoint the cause, often relying on tissue samples from dead specimens that lacked key biological fluids. The breakthrough came when scientists examined coelomic fluid—the internal liquid surrounding sea star organs—and detected the presence of Vibrio pectenicida. This bacterium, also known to infect shellfish, was confirmed as the primary agent behind the wasting disease.

Scientific Approach and Ecological Implications

The discovery was published in Nature Ecology and Evolution and marks a significant step in understanding marine epidemics. Marine disease ecologist Alyssa Gehman described the symptoms as “gruesome,” noting that infected sea stars lose their arms and collapse within days. The research team, led by the Hakai Institute and University of British Columbia, conducted controlled experiments to confirm the bacterium’s role. Their work has been praised by independent experts for its methodological rigor and ecological importance.

With the pathogen identified, scientists can now explore strategies to protect remaining sea star populations. Potential interventions include testing for natural immunity, relocating healthy individuals, and breeding sea stars in captivity for reintroduction. These efforts are critical not only for the species itself but for broader ecosystem stability. Sea stars play a key role in controlling sea urchin populations, which, when unchecked, can decimate kelp forests.

Restoring Balance to Coastal Ecosystems

The decline of sunflower sea stars has triggered a cascade of ecological consequences. In their absence, sea urchins have proliferated, consuming up to 95% of kelp forests in Northern California over the past decade. These underwater forests serve as vital habitats for fish, sea otters, and seals, and their loss threatens biodiversity and coastal resilience. Marine biologist Rebecca Vega Thurber likens kelp forests to “rainforests of the ocean,” emphasizing their importance to both wildlife and human communities.

Recovery efforts are now underway, with researchers considering probiotic treatments and selective breeding to enhance disease resistance. Conservation groups and aquariums have begun raising juvenile sea stars in controlled environments, aiming to reintroduce them into affected regions. The identification of Vibrio pectenicida opens the door to targeted monitoring and early detection of future outbreaks. Long-term success will depend on continued research and collaboration across scientific, governmental, and community sectors.