Scientists crack 12-year mystery behind sea star killing epidemic: Bacterium identified as marine mass killer

After more than a decade of devastation that has wiped out over 5 billion sea stars along the Pacific coast of North America, scientists have finally identified the cause of the catastrophic sea star wasting epidemic, marking a pivotal moment in marine science and ecological recovery efforts.

The crisis began in 2013, with sea stars from Mexico to Alaska rapidly succumbing to a mysterious wasting disease. Affected creatures exhibited gruesome symptoms: white lesions appeared on their bodies, their arms twisted and fell off, and ultimately, their bodies disintegrated into mush within days. The outbreak decimated at least 20 species, but none more so than the sunflower sea star (Pycnopodia helianthoides)—whose global population crashed by approximately 90–94% in just five years, with California suffering a staggering 99% loss.

Key discovery: The bacterial culprit
In a breakthrough study published Monday in the journal Nature Ecology and Evolution, an international research team pinpointed the bacterium Vibrio pectenicida as the epidemic’s cause. This bacterium, known to also infect shellfish, was found in high concentrations in the coelomic fluid (essentially sea star “blood”) of sick animals, and not in healthy ones—a crucial detail missed in countless earlier investigations that focused on dead tissue samples.


Dr. Alyssa Gehman, a marine disease ecologist at the Hakai Institute, described the impact: “It’s truly quite horrific... healthy sea stars display puffy arms extending outward, while the wasting disease leads to lesions, arm loss, and death.” Lead author Melanie Prentice also relayed the shock the research team felt when they finally isolated the bacterium.

Catastrophic ripple effects across Pacific ecosystems
The loss of sea stars—especially the sunflower sea star—triggered ecosystem upheaval: sea urchin populations, normally kept in check by sea stars, exploded. In turn, unchecked urchins destroyed vast kelp forests along the coast. Northern California alone saw up to 95% of kelp forests wiped out, erasing habitats and food sources for countless marine species and undercutting commercial fisheries.

“Almost everything that lives on the ground underwater runs away from them when they're coming,” said Dr. Gehman, emphasizing the sea stars’ role as a keystone predator. Their loss has been called one of the largest documented marine die-offs.

Recovery and resilience
Now that scientists have finally solved the mystery, attention turns to solutions. Identifying Vibrio pectenicida allows researchers to:

• Target remaining healthy sea star populations for conservation.
  
• Explore captive breeding and possible reintroduction programs.
  
• Investigate whether some sea stars harbor natural immunity, with the hope that probiotics or other treatments could help build disease resistance.
  

There is also interest in the role played by warmer ocean temperatures. Similar strains of Vibrio are known to amplify in warmer waters, suggesting climate change may exacerbate future outbreaks.