The underside of an adult sunflower sea star at UW Friday Harbor Laboratories. Dennis Wise/University of Washington
Sunflower sea stars, the largest in the world with up to 24 arms, have faced a devastating epidemic since 2013. These majestic creatures, along with other sea star species along the west coast of North America, have been dying in alarming numbers. The symptoms are harrowing: contorted arms that eventually fall off. Over the past decade, sea star wasting disease has decimated billions of sea stars across up to 20 species by effectively “melting” their tissues.
The disease has eradicated more than 90% of the once-common sunflower sea stars, particularly in the continental U.S., leading to their inclusion on the International Union for Conservation of Nature’s Red List of critically endangered species. The disappearance of these stars, which are crucial for maintaining kelp forests by preying on kelp-eating sea urchins, has had far-reaching impacts on coastal ecosystems.
Unveiling the Culprit Behind the Epidemic
Until now, the cause of sea star wasting disease remained a mystery. However, on August 4, an international team of researchers, including scientists from the University of Washington, announced a breakthrough. They identified a strain of the bacterium Vibrio pectenicida as the culprit. Vibrio is a genus of bacteria notorious for its destructive impact on coral, shellfish, and even humans, with Vibrio cholerae being the pathogen responsible for cholera.
This groundbreaking discovery was published in Nature Ecology & Evolution. Drew Harvell, a co-author and UW affiliate professor in the School of Aquatic and Fishery Sciences, expressed his excitement:
“This is the discovery of the decade for me. We have studied both the cause and the impacts of this disease for the entire epidemic. What’s crazy is that the answer was just sitting right there in front of us. This Vibrio is a sneaky critter because it doesn’t show up on histology like other bacteria do.”
The Research Journey
The identification of the V. pectenicida strain FHCF-3 as the causative agent was the culmination of a four-year research process. Initially, scientists considered various pathogens, including viruses. The breakthrough came when researchers found high levels of V. pectenicida in the coelomic fluid, or “blood,” of sick sea stars.
Senior author Alyssa Gehman, a marine disease ecologist at the Hakai Institute and the University of British Columbia, described the moment of discovery:
“When we looked at the coelomic fluid between exposed and healthy sea stars, there was basically one thing different: Vibrio. We all had chills. We thought, ‘That’s it. We have it. That’s what causes wasting.’
Harvell credits the success to several factors:
- Access to the right facilities at the U.S. Geological Service with proper quarantine and high-quality water flow
- A talented research team with expertise in pathology, virology, and bacteriology
- Availability of test animals, including sunflower sea stars raised in captivity by co-author Jason Hodin, UW senior research scientist at Friday Harbor Laboratories
Confirming the Findings
To confirm V. pectenicida as the culprit, co-author Amy M. Chan, a research scientist at UBC, developed pure cultures of the bacterium from the coelomic fluid of sick sea stars. The team then injected the cultured pathogen into healthy sea stars, which subsequently developed symptoms of sea star wasting disease, providing the final proof.
Lead author Melanie Prentice, an evolutionary ecologist at the Hakai Institute and UBC, highlighted the broader ecological implications:
“When we lose billions of sea stars, that really shifts the ecological dynamics. In the absence of sunflower stars, sea urchin populations increase, which means the loss of kelp forests, and that has broad implications for all the other marine species and humans that rely on them. So losing a sea star goes far beyond the loss of that single species.”
Looking Ahead: Implications and Future Research
With the pathogen identified, scientists can now explore the drivers of the disease and potential resilience factors. Researchers are particularly interested in the connection between sea star wasting disease and rising ocean temperatures. Gehman noted that the disease’s effects seem more pronounced in warmer waters, and other Vibrio species are known to thrive in such conditions.
Researchers and project partners hope this discovery will guide management and recovery efforts for sea stars and the ecosystems affected by their decline. The team is now poised to investigate the environmental factors that exacerbate the disease and explore strategies for conservation and restoration.
