The mystery of melting sea stars may finally be solved
A bacterium called Vibrio pectenicida is causing the mass marine die-offs
A sunflower sea star is reduced to goo near British Columbia’s Calvert Island in 2015. Sea star wasting disease has killed billions of animals. Identifying the culprit might help save this particular species.
Grant Callegari/Hakai Institute
A mysterious disease has been turning sea stars into goo since 2013. Now, there’s a leading suspect behind the killings — a bacterium called Vibrio pectenicida, researchers report August 4 in Nature Ecology & Evolution. Knowing the identity of the killer could help scientists protect both captive and wild populations of sea stars.
The disease, known as sea star wasting disease, is characterized by twisted arms, lesions and rapid death. One of the worst hit species is the sunflower sea star (Pycnopodia helianthoides), which lost almost 91 percent of its population — over a billion individuals — to repeated outbreaks in 2015, 2018 and 2023. This decline has consequences for ocean ecosystems, as sunflower sea stars are predators that keep sea urchin populations in check. In their absence, sea urchins have mowed down kelp forests, which absorb atmospheric carbon dioxide and support fish, otters, sea lions and other animals.
Identifying a pathogen responsible for wasting brings hope for P. helianthoides, says Ian Hewson, a marine ecologist at Cornell University. The study may be good news for rearing sunflower sea stars in captivity, “because you can treat them with antibiotics [that] would target that specific bacteria.”
In 2014, Hewson was part of a team that thought they had identified the pathogen responsible for deteriorating sea star populations. But the researchers couldn’t replicate their initial findings. Without knowing the identity of the sea star killer, protecting these creatures from the disease has been challenging, even in zoos and aquariums where sea stars are bred for potential restoration in the wild.
To identify the killer, marine disease ecologist Alyssa-Lois Gehman of the Hakai Institute in British Columbia and colleagues brought healthy-looking wild and captive-bred P. helianthoides to the U.S. Geological Survey Station in Marrowstone, Wash., where they quarantined the sea stars for two weeks to ensure they showed no signs of wasting.
Amy Chan, a marine microbiologist at the University of British Columbia, compares bacteria cultures from a sick versus a healthy sea star. The culture from the sick sea star (closest container) contains Vibrio pectenicida.
Then, the researchers dunked 50 sea stars in a tank where a wasting sea star had been, let them live with sick sea stars or injected them with diseased coelomic fluid, “essentially sea star blood,” Gehman says. All methods proved fatal: 92 percent of the once-healthy sea stars died within an average of about 12 days.
Next, the team looked for what spread the disease. Like humans, sea stars teem with bacteria, viruses and other microorganisms. The researchers analyzed the coelomic fluid of both healthy and sick sea stars for foreign genetic material.
At a team meeting in January 2024, Melanie Prentice, a marine ecologist at the Hakai Institute, presented genetic sequencing results that compared the microbial makeup of healthy and sick sea star coelomic fluid. Of the over 55,000 bacteria identified in sea star blood, one stood out — V. pectenicida. While some healthy sea stars also had V. pectenicida, it was in much smaller amounts.
To confirm the role of V. pectenicida, the researchers grew the bacteria in petri dishes and injected them into six healthy sea stars. Seven days later, all six were dead.
Hewson says that this was the strongest part of the study. But he is not convinced V. pectenicida is the smoking gun. In his previous attempts to look for a pathogen, V. pectenicida did not consistently turn up in wasting sea stars.
This discrepancy could be because previous studies looked for pathogens amid a hodgepodge of sea star tissues, Gehman says, while the current study focused on isolated coelomic fluid, where the contrast between healthy and sick sea stars is clearest.
Hewson disagrees. Sea stars can get sick for multiple reasons, but they “can only show us … in so many ways,” he says. “They lose their arms, sometimes they have lesions.” Disparate observations of wasting in different sea star species could have unrelated underlying causes. Still, this work could benefit sunflower sea stars.
Gehman is now working on rapid diagnostic kits — like the ones used for COVID-19 — so researchers can detect and treat V. pectenicida outbreaks in the field and act quickly.
