AUGUST 4, 2025 - Today in Nature Ecology & Evolution, a group of researchers reveals the cause of sea star wasting disease (SSWD). This discovery comes more than a decade after the start of the marine epidemic that has killed billions of sea stars—representing over 20 different species from Alaska to Mexico. SSWD is considered the largest marine epidemic ever documented in the wild.
The challenging four-year investigation eventually pinpointed the microbial culprit behind SSWD: a strain of the bacterium Vibrio pectenicida.
Vibrio is a genus of bacteria that has devastated coral and shellfish as well as humans; Vibrio cholerae is the pathogen that causes cholera. A strain of V. pectenicida has previously been shown to wipe out the larvae of several species of scallops with a “swift and dramatic” course of infection.
In the case of sea stars, infection with the V. pectenicida strain FHCF-3 initiates a grim disease that begins with exterior lesions and ultimately kills sea stars by “melting” their tissues, a process that takes about two weeks after exposure. Afflicted individuals often become contorted and lose their arms.
The international research effort was led by scientists from the Hakai Institute, the University of British Columbia (UBC), and the University of Washington—and conducted in collaboration with The Nature Conservancy, the Tula Foundation, the U.S. Geological Survey’s Western Fisheries Research Center, and the Washington Department of Fish and Wildlife.
Over 90 percent of sunflower sea stars (Pycnopodia helianthoides)—which are capable of sprouting 24 arms and growing to the size of a bicycle tire—were wiped out by the disease in the past decade, landing them on the International Union for Conservation of Nature’s Red List of critically endangered species. The loss of sunflower sea stars, which support kelp forests by feeding on kelp-eating sea urchins, has had widespread and lasting effects on coastal ecosystems.
“When we lose billions of sea stars, that really shifts the ecological dynamics,” says Melanie Prentice, the first author on the study and an evolutionary ecologist at the Hakai Institute and UBC. “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.”
Kelp forests provide habitat for thousands of marine creatures and contribute millions of dollars to local economies through fisheries, recreation, and tourism. They’re also culturally important for coastal First Nations and tribal communities, they sequester and store planet-warming carbon dioxide, and they protect coastlines from storms.
“Understanding what led to the loss of the sunflower sea star is a key step in recovering this species and all the benefits that kelp forest ecosystems provide,” says Jono Wilson, the director of ocean science for The Nature Conservancy’s California chapter.
Identifying the disease in afflicted sea stars was impossible without a known pathogen, as sea stars can respond to other stressors and diseases with similar visual signals of contortion and loss of arms. The long-awaited result showing V. pectenicida as the causative agent comes after a four-year research process. The team of scientists explored many possible pathogens, including viruses, first looking in sea star tissues before homing in on the high levels of V. pectenicida in sea star “blood,” or coelomic fluid.
“When we looked at the coelomic fluid between exposed and healthy sea stars, there was basically one thing different: Vibrio,” says Alyssa Gehman, senior author of the study and a marine disease ecologist at the Hakai Institute and UBC. “We all had chills. We thought, That’s it. We have it. That’s what causes wasting.”
Amy M. Chan, a marine microbiologist in the Aquatic Virology and Microbiology Lab at UBC, then created pure cultures of V. pectenicida from the coelomic fluid of sick sea stars. Researchers then injected the cultured pathogen into healthy sea stars, and the ensuing rapid mortality was final proof that V. pectenicida strain FHCF-3 causes SSWD.
The research was supported by UBC, The Nature Conservancy, the Tula Foundation, and several other institutions, and conducted at the Aquatic Virology and Microbiology Lab at UBC, and at the Marrowstone Marine Field Station in Washington State, run by the U.S. Geological Survey’s Western Fisheries Research Center.
Now that scientists have identified the pathogen that causes SSWD, they can look into the drivers of disease and resilience. One avenue in particular is the link between SSWD and rising ocean temperatures, since the disease and other species of Vibrio are known to proliferate in warm water, Gehman says.
“Those patterns of Vibrio in general suggest that we really should look down that road to see how temperature dependence matters.”
Researchers and project partners hope the discovery will help guide management and recovery efforts for sea stars and the ecosystems affected by their decline.
“This finding opens up exciting avenues to pursue and expands the network of researchers able to develop solutions for recovery of the species,” says Wilson. “We are now actively pursuing studies looking at genetic associations with disease resistance, captive breeding of the animals, and experimental outplanting to understand the most effective strategies and locations to reintroduce sunflower sea stars into the wild.”
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Contact
Alyssa Gehman, senior author
Hakai Institute and University of British Columbia marine disease ecologist
(206) 251-9115
alyssa.gehman@hakai.org
Melanie Prentice, first author
Hakai Institute and University of British Columbia evolutionary ecologist
(236) 883-9988
melanie.prentice@hakai.org
Media Kit
Download the media kit that includes this press release, the newly published paper, videos, more information about the study, social media handles, and photos with captions.
About the Study
“The causative agent of sea star wasting disease” was published in Nature Ecology & Evolution in August 2025.
DOI: 10.1038/s41559-025-02797-2
https://www.nature.com/articles/s41559-025-02797-2
Learn more about the series of controlled experiments it took to isolate the microbial culprit behind sea star wasting disease.
Additional Facts
- Since 2013, sea star wasting disease (SSWD) has killed an estimated 5.75 billion sunflower sea stars (Pycnopodia helianthoides)—representing over 90 percent of their global population that extends from Alaska to Mexico.
- Worldwide, there are over 1,900 species of sea stars in 36 families. They can have five arms, like the ochre sea star (Pisaster ochraceus) found off North America’s west coast, or up to 50, like Labidiaster annulatus, a krill-eating sea star from Antarctic waters.
- Half of the world’s known sea star families are represented in the northeast Pacific Ocean where SSWD struck. Many species hit hardest by the disease, such as sunflower sea stars and ochre sea stars, are endemic to these waters, meaning they are found nowhere else on the planet.
- Both the SSWD causative agent and other Vibrio pathogens propagate in warm water, such as during marine heatwaves. According to recent evidence from a study led by Alyssa Gehman, ocean areas with consistently cold temperatures, such as the fjords of British Columbia’s Central Coast, could act as marine refuges for sunflower sea stars.
- Now that scientists know the cause of SSWD, they can shift their attention to recovery and treatment efforts. Potential interventions include testing individual sea stars and ecosystems for the pathogen prior to outplanting, and using probiotics, phage therapy, or other treatments to aid sea star health and recovery.
- The new study in Nature Ecology & Evolution was a major collaboration between researchers at the Hakai Institute, the University of British Columbia (UBC), the University of Washington, the U.S. Geological Survey’s Western Fisheries Research Center, and the Washington Department of Fish and Wildlife. It was funded by UBC, The Nature Conservancy, and the Tula Foundation, with research conducted at UBC’s Aquatic Virology and Microbiology Lab and at the Marrowstone Marine Field Station in Washington State, run by the US Geological Survey’s Western Fisheries Research Center.
Additional Quotations
Alyssa Gehman, marine disease ecologist at the Hakai Institute and the University of British Columbia’s Institute for the Oceans and Fisheries
“When we lost all of these sunflower stars, we ended up with huge populations of urchins. Those urchins then ate down the kelp forests. Until this event, we didn’t really grasp the importance of the link between sunflower sea stars and kelp. We knew sunflower sea stars ate urchins. We didn’t know how much they mattered until they all died.”
“Now that we found the causative agent of disease, it makes me more hopeful that we might actually be able to do something for sunflower sea stars,” Gehman says. “We can be really targeted in how we work with them, and I think that’s going to help us move a lot faster and to try to tackle sea star wasting disease.”
Melanie Prentice, evolutionary ecologist at the Hakai Institute and the University of British Columbia’s Department of Earth, Ocean, and Atmospheric Sciences
“It’s incredibly hard to work on solutions without knowing what the pathogen is. Getting this information makes management and recovery possible. Now all these doors are opened up to us, so we can start doing a lot more work to understand the drivers of disease and the roles played by different species.”
“I see a parallel with our human experience of going through the COVID-19 pandemic, and how much COVID tests really changed the way we interacted. Now that we know what causes sea star wasting disease, we can develop a test to screen samples, and that will tell us which animals we can move around and what areas are best for reintroduction.”
About the Partners
Hakai Institute
The Hakai Institute, part of the Tula Foundation, is a British Columbia–based scientific institution dedicated to advancing science on the coastal margin. Hakai pursues its mission from ice fields to oceans, leveraging its ecological observatories and other strategic locations on the province’s coast. The Hakai Institute partners with universities, NGOs, First Nations, government agencies, businesses, and local communities to move the needle on advancing long-term coastal research.
www.hakai.org
The University of British Columbia
The University of British Columbia is a global center for research and teaching, consistently ranked among the top public universities in the world. Since 1915, UBC’s entrepreneurial spirit has embraced innovation and challenged the status quo. UBC encourages its students, staff, and faculty to challenge convention, lead discovery, and explore new ways of learning. At UBC, bold thinking is given a place to develop into ideas that can change the world.
https://www.ubc.ca/
University of Washington College of the Environment
The University of Washington College of the Environment is one of the largest environmentally focused institutions in the United States, with leading-edge research from the depths of the oceans to the farthest reaches of the cosmos. Our faculty, researchers, and students drive solutions that safeguard our planet and improve our quality of life, building opportunities for a brighter, more sustainable future.
https://environment.uw.edu/
Tula Foundation
The Tula Foundation is a British Columbia–based organization that harnesses science and technology to tackle urgent global issues. Tula takes a comprehensive approach to these challenges, from coastal biodiversity and public health to data management and mobilization. Along with rural healthcare in Guatemala, Tula’s work drives pivotal action for coastal conservation and ocean research in British Columbia and beyond.
www.tula.org
The Nature Conservancy
The Nature Conservancy is a global conservation organization dedicated to conserving the lands and waters on which all life depends. Guided by science, we create innovative, on-the-ground solutions to our world’s toughest challenges so that nature and people can thrive together. In 81 countries and territories, we are tackling climate change; conserving lands, waters, and oceans at an unprecedented scale; providing food and water sustainably; and helping make cities more sustainable. To learn more, follow @nature_press on X or visit:
www.nature.org
U.S. Geological Survey Western Fisheries Research Center
The Western Fisheries Research Center (WFRC) is part of the U.S. Geological Survey (USGS), the nation’s primary agency dedicated to providing independent science for a changing world and in response to society’s continuously evolving needs. WFRC’s mission is to provide the science necessary to inform sustainable use and management of native fish species and aquatic ecosystems in the western United States. Through collaborative, multi-disciplinary science, WFRC helps resource managers from California to Alaska make informed, timely decisions on fish and aquatic species management. WFRC is internationally known for our expertise in studying complex food webs, addressing aquatic diseases, and providing decision support to improve water management for fish and people.
http://www.usgs.gov/centers/western-fisheries-research-center
Washington Department of Fish and Wildlife
The Washington Department of Fish and Wildlife works to preserve, protect, and perpetuate fish, wildlife, and ecosystems while providing sustainable fish and wildlife recreational and commercial opportunities.
https://wdfw.wa.gov/
Journal
Nature Ecology & Evolution
Method of Research
Experimental study
Subject of Research
Animals
Article Title
The causative agent of sea star wasting disease
Article Publication Date
4-Aug-2025
