# Sea star wasting disease
Sea star wasting disease (SSWD) is a lethal disease of sea stars (starfish) that causes white lesions, loss of turgor, twisting and detachment of arms, and rapid tissue degradation that reduces the animal to a decayed mass, and which produced one of the largest marine epidemics ever recorded after emerging along the Pacific coast of North America in 2013[1](https://www.usgs.gov/centers/western-fisheries-research-center/news/solving-mystery-sea-star-wasting-disease-a). The outbreak spread from Mexico to Alaska, killed more than 5 billion sea stars, and devastated more than 20 species[2](https://apnews.com/article/f2ab802ae8787618a5905c566d38e0c5). In August 2025, researchers identified the cause as a strain of the bacterium *Vibrio pectenicida*, ending more than a decade of investigation[3](https://www.livescience.com/animals/mystery-of-why-sea-stars-keep-turning-into-goo-finally-solved-and-its-not-what-scientists-thought).
| Key fact | Detail |
|---|---|
| Onset | Mass die-offs began in 2013 along the Pacific coast, from Mexico to Alaska[2](https://apnews.com/article/f2ab802ae8787618a5905c566d38e0c5) |
| Scale | More than 5 billion sea stars killed; more than 20 species affected; the epidemic continues today[2](https://apnews.com/article/f2ab802ae8787618a5905c566d38e0c5) |
| Symptoms | White lesions, decaying tissue, twisted arms that break off, and "melting" of the body over a few days[1](https://www.usgs.gov/centers/western-fisheries-research-center/news/solving-mystery-sea-star-wasting-disease-a) |
| Cause | A strain of the bacterium *Vibrio pectenicida*, designated FHCF-3, identified in a study published August 4, 2025 in *Nature Ecology & Evolution*[3](https://www.livescience.com/animals/mystery-of-why-sea-stars-keep-turning-into-goo-finally-solved-and-its-not-what-scientists-thought) • [1](https://www.usgs.gov/centers/western-fisheries-research-center/news/solving-mystery-sea-star-wasting-disease-a) |
| Worst-hit species | The sunflower sea star (*Pycnopodia helianthoides*) lost about 90% of its population in the outbreak's first five years[2](https://apnews.com/article/f2ab802ae8787618a5905c566d38e0c5) |
| Environmental link | The disease surged during the intense 2013–2016 Pacific marine heatwave known as the Blob[4](https://www.noaa.gov/stories/new-edna-tool-to-help-track-recovery-of-sunflower-sea-star-pacific-coast-apex-predator) |
## Symptoms and course
The disease presents as a suite of non-specific signs: abnormal posture, epidermal ulceration, and limb autotomy, in which arms twist, develop lesions, and break off[1](https://www.usgs.gov/centers/western-fisheries-research-center/news/solving-mystery-sea-star-wasting-disease-a). A healthy sea star has puffy arms sticking straight out; affected animals develop lesions and then lose their arms, with tissue decaying over roughly two weeks until the body dissolves[2](https://apnews.com/article/f2ab802ae8787618a5905c566d38e0c5) • [3](https://www.livescience.com/animals/mystery-of-why-sea-stars-keep-turning-into-goo-finally-solved-and-its-not-what-scientists-thought). Similar outward signs can appear in sea stars suffering from other environmental stressors, which complicated diagnosis[3](https://www.livescience.com/animals/mystery-of-why-sea-stars-keep-turning-into-goo-finally-solved-and-its-not-what-scientists-thought).
## The search for the cause
**The densovirus hypothesis.** Within a year of the outbreak, investigators led by Ian Hewson of Cornell University proposed a densovirus as the causative agent, publishing "Densovirus Associated with Sea-Star Wasting Disease and Mass Mortality" in the *Proceedings of the National Academy of Sciences* in November 2014 with experimental evidence presented at the time as showing a pathogenic, transmissible disease[5](https://www.annualreviews.org/content/journals/10.1146/annurev-marine-040623-082617). Later investigation failed to support the initial results: subsequent studies found no consistent association between the virus and disease, and related densoviruses were shown to be persistent, phylogenetically widespread components of the normal sea star microbiome[6](https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2020.610009/full). A retrospective review concluded that critical reanalysis of the early experimental procedures disbanded any candidate agent[5](https://www.annualreviews.org/content/journals/10.1146/annurev-marine-040623-082617).
**The animal-water interface hypothesis.** A 2021 study proposed that microorganisms at the animal-water interface drive wasting: all aquatic surfaces are coated with a thin film of water, the diffusive boundary layer, which impedes gas exchange, and sufficiently high respiration can deplete oxygen at the animal's surface even when the water above is oxygen-saturated[6](https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2020.610009/full). Experiments amending seawater with organic matter substrates, including naturally collected particulate organic matter, caused faster wasting than controls[5](https://www.annualreviews.org/content/journals/10.1146/annurev-marine-040623-082617). Modeling studies also suggested that repeated sea surface temperature anomalies correlate with wasting[6](https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2020.610009/full).
**The Vibrio discovery.** The cause was finally pinpointed by a team led by the Hakai Institute and the [University of British Columbia](https://www.edgepedia.org/university-of-british-columbia), working with the USGS Western Fisheries Research Center's Marrowstone Marine Field Station in [Puget Sound](https://www.edgepedia.org/puget-sound), one of the few facilities where the study could be safely performed[1](https://www.usgs.gov/centers/western-fisheries-research-center/news/solving-mystery-sea-star-wasting-disease-a). Scientists sampled coelomic fluid, the fluid that surrounds sea star organs, from infected and healthy sunflower sea stars and used [DNA sequencing](https://www.edgepedia.org/dna-sequencing) to identify microbes present in infected but not healthy individuals, revealing *Vibrio pectenicida* strain FHCF-3 in a high proportion of infected animals[3](https://www.livescience.com/animals/mystery-of-why-sea-stars-keep-turning-into-goo-finally-solved-and-its-not-what-scientists-thought) • [1](https://www.usgs.gov/centers/western-fisheries-research-center/news/solving-mystery-sea-star-wasting-disease-a). Cultures of the bacterium given to healthy sea stars killed almost all of them, confirming the cause[3](https://www.livescience.com/animals/mystery-of-why-sea-stars-keep-turning-into-goo-finally-solved-and-its-not-what-scientists-thought). Earlier efforts had missed the pathogen partly because researchers studied dead sea stars whose coelomic fluid was no longer present[2](https://apnews.com/article/f2ab802ae8787618a5905c566d38e0c5). The genus *Vibrio* includes the agent of cholera and strains that have damaged coral and shellfish populations; other strains of *V. pectenicida* also disease cultivated scallops[3](https://www.livescience.com/animals/mystery-of-why-sea-stars-keep-turning-into-goo-finally-solved-and-its-not-what-scientists-thought) • [1](https://www.usgs.gov/centers/western-fisheries-research-center/news/solving-mystery-sea-star-wasting-disease-a).
## Ecological impacts
The sunflower sea star, an apex predator that feeds on kelp grazers such as sea urchins, was the worst-hit species[4](https://www.noaa.gov/stories/new-edna-tool-to-help-track-recovery-of-sunflower-sea-star-pacific-coast-apex-predator). Its loss contributed to the collapse of vast coastal kelp forests from the Aleutians to the Baja Peninsula: with predators removed, sea urchin populations surged and grazed kelp forests down to barren seafloor, and starving urchins continued grazing off new growth even after the marine heatwave receded[4](https://www.noaa.gov/stories/new-edna-tool-to-help-track-recovery-of-sunflower-sea-star-pacific-coast-apex-predator). In California, the sunflower sea star was nearly wiped out after the disease's onset in 2013[7](https://opc.ca.gov/wp-content/uploads/2025/11/Item-2-ED-Report-Dec-9-2025-508.pdf).
Recovery has differed sharply by species. In Oregon, more than 80% of ochre sea stars (*Pisaster ochraceus*) were killed in 2014, but researchers recorded an 8,000% increase in baby sea stars from pre-disease levels by 2015, and populations are now large enough that the species is resuming its role as a keystone predator of mussels[8](https://www.axios.com/local/portland/2025/11/04/ochre-sea-stars-rebound-oregon-coast). The sunflower sea star, by contrast, has not recovered: Canadian diving surveys suggest a loss of over 75% of that country's population with no evidence of recovery since 2015[9](https://www.canada.ca/en/environment-climate-change/services/species-risk-public-registry/cosewic-assessments-status-reports/sunflower-sea-star-2025.html), and its absence has fueled sea urchin booms and kelp forest declines[8](https://www.axios.com/local/portland/2025/11/04/ochre-sea-stars-rebound-oregon-coast).
## Conservation and monitoring
Disease is the primary threat to the sunflower sea star, and [NOAA Fisheries](https://www.edgepedia.org/noaa-fisheries) was petitioned in 2021 to list it as threatened or endangered under the Endangered Species Act; the species was proposed for listing in 2023[10](https://www.fisheries.noaa.gov/species/sunflower-sea-star/conservation-management) • [11](https://www.fisheries.noaa.gov/feature-story/dive-surveys-reveal-promising-signs-rockfish-and-sea-stars-washington-coast). In response to the outbreak, scientists brought surviving sunflower stars into captivity, an intervention that enabled successful captive spawning and supported the identification of *V. pectenicida* as the disease's primary driver[4](https://www.noaa.gov/stories/new-edna-tool-to-help-track-recovery-of-sunflower-sea-star-pacific-coast-apex-predator). A 2025 workshop convened by [The Nature Conservancy](https://www.edgepedia.org/the-nature-conservancy) brought together agencies, zoos and aquaria, tribes, and academic researchers to plan conservation breeding for the species[12](https://www.scienceforconservation.org/assets/downloads/Sunflower_Sea_Star_Conservation_Breeding_Workshop_Report.pdf).
Monitoring has expanded beyond diver surveys. NOAA's [Pacific Marine Environmental Laboratory](https://www.edgepedia.org/pacific-marine-environmental-laboratory) developed a rapid environmental DNA (eDNA) method that detects as few as a handful of copies of sunflower sea star DNA in a liter of seawater, returning results in one or two days; in 2026 it detected the species at six California sites, including the first detection south of San Francisco in a decade[4](https://www.noaa.gov/stories/new-edna-tool-to-help-track-recovery-of-sunflower-sea-star-pacific-coast-apex-predator). Wild sunflower sea stars were also verified by scientific divers in Mendocino and Sonoma counties in 2024 and 2025, and a refuge was found in Greater Farallones National Marine Sanctuary in August 2025[7](https://opc.ca.gov/wp-content/uploads/2025/11/Item-2-ED-Report-Dec-9-2025-508.pdf) • [4](https://www.noaa.gov/stories/new-edna-tool-to-help-track-recovery-of-sunflower-sea-star-pacific-coast-apex-predator). With the pathogen identified, researchers are now studying how sea stars respond to *V. pectenicida* under varying environmental conditions, since factors such as temperature and dissolved oxygen likely contributed to the pandemic and continue to interact with the disease to suppress recovery[1](https://www.usgs.gov/centers/western-fisheries-research-center/news/solving-mystery-sea-star-wasting-disease-a) • [13](https://repository.library.noaa.gov/view/noaa/72937/noaa_72937_DS1.pdf).
## References
1. [Solving the Mystery of Sea Star Wasting Disease: A Breakthrough Discovery, USGS Western Fisheries Research Center](https://www.usgs.gov/centers/western-fisheries-research-center/news/solving-mystery-sea-star-wasting-disease-a)
2. [Scientists say they have solved the mystery of what killed more than 5 billion sea stars, AP News](https://apnews.com/article/f2ab802ae8787618a5905c566d38e0c5)
3. [Mystery of why sea stars keep turning into goo finally solved, Live Science](https://www.livescience.com/animals/mystery-of-why-sea-stars-keep-turning-into-goo-finally-solved-and-its-not-what-scientists-thought)
4. [New eDNA tool to help track recovery of sunflower sea star, NOAA](https://www.noaa.gov/stories/new-edna-tool-to-help-track-recovery-of-sunflower-sea-star-pacific-coast-apex-predator)
5. [Lessons Learned from the Sea Star Wasting Disease Investigation, Annual Review of Marine Science](https://www.annualreviews.org/content/journals/10.1146/annurev-marine-040623-082617)
6. [Evidence That Microorganisms at the Animal-Water Interface Drive Sea Star Wasting Disease, Frontiers in Microbiology](https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2020.610009/full)
7. [OPC Executive Director Report, December 9, 2025](https://opc.ca.gov/wp-content/uploads/2025/11/Item-2-ED-Report-Dec-9-2025-508.pdf)
8. [Ochre sea stars make dramatic comeback in Oregon, Axios Portland](https://www.axios.com/local/portland/2025/11/04/ochre-sea-stars-rebound-oregon-coast)
9. [Sunflower Sea Star: COSEWIC assessment and status report 2025, Government of Canada](https://www.canada.ca/en/environment-climate-change/services/species-risk-public-registry/cosewic-assessments-status-reports/sunflower-sea-star-2025.html)
10. [Sunflower Sea Star: Conservation Management, NOAA Fisheries](https://www.fisheries.noaa.gov/species/sunflower-sea-star/conservation-management)
11. [Dive Surveys Reveal Promising Signs for Rockfish and Sea Stars off Washington Coast, NOAA Fisheries](https://www.fisheries.noaa.gov/feature-story/dive-surveys-reveal-promising-signs-rockfish-and-sea-stars-washington-coast)
12. [Sunflower Sea Star Conservation Breeding Workshop Report, The Nature Conservancy](https://www.scienceforconservation.org/assets/downloads/Sunflower_Sea_Star_Conservation_Breeding_Workshop_Report.pdf)
13. [NOAA West Coast Region environmental assessment document](https://repository.library.noaa.gov/view/noaa/72937/noaa_72937_DS1.pdf)
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*Topic: Encyclopedia › Life and health › Animals › Invertebrates › Other invertebrate lineages › Echinoderms and nonvertebrate chordates › Echinodermata (phylum and living classes) › Sea stars (Asteroidea) › Sea star health and disease*
*Initially written Sep 17, 2026 · Reviewed: Oct 21, 2026 · Edited: Oct 15, 2026; Oct 21, 2026 · Last review: Oct 21, 2026*
*Copyright 2026 EdgeChat AI, a subsidiary of Biostate AI.*
License: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license