Where to relay sea star data (of great value in understanding the survival, species impacted, range, and potentially, contributing factors of Sea Star Wasting Syndrome:
Last update: August 26, 2021
Sea Star Wasting Disease (SSWD) – summary of current state of knowledge
Since 2013, more than twenty species of sea star have been impacted by SSWD from Mexico to Alaska. There is local variation in intensity of the disease and which species are impacted. It is one of the largest wildlife die-off events in recorded history. Sea stars contort, have lesions, shed arms and become piles of decay (see below for photos and detail about the progression of the disease).
There is NOT scientific consensus about the cause. Current hypotheses focus on (i) a virus and (ii) low oxygen at the surface of the sea star’s skin maintained due to bacteria. What is consistent in is that changing environmental conditions appear to allow the pathogen (be it bacteria or viruses) to have a greater impact.
The best current source for a summary of the research is Hamilton et al (August, 2021). From that source: ” . . . outbreak severity may stem from an interaction between disease severity and warmer waters” and “Though we lack a mechanistic understanding of whether temperature or climate change triggered the SSWD outbreak, this study adds to existing evidence that the speed and severity of SSWD are greater in warmer waters”.
As with any pathogen (like the flu virus), the expression of a pathogen as disease is influenced by the number and proximity of individuals i.e. more animals together leads to faster spread of the virus and/or bacteria.
Currently, some species of sea star appear to be recovering while others remain very heavily impacted. Sunflower Stars (Pycnopodia helianthoides) have been devastated and were added to the International Union for Conservation of Nature (IUCN) list as Critically Endangered on December 10th, 2020. There are current efforts to have Sunflower Stars assessed by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) with hopes that they receive protection under Canada’s Species at Risk Act.
See the media release from the Nature Conservancy “Iconic Sea Star Listed Critically Endangered After Study Finds Marine Epidemic Event Nearly Wiped Out Global Population” at this link.
There has been much recent media coverage on how Sunflower Stars are being bred in captivity. While such efforts are of course to be applauded and are part of the research needed to understand / mitigate Sea Star Wasting Syndrome, the inclination of the media to put this forward as the solution is troublesome. If the pathogen causing Sea Star Wasting Syndrome is not known, and the stressors related to climate change continue, releasing these Sunflower Stars into the Ocean would expose them to the same stressors as those who died.
Sunflower Stars are of great ecological importance in maintaining kelp forests.- Research published by Burt et al in 2018 quantifies the importance of Sunflower Stars in maintaining kelp forests. Includes that the decline of Sunflower Stars “corresponded to a 311% increase in medium urchins and a 30% decline in kelp densities”
From Hamilton et al (August, 2021):
“The aetiological agent(s) driving SSWD remain unidentified. Current hypotheses focus on (i) a viral-sized aetiological agent (e.g. sea star-associated densovirus) and (ii) low oxygen at the surface of the skin maintained through subsequent bacterial proliferation [7,15]. Additionally, the relationship between temperature and SSWD is unresolved. In laboratory studies, the lesion growth rate increased with increasing temperature, but evidence for warm temperatures triggering SSWD is mixed [16–18]. Some studies showed a positive relationship between the timing of the outbreak and temperature [6,18,19], while others found no relationship [8,20] or a negative relationship . Differences in disease detection could explain these variable field observations. SSWD is a fast-paced disease accelerating at the scale of weeks to months, so peak prevalence of infection is difficult to detect from seasonal or annual monitoring programmes . Thus, the relationship between environmental triggers of an outbreak can easily be confounded with pandemic disease dynamics  . . . Additionally, whether climate change or warm temperatures triggered the outbreak remains unknown. Harvell et al.  showed that warm temperature anomalies explained more than a third of the variance in Pycnopodia outbreak timing in the Salish Sea . Furthermore, Aalto et al.  modelled the initial outbreak spread dynamics and suggested that warm temperatures can trigger disease and increase mortality . Conversely, several studies found that warmer ocean temperatures were not associated with SSWD outbreak timing in Pisaster ochraceus in Oregon and California [8,21]. Though we lack a mechanistic understanding of whether temperature or climate change triggered the SSWD outbreak, this study adds to existing evidence that the speed and severity of SSWD are greater in warmer waters.”
See the latest research at:
August 2021: Hamilton S. L., Saccomanno V. R., Heady W. N., Gehman A. L., Lonhart S. I., Beas-Luna R., Francis F. T., Lee L., Rogers-Bennett L., Salomon A. K. and Gravem S. A. (2021) Disease-driven mass mortality event leads to widespread extirpation and variable recovery potential of a marine predator across the eastern Pacific. Proc. R. Soc. B.288
June 2021: Jackson, E.W., Wilhelm, R.C., Johnson, M.R., Lutz, H., Danforth, I., Gaydos, J., Hart, M., & Hewson, I. (2020). Diversity of Sea Star-Associated Densoviruses and Transcribed Endogenous Viral Elements of Densovirus Origin. Journal of Virology, 95.
January 2021: Aquino CA, Besemer RM, DeRito CM, Kocian J, Porter IR, Raimondi PT, Rede JE, Schiebelhut LM, Sparks JP, Wares JP and Hewson I (2021) Evidence That Microorganisms at the Animal-Water Interface Drive Sea Star Wasting Disease. Front. Microbiol. 11:610009. doi: 10.3389/fmicb.2020.610009. See Cornell University coverage of this research “Organic matter, bacteria doom sea stars to oxygen depletion”. Also, see further communication from one of the lead researchers, Dr. Ian Hewson, at this link.
November 2020: Hewson, I.; Aquino, C.A.; DeRito, C.M. Virome Variation during Sea Star Wasting Disease Progression in Pisaster ochraceus (Asteroidea, Echinodermata). Viruses 2020, 12, 1332.
Why share this information? It is often marine species that testify to environmental problems first, serving as indicators for the resources upon which we too depend. The hypothesis remains that the sea stars have succumbed in an unprecedented way because of changed ocean conditions (stressors). Too few of us realize the importance of sea stars in the ocean food web (see video below) let alone the importance of what they might be indicated about environmental health.
Below, January 30, 2019 video by the Hakai Institute re. Sunflower Stars and Sea Star Wasting Disease.
Further detail on recent research
Research published on January 6th, 2021 (Aquino et al) suggests that the pathogen is not a virus but a bacteria but, again, there is not scientific consensus about this. The research puts forward that warmer oceans and increased organic matter appear to lead to increases in specific bacteria (copiotrophs) that then use up the oxygen at the interface of the sea star and the bacteria, and the sea stars can’t breathe. The hypothesis includes that “more heavily affected species were rougher and therefore had a much larger boundary layer (the layer at the animal-water interface) than those species which were less affected.”
October 21, 2019 – Research by Rogers-Bennet and Catton published in Scientific Reports on Bull Kelp deforestation off the coast of Northern California – Marine heat wave and multiple stressors tip bull kelp forest to sea urchin barrens. Abstract: “Extreme climatic events have recently impacted marine ecosystems around the world, including foundation species such as corals and kelps. Here, we describe the rapid climate-driven catastrophic shift in 2014 from a previously robust kelp forest to unproductive large scale urchin barrens in northern California. Bull kelp canopy was reduced by >90% along more than 350 km of coastline. Twenty years of kelp ecosystem surveys reveal the timing and magnitude of events, including mass mortalities of sea stars (2013-), intense ocean warming (2014–2017), and sea urchin barrens (2015-). Multiple stressors led to the unprecedented and long-lasting decline of the kelp forest. Kelp deforestation triggered mass (80%) abalone mortality (2017) resulting in the closure in 2018 of the recreational abalone fishery worth an estimated $44 M and the collapse of the north coast commercial red sea urchin fishery (2015-) worth $3 M. Key questions remain such as the relative roles of ocean warming and sea star disease in the massive purple sea urchin population increase. Science and policy will need to partner to better understand drivers, build climate-resilient fisheries and kelp forest recovery strategies in order to restore essential kelp forest ecosystem services.”
January 30, 2019 – Paper published in Science Advances by Harvell et al – Disease epidemic and a marine heat wave are associated with the continental-scale collapse of a pivotal predator (Pycnopodia helianthoides). Quote from lead author: “The main takeaway is the speed with which a multi-host infectious disease can cause decline in the most susceptible host [Sunflower Stars] and that warming temperatures can field bigger impacts of disease outbreaks.” Abstract includes: “Since 2013, a sea star wasting disease has affected >20 sea star species from Mexico to Alaska. The common, predatory sunflower star (Pycnopodia helianthoides), shown to be highly susceptible to sea star wasting disease, has been extirpated across most of its range. Diver surveys conducted in shallow nearshore waters (n = 10,956; 2006–2017) from California to Alaska and deep offshore (55 to 1280 m) trawl surveys from California to Washington (n = 8968; 2004–2016) reveal 80 to 100% declines across a ~3000-km range. Furthermore, timing of peak declines in nearshore waters coincided with anomalously warm sea surface temperatures. The rapid, widespread decline of this pivotal subtidal predator threatens its persistence and may have large ecosystem-level consequences.”
The paper’s discussion includes: “Cascading effects of the P. helianthoides loss are expected across its range and will likely change the shallow water seascape in some locations and threaten biodiversity through the indirect loss of kelp. P. helianthoides was the highest biomass subtidal asteroid across most of its range before the Northeast Pacific SSWD event. Loss or absence of this major predator has already been associated with elevated densities of green (Strongylocentrotus droebachiensis), red (Mesocentrotus franciscanus), and purple urchins (Strongylocentrotus purpuratus) across their range, even in regions with multiple urchin predators. Associated kelp reductions have been reported following the outbreak . . . SSWD, the anomalously warm water, P. helianthoides declines, and subsequent urchin explosions . . . have been described as the “perfect storm.” This “storm” could result not only in trophic cascades and reduced kelp beds but also in abalone and urchin starvation.”
July 2018 – Research published by Burt et al) quantifies the importance of Sunflower Stars in maintaining kelp forests. Includes that the decline of Sunflower Stars “corresponded to a 311% increase in medium urchins and a 30% decline in kelp densities”. See news coverage on the research at this link.
March 7, 2018 – Additional research by Hewsen et al has found that, while a virus appears associated with the disease in Sunflower Stars, the situation is more complex and the virus does not appear to be the cause in other sea star species. The cause is “likely a complex tango of diverse potential pathogens and environmental conditions” / “We speculate that SSWD may represent a syndrome of heterogeneous etiologies [causes] between geographic locations, between species, or even within a species between locations.” Those considered in the paper in addition to viruses: Drought / excessive rainfall; freshwater toxins (transmitted by excessive rainfall post drought); temperature swings.
This does not let climate change off the hook. Quote by lead author: “Since some of those disease causes may include swings in temperature or precipitation, ultimately which may be related to climate change, we need to focus our efforts on remediating climate change . . ”
The paper suggests renaming the wasting disease to Asteroid Idiopathic Wasting Syndrome because the term correlates with an array of symptoms, “which is more correct for describing this situation, as there are likely multiple diseases present . . .”
Green Urchins grazing on Split Kelp. ©Jackie Hildering.
Research published in June 2018 (Schiebelhut et al), specifically on Ochre Stars, found that the genetic makeup of the species has changed since the outbreak. Young Ochre Sea Stars are more similar genetically to adults who survived than to those who succumbed. This “may influence the resilience of this keystone species to future outbreaks”. The findings of an additional March 2018 paper (Miner et al) include ” . . . we documented higher recruitment of P. ochraceus [Ochre Stars] in the north than in the south, and while some juveniles are surviving (as evidenced by transition of recruitment pulses to larger size classes), post-SSWD survivorship is lower than during pre-SSWD periods.
Sources for the above:
- Burt JM, Tinker MT, Okamoto DK, Demes KW, Holmes K, Salomon AK (2018) Sudden collapse of a mesopredator reveals its complementary role in mediating rocky reef regime shifts. Proceedings of the Royal Society B 285(1883): 20180553.
- Hewson I, Bistolas KSI, Quijano Cardé EM, Button JB, Foster PJ, Flanzenbaum JM, Kocian J and Lewis CK (2018) Investigating the Complex Association Between Viral Ecology, Environment, and Northeast Pacific Sea Star Wasting. Front. Mar. Sci. 5:77. doi: 10.3389/fmars.2018.00077
- Schiebelhut, Lauren (2018), Supporting Files for Schiebelhut LM, Puritz JB & Dawson MN (2018) Decimation by sea star wasting disease and rapid genetic change in a keystone species, Pisaster ochraceus PNAS, UC Merced Dash, Dataset.
- Cornell Chronicle, Scientists unravel complex factors of starfish diseases.
- Miner CM, Burnaford JL, Ambrose RF, Antrim L, Bohlmann H, Blanchette CA, et al. (2018) Large-scale impacts of sea star wasting disease (SSWD) on intertidal sea stars and implications for recovery. PLoS ONE 13(3): e0192870. https://doi.org/10.1371/journal.pone.0192870
Fom my original blog November 10, 2013:
There has already been much reporting on the gruesome epidemic spreading like wildfire through several species of sea star in the NE Pacific Ocean.
“Sea star wasting syndrome” is incredibly virulent and is causing the mass mortality of some sea star species in British Columbia and beyond. “Sea stars go from “appearing normal” to becoming a pile of white bacteria and scattered skeletal bits is only a matter of a couple of weeks, possibly less than that” (Source #1).
What I have strived to do is bundle the state of knowledge so far, relying heavily on the expertise of two extraordinary divers and marine naturalists: (1) Neil McDaniel, marine zoologist and underwater photographer / videographer who maintains a website on local sea stars and has put together A Field Guide to Sea Stars of the Pacific Northwest, and (2) Andy Lamb, whose books include Marine Life of the Pacific Northwest.
I am hoping that kayakers, beach-walkers and fellow divers will help monitor and report on the spread of the disease but I am also hoping that all of us may learn from this tragedy that has impacted “one of the most iconic animals on the coast of British Columbia . . . more abundant and diverse in our waters than anywhere else in the world” (Source #3).
Sea Star Wasting Syndrome reminds us of the fragility of ocean ecosystems; how very quickly disease could spread in the ocean; and how we are all empowered to reduce stressors that increase the likelihood of pathogens manifesting as disease (e.g. climate change) or even that pathogens enter the environment (e.g. sewage).
High mortalities (note that the first 4 are members of the same family – the Asteriidae):
- Sunflower star (Pycnopodia helianthoides) hardest hit in southern British Columbia. From communication with Neil McDaniel ” . . .so far I estimate it has killed tens, possibly hundreds of thousands of Pycnopodia in British Columbia waters.”
- Mottled star (Evasterias troschelii)
- Giant pink star (Pisaster brevispinus)
- Ochre star aka purple star (Pisaster ochraceus)
- Morning sun star (Solaster dawsoni)
More limited mortalities:
- Vermillion star (Mediaster aequalis); video of an afflicted star here.
- Rainbow star (Orthasterias koehleri)
- Leather star (Dermasterias imbricata)
- Striped sun star (Solaster stimpsoni)
- Six-rayed stars (Leptasterias sp.)
Update January 21st, 2014: Possibly: Rose star (Crossaster papposus) – I have noted symptoms in this species on NE Vancouver Island as has Neil McDaniel in S. British Columbia).
Symptoms and progression of SSWD:
Neil McDaniel shared the following 7 images for the progression of the disease in Sunflower Stars [Source #2 and #14]. See the end of this blog item for images showing symptoms in other sea star species as well as a 1 minute time-lapse clip showing the progression of the syndrome in a Sunflower Star over 7 hours. [Note that the progression of the Syndrome on NE Vancouver Island appears that it may be different from what has been observed further to the south.]
1. In this image most of the Sunflower Stars appear healthy “other than one just right of center frame is exhibiting the syndrome, looking “thinned-out” and emaciated.”
2. This images “shows this thinning in close-up. Note how distinct the edges of the rays look and how flat the star is.”
3. This image “shows how the body wall begins to rupture, allowing the gonads and pyloric caeca to spill out.”
As the animals become more stressed, they often drop several rays (which wander off on their own for a while). At this point the body wall becomes compromised and the pyloric caeca and/or gonads may protrude through lesions. As things progress, the animals lose the ability to crawl and may even tumble down steep slopes and end up in pile at the bottom. Soon after they die and begin to rot
4. This image “shows the gonads breaking through holes in the body wall. At this point rays often break off and crawl away briefly.”
5. As things progress, the animals lose the ability to crawl [and hold grip surfaces] and may even tumble down steep slopes and end up in pile at the bottom. Soon after they die and begin to rot.
6. The bacteria Beggiatoa then takes over and consumes all of the organic matter, leaving a scattering of skeletal plates on the bottom. The syndrome develops quickly and in only one to two weeks animals can go from appearing healthy to a white mat of bacteria and skeletal plates
7. This image “shows an individual star that is being consumed by mat bacteria.”
The 1-minute time-lapse video below shows the progression of the Syndrome in a sunflower star over 7 hours.
To date, the cause(s) have not yet been identified. Scientific opinion appears to be that most likely the cause is one or more viruses or bacteria. As with any pathogen (like the flu virus), the expression of a pathogen as disease is influenced by the number and proximity of individuals and could be exacerbated by environmental stressors.
Using cutting-edge DNA sequencing and metagenomics, Hewson is analyzing the samples for viruses as well as bacteria and other protozoa in order to pinpoint the infectious agent among countless possibilities.
“It’s like the matrix,” Hewson said. “We have to be very careful that we’re not identifying something that’s associated with the disease but not the cause.”
- ”In previous outbreaks the “proximal cause” was found to a vibrio bacterium but “a recent wasting event on the east coast of the United States has been attributed to a virus . . . such events are often associated with warmer than typical water temperatures . . . Please note that we do not know what is causing Sea Star Wasting Syndrome, and the cause may be different in different regions . . . the period prior to Wasting was characterized by warm water temperatures” (University of California Santa Cruz, Source #4).
- Bates et al reported on an outbreak of wasting syndrome in ochre stars in Barkley sound in 2008. This included conducting lab experiments finding that the “prevalence and infection intensity were always higher in warm temperature treatments” and that “small increases in temperature could drive mass mortalities of Pisaster [ochre stars] due to wasting disease.” [Source #13 and #14]
- “Do not believe this is related to a warming trend” (Source #18).
- “Overpopulation” of sunflower stars appears to be a factor with outbreaks occurring where there is a high abundance of sea stars. “Often when you have a population explosion of any species you end up with a disease outbreak” (Source #5). “This could be perfectly normal as a way to control overpopulation” (Source #18).
- “Some initial samples sent to DFO [Department of Fisheries and Oceans] and UBC [University of British Columbia] have not isolated a specific causative agent for this sea star die off. More samples are being collected and additional tests will be conducted” (Source #2 and #7). Viruses are notoriously difficult to detect. Cornell University (New York) has begun viral and bacterial culturing (Source #8). Updates will be provided here as they become available. See Source #14 for the results of pathology reports from October 4, November 12 and November 13.
- Quote from Drew Harvell, a Cornell University professor of ecology and evolutionary biology who studies marine diseases: “these kinds of events are sentinels of change. When you get an event like this, I think everybody will say it’s an extreme event and it’s pretty important to figure out what’s going on . . . Not knowing is scary . . . If a similar thing were happening to humans, the Centers for Disease Control and Prevention would commit an army of doctors and scientists to unraveling the mystery.” (Source #12)
- Fukushima is a contributing factor?! There is no data to date to support this and, while of course radiation benefits nothing, I worry that pointing the finger away from ourselves takes away from the opportunity to recognize and act on how we all contribute to ocean stressors such as increasing temperature. From Source #19 – “scientists see Fukushima as an unlikely culprit because the die-offs are patchy, popping up in certain places like Seattle and Santa Barbara and not in others, such as coastal Oregon, where wasting has only been reported at one location.”
- Ballast water? “From Source #19- “Others have wondered if a pathogen from the other side of the world may have hitched a ride in the ballast water of ocean-going ships. Scientists say this fits with the fact that many of the hot spots have appeared along major shipping routes. However, the starfish in quiet Monterey Bay, Calif. have been hit hard, whereas San Francisco’s starfish are holding strong.”
Has this happened before?
Never to this large a scale. “Although similar sea star wasting events have occurred previously, a mortality event of this magnitude, with such broad geographic reach has never before been documented.” (Source #17).
- “Southern California in 1983-1984 and again (on a lesser scale) in 1997-98” (Source #4 and #13)
- Florida (Source #5).
- Update November 30: Sunflower die offs [on much smaller scale] have been noted in the past in Barkley Sound. In 2008 ochre star die offs were documented in Barkley Sound. In 2009 Bates et. al. reported on this and observed that the prevalence of disease “was highly temperature sensitive and that populations in sheltered bays appeared to sustain chronic, low levels of infection.” (Source #14 and #15).
- “Similar events have occurred elsewhere over the last 30 years. Sea stars have perished in alarming numbers in Mexico, California and other localities” (Source #2).
- “In July, researchers at the University of Rhode Island reported that sea stars were dying in a similar way from New Jersey to Maine . . a graduate student collected starfish for a research project and then watched as they “appeared to melt” in her tank” (Source #5).
- Email communication with Neil McDaniel.
- Email communication with Andy Lamb.
- Shellfish Health Report from the Pacific Biological Station (DFO) conducted on 1 morning sun star and 7 sunflower stars collected on October 9, 2013 at Croker Island, Indian Arm; case number 8361.
- Email communication with Jeff Marliave.
- Sea star wasting syndrome, Nov 30-13; https://jackiehildering.files.wordpress.com/2013/11/sea-star-wasting-syndrome-nov-30-13.pdf
- Bates AE, Hilton BJ, Harley, CDG 2009. Effects of temperature, season and locality on wasting disease in the keystone predatory sea star Pisaster ochraceus. Diseases of Aquatic Organisms Vol. 86:245-251 http://www.ncbi.nlm.nih.gov/pubmed/20066959
- Video showing impacts in Elliott Bay, Seattle http://earthfix.info/flora-and-fauna/article/sea-stars-dying-off-west-seattle/
- University of California, Santa Cruz Press Release; December 22, 2013; Unprecedented Sea Star Mass Mortality Along the West Coast of North America due to Wasting Syndrome
- Vancouver Aquarium; January 21, 2014; Presentation – Mass Dying of Seastars in Howe Sound and Vancouver Harbour (Dr. Jeff Marliave and Dr. Marty Haulena).
- Earth Fix; January 30, 2014; Northwests starfish experiment gives scientists clues to mysterious mass die-offs
Images showing symptoms in other sea star species: