Sea star wasting disease
Sea star wasting disease or starfish wasting syndrome is a disease of starfish and several other echinoderms that appears sporadically, causing mass mortality of those affected. There are around 40 different species of sea stars that have been affected by this disease. The disease seems to be associated with raised water temperatures in some places, but not others. It starts with the emergence of lesions, followed by body fragmentation and death. In 2014 it was suggested that the disease is associated with a densovirus now known as the sea star-associated densovirus (SSaDV); however, sea star wasting disease is still not fully understood.
Typically the first symptom of sea star wasting disease is refusal to accept food followed by listlessness for weeks and then white lesions that appear on the surface of the starfish and spread rapidly, followed by decay of tissue surrounding the lesions. Next the animal becomes limp as the water vascular system fails and it is no longer able to maintain its internal hydrostatic balance. The sea star loses its grip on the substrate. The body structure begins to break down, signs of stretching appear between the arms which may twist and fall off, and the animal dies. The arms may continue to crawl around for a while after being shed. Progression of these events can be rapid, leading to death within a few days.
A deflated appearance can precede other morphological signs of the disease. All of these symptoms are also associated with ordinary attributes of unhealthy stars and can arise when an individual is stranded too high in the intertidal zone (for example) and simply desiccates. "True" wasting disease will be present in individuals that are found in suitable habitat, often in the midst of other individuals that might also be affected.
The final result is a disintegrated, white, mushy blob, which no longer seems to be a sea star.
The 1972 plague was the first notable case of Sea Star Wasting Disease. Scientists noticed a rapidly declining population of common starfish (Asterias rubens) occurring off the east coast of the United States. The symptoms were that the starfish became limp and lost limbs until finally melting into a white mucus like paste.
In 1978 large numbers of the predatory starfish Heliaster kubiniji succumbed to a wasting disease in the Gulf of California. At the time it was suspected that high water temperatures were a causal factor. This starfish became locally extinct in some parts of the gulf and some populations had still not recovered by the year 2000. Because this starfish is a top-level predator, its disappearance had profound effects on the ecosystem. In the Channel Islands off the coast of California, ten species of sea star were recorded as being affected as well as three species of sea urchins, two brittle stars and a sea cucumber, all of which experienced large population declines.
2013 - Current Plagues
In July 2013, populations of sea stars declined rapidly on the east coast of the United States between New Jersey and Maine. There had been a great increase in sea star numbers three years earlier, though in 2013 they were dying off. No cause for the mysterious deaths was apparent. On the Pacific coast, a meltdown of sea stars was first found in ochre stars and sunflower stars in Howe Sound, British Columbia. In late August, the disease had also been found stretching from Alaska to the border of Mexico.
At the beginning of September 2013, a mass die-off of sea stars was reported off the coast of British Columbia. The sea bed was littered with disintegrating sunflower stars (Pycnopodia helianthoides), their detached arms and discs. Another species also suffering mortalities was the morning sun star (Solaster dawsoni), but no cause for the deaths was apparent. If they were caused by infection or toxins, the two species might have affected each other because the diet of each includes sea stars.
In spring/summer 2013, reports of sea stars experiencing wasting symptoms came from Vancouver, B.C. and from southern and central California. Observations of symptoms spread throughout California, Washington and southern Canada throughout 2013, but sea star wasting disease did not begin affecting sea stars in the intertidal zone in Oregon until spring 2014. The relatively high resolution of understanding of the pattern of disease spread came from marine scientists working along the coast, but also from citizen scientists visiting the coast and uploading their observations, of where they saw sea stars both with and without disease symptoms, to an online sea star wasting observation log database.
Because scientists had been studying sea star populations before the outbreak of sea star wasting disease, there is a good understanding of how the disease affected population sizes and dynamics. A study of the ochre sea star (Pisaster ochraceus) populations from San Diego, California, to southern British Columbia, along with at two locations near Sitka, Alaska, found that population declines were proportionately greater for sea stars in the southern part of the coast than the north; however, population numbers are usually higher at more northern locations, so the number of sea stars that died from wasting disease was often higher at more northern sites.
In October 2013, in a marine laboratory seawater tank in California holding various species of sea stars, other species started displaying similar symptoms. The ochre star (Pisaster ochraceus) was the first affected. Most of these developed symptoms, lost arms and died over the course of a week or so. Later the rainbow star (Orthasterias koehleri) developed the disease and died, but the bat star (Patiria miniata) and leather star (Dermasterias imbricata), which were living in the same tank and had been scavenging on the corpses, showed no ill effects. At Natural Bridges State Marine Reserve in California, the ochre star is normally a very common resident on the mussel beds, but by November 2013 it was reported to have completely disappeared.
There have been signs of some recovery of ochre sea star populations (Pisaster ochraceus), with higher numbers of juvenile sea stars in the intertidal than had been previously common, especially for northern sites along the Pacific coast. However, the biomass and the function of ochre sea stars in their communities, such as being important predators of mussels, has remained lower than pre-disease levels.
As of November 2013, no identifiable cause for the disease had been found. Pathogenic bacteria did not seem to be present, and though the plague might be caused by a viral or fungal pathogen, no causal agent had been found. Each episode of plague might have a different cause.
Other possible causes of the condition that have been suggested include high sea temperatures, oxygen depletion and low salinity due to freshwater runoff. Research suggests that high water temperatures can be indeed linked to the disease, increasing its incidence and virulence. The disease also seems more prevalent in sheltered waters than in open seas with much wave movement. One result of global warming is higher sea temperatures. There is a wave of unusually warm water along the west coast of the United States, which is where all of the sea stars are dying off. These may impact both on starfish and on echinoderm populations in general, and a ciliate protozoan parasite (Orchitophrya stellarum) of starfish, which eats sperm and effectively emasculates male starfish, thrives at higher temperatures. However, temperature was not related to the initial outbreak of sea star wasting disease at many places along the coast. Unlike with many other wildlife diseases, there was no link between the density of sea stars at a location before disease outbreak and the severity of population decline. Thus, this outbreak has defied prediction using what is typically understood about disease spread.
Research in 2014 showed that the cause of the disease is transmissible from one starfish to another and that the disease-causing agent is a microorganism in the virus-size range. The most likely candidate causal agent was found to be the sea star-associated densovirus (SSaDV), which was found to be in greater abundance in diseased starfish than in healthy ones. However, evidence for this virus as the cause of sea star wasting disease is inconclusive.
In 2014, Point Defiance Zoo and Aquarium lost more than half of its 369 sea stars, and by September 2015 they numbered fewer than 100. The aquarium treated its affected sea stars with antibiotics in 2014, which proved effective. Although a mechanism is still unknown, evidence suggests that a single mutation in the elongation factor 1-alpha locus in Pisaster ochraceus may be associated with reduced mortality.
Most affected (high mortality rates):
- Solaster dawsoni (morning sun star),
- Pisaster brevispinus (giant pink star),
- Pisaster ochraceus (ochre/purple star),
- Pycnopodia helianthoides (sunflower star),
- Evasterias troschelii (mottled star),
Affected (some mortality):
- Dermasterias imbricata (leather star),
- Solaster stimpsoni (striped sun star),
- Orthasterias koehleri (rainbow star),
- Henricia spp. (blood star),
- Leptasterias spp (six-armed star),
- Patiria (Asterina) miniata (bat star), and
- Pisaster giganteus (giant star)
- Dawsoni, Solaster. "Sea Star Species Affected by Wasting Syndrome." Pacificrockyintertidal.org Seastarwasting.org (n.d.): n. pag. Ecology and Evolutionary Biology. Web.
- Eisenlord, Morgan E.; Groner, Maya L.; Yoshioka, Reyn M.; Elliott, Joel; Maynard, Jeffrey; Fradkin, Steven; Turner, Margaret; Pyne, Katie; Rivlin, Natalie (2016-03-05). "Ochre star mortality during the 2014 wasting disease epizootic: role of population size structure and temperature". Phil. Trans. R. Soc. B. 371 (1689): 20150212. doi:10.1098/rstb.2015.0212. ISSN 0962-8436. PMC 4760142. PMID 26880844.
- Bates, Amanda E.; Hilton, Brett J.; Harley, Christopher D. G. (2009-11-09). "Effects of temperature, season and locality on wasting disease in the keystone predatory sea star Pisaster ochraceus". Diseases of Aquatic Organisms. 86 (3): 245–251. doi:10.3354/dao02125. ISSN 0177-5103. PMID 20066959.
- Menge, Bruce A.; Cerny-Chipman, Elizabeth B.; Johnson, Angela; Sullivan, Jenna; Gravem, Sarah; Chan, Francis (2016-05-04). "Sea Star Wasting Disease in the Keystone Predator Pisaster ochraceus in Oregon: Insights into Differential Population Impacts, Recovery, Predation Rate, and Temperature Effects from Long-Term Research". PLOS ONE. 11 (5): e0153994. doi:10.1371/journal.pone.0153994. ISSN 1932-6203. PMC 4856327. PMID 27144391.
- Miner, C. Melissa; Burnaford, Jennifer L.; Ambrose, Richard F.; Antrim, Liam; Bohlmann, Heath; Blanchette, Carol A.; Engle, John M.; Fradkin, Steven C.; Gaddam, Rani (2018-03-20). "Large-scale impacts of sea star wasting disease (SSWD) on intertidal sea stars and implications for recovery". PLOS ONE. 13 (3): e0192870. doi:10.1371/journal.pone.0192870. ISSN 1932-6203. PMC 5860697. PMID 29558484.
- "Sea Star Wasting Syndrome". Pacific Rocky Intertidal Monitoring. Retrieved 2014-02-01.
- Hewson, Ian; et al. (2014). "Densovirus associated with sea-star wasting disease and mass mortality". Proceedings of the National Academy of Sciences of the United States of America. 111 (48): 17278–83. doi:10.1073/pnas.1416625111. PMC 4260605. PMID 25404293.
- "Sea Star Wasting Syndrome | MARINe". eeb.ucsc.edu. Retrieved 2018-06-03.
- Gong, Allison J. (2013-09-07). "A plague of stars". Notes from a California naturalist. Retrieved 2013-11-17.
- "Sea Star Wasting Syndrome". Pacific Rocky Intertidal Monitoring: Trends and Synthesis. Retrieved 2014-02-03.
- Meyer, Anna. "Will the Sea Stars Ever Be Able to Recover? - Islands' Sounder." Islands' Sounder. N.p., 20 July 2015. Web. 08 Oct. 2015.
- Menge, Bruce A. (August 1979). "Coexistence between the seastars Asterias vulgaris and A. forbesi in a heterogeneous environment: A non-equilibrium explanation". Oecologia. 41 (3): 245–272. doi:10.1007/bf00377430. ISSN 0029-8549. PMID 28309763.
- Mah, Christopher (2013-09-10). "Starfish Wasting Disease!". Echinoblog. Retrieved 2013-11-17.
- Dungan, Michael L.; Miller, Thomas E.; Thomson, Donald A. (1982). "Catastrophic Decline of a Top Carnivore in the Gulf of California Rocky Intertidal Zone". Science. 216 (4549): 989–991. doi:10.1126/science.216.4549.989. PMID 17809070.
- Eckert, Ginny L.; Engle, John M.; Kushner, David J. (2000). "Sea star disease and population declines at the Channel Islands" (PDF). Proceedings of the Fifth California Islands Symposium. Minerals Management Service 99-0038: 390–393.
- Laine, Martin (2013-07-24). "Massive east coast starfish die-off reported". Digital Journal. Retrieved 2013-11-17.
- "Sea Star Wasting Syndrome Now Documented on NE Vancouver Island." http://themarinedetective.com/2013/12/21/sea-star-wasting-syndrome-now-documented-on-ne-vancouver-island/
- Mah, Christopher (2013-09-03). "Mysterious Mass Sunflower Starfish (Pycnopodia) Die-off in British Columbia". Echinoblog. Retrieved 2013-11-17.
- "Pacific Rocky Intertidal Monitoring". data.piscoweb.org. Retrieved 2018-11-27.
- "MARINe Sea Star Logs". gordon.science.oregonstate.edu. Retrieved 2018-11-27.
- Moritsch, Monica M.; Raimondi, Peter T. (2018-03-23). "Reduction and recovery of keystone predation pressure after disease-related mass mortality". Ecology and Evolution. 8 (8): 3952–3964. doi:10.1002/ece3.3953. ISSN 2045-7758. PMC 5916292. PMID 29721271.
- "Pacific Rocky Intertidal Monitoring: Trends and Synthesis." Pacific Rocky Intertidal Monitoring. N.p., n.d. Web. 08 Oct. 2015.
- "'Warm Blob' of Water Causing Extreme Weather, Climate Scientists Say". The Weather Channel. Retrieved 2015-10-10.
- Mah, Christopher (2010-07-20). "Another Worry From Global Warming: Parasites that eat Starfish Sperm". Echinoblog. Retrieved 2013-11-17.
- Netburn, Deborah (November 26, 2014) "Scientists find likely culprit behind mysterious sea star deaths" Los Angeles Times
- Glenn, Stacia. "Point Defiance loses half its sea stars to a wasting disease." http://www.thenewstribune.com/news/local/article34291203.html
- Wares, J. P. and L. M. Schiebelhut, 2016. PeerJ 4:e1876 https://peerj.com/articles/1876/?td=wk
- Dawsoni, Solaster. Pacificrockyintertidal.org Seastarwasting.org (n.d.): n. pag. Web.
- Glenn, Stacia. "Point Defiance Loses Half Its Sea Stars to a Wasting Aquatic Disease." Thenewstribune. N.p., 07 Sept. 2015. Web. 08 Oct. 2015.