Magnificent star, a member of Paxillosida. Credit: Dr. Dwayne Meadows, NOAA/NMFS/OPR Since 2013, millions of sea stars native to the Pacific coast of North America from Baja California to southern Alaska have succumbed to a mysterious wasting disease in which their limbs pull away from their bodies and their organs exude through their skin; a disease researchers say could trigger an unprecedented ecological upheaval under the waves. 
 
 Now, a researcher in the College of Agriculture and Life Sciences has identified the deadly culprit as the Sea Star Associated Densovirus (SSaDV), a type of parvovirus commonly found in invertebrates. In a study published Nov. 17 in the Proceedings of the National Academy of Sciences, Hewson and colleagues present a genomic analysis of the newly discovered virus prevalent in symptomatic sea stars. 
 
 "There are 10 million viruses in a drop of seawater, so discovering the virus associated with a marine disease can be like looking for a needle in a haystack," says lead author Ian Hewson, a professor of microbiology. "Not only is this an important discovery of a virus involved in a mass mortality of marine invertebrates, but this is also the first virus described in a sea star." 
 
 Hewson suggests that the virus has been smoldering at a low level for many years. It was present in museum samples of sea stars collected in 1942, 1980, 1987 and 1991, and may have risen to epidemic levels in the last few years due to sea star overpopulation, environmental changes, or mutation of the virus. Sea water, plankton, sediments and water filters from public aquariums, sea urchins and brittle stars also harbored the virus. 
 
 The research lays the groundwork for understanding how the virus kills sea stars and what triggers outbreaks. The stakes are high, according to Drew Harvell, a professor of ecology and evolutionary biology and a co-author on the paper. As voracious predators on the ocean floor, sea stars are 'keystone' species which have a large role in maintaining diversity in their ecosystem. 
 
 Lead researcher Ian Hewson describes Densovirus. Credit: Cornell University "It's the experiment of the century for marine ecologists," said Harvell. "It is happening at such a large scale to the most important predators of the tidal and sub-tidal zones. Their disappearance is an experiment in ecological upheaval the likes of which we've never seen." 
 
 Both the National Science Foundation (NSF) and Cornell University's David R. Atkinson Center for a Sustainable Future provided rapid response funds to Hewson and his co-principal investigator Ben Miner, Western Washington University. 
 
 "The recent outbreak of sea star wasting disease on the U.S. West Coast has been a concern for coastal residents and marine ecologists," said David Garrison, program director in the NSF's Division of Ocean Sciences. "This study, supported as a rapid response award, has made a significant contribution to understanding the disease." 
 
 Explore further: Sea star wasting devastates Pacific Coast species 
 
 More information: Densovirus associated with sea-star wasting disease and mass mortality, PNAS, www.pnas.org/cgi/doi/10.1073/pnas.1416625111 
 
 ||||| Sea stars inhabiting the Northeast Pacific Coast have recently experienced an extensive outbreak of wasting disease, leading to their degradation and disappearance from many coastal areas. In this paper, we present evidence that the cause of the disease is transmissible from disease-affected animals to apparently healthy individuals, that the disease-causing agent is a virus-sized microorganism, and that the best candidate viral taxon, the sea star-associated densovirus (SSaDV), is in greater abundance in diseased than in healthy sea stars. 
 
 Abstract 
 
 Populations of at least 20 asteroid species on the Northeast Pacific Coast have recently experienced an extensive outbreak of sea-star (asteroid) wasting disease (SSWD). The disease leads to behavioral changes, lesions, loss of turgor, limb autotomy, and death characterized by rapid degradation (“melting”). Here, we present evidence from experimental challenge studies and field observations that link the mass mortalities to a densovirus (Parvoviridae). Virus-sized material (i.e., <0.2 μm) from symptomatic tissues that was inoculated into asymptomatic asteroids consistently resulted in SSWD signs whereas animals receiving heat-killed (i.e., control) virus-sized inoculum remained asymptomatic. Viral metagenomic investigations revealed the sea star-associated densovirus (SSaDV) as the most likely candidate virus associated with tissues from symptomatic asteroids. Quantification of SSaDV during transmission trials indicated that progression of SSWD paralleled increased SSaDV load. In field surveys, SSaDV loads were more abundant in symptomatic than in asymptomatic asteroids. SSaDV could be detected in plankton, sediments and in nonasteroid echinoderms, providing a possible mechanism for viral spread. SSaDV was detected in museum specimens of asteroids from 1942, suggesting that it has been present on the North American Pacific Coast for at least 72 y. SSaDV is therefore the most promising candidate disease agent responsible for asteroid mass mortality. ||||| This diseased ochre star was found at Davenport Landing, north of Santa Cruz, Calif. Sea star wasting disease causes lesions to form on the body and legs, which eventually lead to tissue decay and death. 
 
 It starts with the curling of a limb — just a subtle hint that the sea star's body isn't behaving the way it should. Then all the limbs join in, twisting themselves into a pretzel shape until they fall off altogether. By the time the disease has run its course, there's nothing left of the infected animal but a gooey lump of decomposing flesh. 
 
 While this may seem like the premise of a zombie movie, it's actually a description of starfish wasting syndrome — a real disease that is killing off one of the sea's most iconic invertebrates. While the disease has affected starfish (also known as sea stars) for decades, scientists have long puzzled over what might be causing it. Now, one group of researchers may finally have the answer. 
 
 The disease is most likely caused by a virus, according to the researchers, who represent a number of institutions, including Cornell University and the University of California, Santa Cruz. Specifically, the scientists have linked the disease to a densovirus (Parvoviridae), which currently affects at least 20 species of starfish on the Pacific coast of North America. [In Photos: Sick Sea Stars Turn to Goo] 
 
 Star detectives 
 
 Starfish wasting disease was first identified in 1979, but since then, no one has been able to pin down a precise cause, according to Pete Raimondi, a professor of ecology and evolutionary biology at UC Santa Cruz and co-author of the new sea star study. Scientists long believed that outbreaks of the disease — which occurred in 1983, 1998 and most recently starting in 2013 — may be linked to environmental stressors, such as spikes in ocean temperature or pollution from shipping lanes and marinas, Raimondi told Live Science. 
 
 But while such stressors may have something to do with the rapid spread of sea star wasting syndrome, the researchers now think the underlying cause of the disease is the waterborne densovirus. 
 
 "What convinced me that this was an infectious agent was that sea stars that had been in captivity in public aquariums for 30 years suddenly died," said Ian Hewson, an associate professor of microbiology at Cornell and lead author of the study. "There was good evidence that it was something coming in through the intake for the aquariums that wasn't being removed by the sand filtration. And [aquariums] receiving UV-treated water weren't getting sick." 
 
 To test this hypothesis, Hewson and his team used a process known as metagenomics, in which genetic material is collected directly from environmental samples and then sequenced in a lab. The researchers collected tissue samples from both healthy starfish and those affected by the wasting disease. They then extracted DNA from these samples and tried to figure out how the healthy tissue differed from the infected tissue. The difference between the two kinds of samples soon became clear: the infected tissue contained a densovirus, Hewson said. [5 Mysterious Animal Die-Offs] 
 
 "Armed with that knowledge, we went out and tried to understand whether the association between the disease and the densovirus was robust," Hewson told Live Science. Aided by Raimondi and other scientists on the West Coast, the researchers collected 465 healthy and diseased sea stars, he added. 
 
 With sea stars in hand, the researchers determined which of the animals were infected with the virus. They then measured how much of the virus was present in the animal's tissue per unit of weight— a measurement known as viral load. Ultimately, they found a significant association between the presence of the disease and the abundance of the viral tissue, according to Hewson. The researchers believe this association supports their hypothesis that the wasting disease is caused by the sea-star associated densovirus. 
 
 In addition to these tests, the researchers infected some healthy sea stars with the densovirus, and the animals became sick within 7 to 10 days, Hewson said. 
 
 "What we're dealing with are animals that are crawling with bacteria and other microorganisms. Trying to prove beyond a reasonable doubt that any specific virus is responsible for the disease is a really big challenge because you can't isolate it away from those native bacteria. But our evidence is very strong that it’s a sea star associated densovirus," Hewson said, 
 
 Ongoing observations 
 
 Now that scientists have an idea about what may be causing the biggest sea star plague in history, they can start focusing on how the virus attacks the sea star's tissues and what might be triggering outbreaks. 
 
 "An avenue of research that we're really going to have to pursue is how much of a reservoir effect is there in the system," said Raimondi, who notes that it's possible other species are playing host to the virus between outbreaks. 
 
 The researchers are also hoping to keep studying the ecological effects of the disease, according to Hewson. 
 
 Though the wasting disease has decimated sea stars populations in many coastal regions, new crops of baby sea stars are starting to appear in certain areas. Credit: Maya George 
 
 "Sea stars are known as keystone predators. That means they have a disproportionately large impact on the ecosystem. They’re not that abundant, but if you remove them, it can have this cascading effect," Hewson said. 
 
 Sea stars eat sea urchins and bivalves, such as mussels and clams. But in areas where sea star populations are dwindling, these prey animals have started to take over, altering the natural landscape, Raimondi said. 
 
 For example, the urchin population in some areas has exploded. Sea urchins feed on kelp sporophytes, or seedlings, which later attach to rocks to become kelp forests. Those forests, in turn, are home to juvenile fish as well as a number of organisms that cling to this aquatic plant, Hewson said. Kelp forests are also threatened by an increase in the number of bivalves, which compete with kelp for space atop rocky surfaces. 
 
 However, there is a glimmer of hope amid the demise of the starfish population, which in some areas has decreased by as much as 99 percent, according to Raimondi. 
 
 "Massive numbers of [sea star] babies are showing up, and that's typically a very good sign," Raimondi said. "They usually die because they're small, but if they not only survive but also show up in other places, than recovery could be quick." 
 
 For now, Raimondi is still busy monitoring the health of sea star populations up and down the Pacific coast of North America. He and his colleagues at UC Santa Cruz help keep track of these and other species through Pacific Rocky Intertidal Monitoring, a collaborative research project that collects data on marine populations. 
 
 Raimondi and his team also ask residents of coastal regions to report any evidence of sea star wasting disease in their area. Citizen scientists can see the group's website for more information about how to identify and report the disease. 
 
 The new study was published today (Nov. 17) in the journal Proceedings of the National Academy of Sciences. 
 
 Follow Elizabeth Palermo @techEpalermo. Follow Live Science @livescience, Facebook & Google+. Original article on Live Science.
– Scientists think they finally know what causes sea star wasting syndrome, the disease that's killing off starfish in massive numbers. In a new study, researchers from a number of universities have linked the devastating disease—which causes starfish to rip off their own arms and dissolve into piles of goo—to a waterborne densovirus. "What we're dealing with are animals that are crawling with bacteria and other microorganisms," says the lead author of the study, which looked at 465 sea stars, both healthy and diseased. "Trying to prove beyond a reasonable doubt that any specific virus is responsible for the disease is a really big challenge because you can't isolate it away from those native bacteria. But our evidence is very strong that it's a sea star associated densovirus." Researchers noticed that even sea stars in captivity were coming down with the wasting syndrome, notes LiveScience, seemingly when something got through an aquarium's intake filtration system, which caused them to think an "infectious agent" was behind it. They tested DNA from healthy and sick starfish and detected the presence of the densovirus in the infected samples, then did more testing to confirm their hypothesis—including infecting some healthy starfish with the densovirus; the wasting syndrome set in within 10 days. The next step: Figure out exactly how the virus attacks sea star tissue and identify the trigger for the recent outbreaks, which have depleted populations in some areas by as much as 99%. The virus has likely been "smoldering" in sea stars for some time, Phys.org explains, and the recent epidemic could have been triggered by starfish overpopulation, changes to the environment, or even a virus mutation. (Click for more on the mysterious syndrome.)