Devastating Starfish Disease May Be Caused by Waterborne Virus

A diseased sea star in California. — 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.

(Image credit: Nate Fletcher)

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]

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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.

"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]

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.

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.