Scientists have identified a deadly culprit responsible for a mysterious wasting disease that has killed millions of sea stars along the Pacific coast of North America from Baja California to southern Alaska.

The disease causes sea stars’ limbs to pull away from their bodies and their organs to exude through their skin. Researchers say the disease could trigger an unprecedented ecological upheaval.

A new paper, published in the Proceedings of the National Academy of Sciences, identifies it as the Sea Star Associated Densovirus (SSaDV), a type of parvovirus commonly found in invertebrates, and presents 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 Ian Hewson.

“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.”

The virus has probably been smoldering at a low level for many years, Hawson says. 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 aquaria, sea urchins, and brittle stars also harbored the virus.

‘Experiment of the century’

The discovery lays the groundwork for understanding how the virus kills sea stars and what triggers outbreaks.

The stakes are high, says Drew Harvell, professor of ecology and evolutionary biology and a coauthor of the paper. As voracious predators on the ocean floor, sea stars are “keystone” species that have a large role in maintaining diversity in their ecosystem.

“It’s the experiment of the century for marine ecologists,” he says. “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.”

“The recent outbreak of sea star wasting disease on the US West Coast has been a concern for coastal residents and marine ecologists,” says David Garrison, program director in the National Science Foundation’s Division of Ocean Sciences. “This study, supported as a rapid response award, has made a significant contribution to understanding the disease.”

Geographically diverse samples of diseased stars were provided by citizen scientists, research aquariums, and academic institutions on the West Coast.

The National Science Foundation and the David R. Atkinson Center for a Sustainable Future at Cornell provided rapid response funds.