Virus fingered as top suspect in West Coast sea star wasting disease
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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.
Limbs pull away from the sea stars' bodies and organs exude through their skin.
The first symptom is white lesions that appear on the surface of the starfish and spread rapidly, followed by decay of tissue around the lesions. Eventually the sea stars' bodies begin to break down; the starfish may die within a few days.
It's a disease researchers say could trigger an unprecedented ecological upheaval under the waves.
Now scientists have identified the deadly culprit as Sea Star Associated Densovirus (SSaDV).
Sea star wasting disease widespread along West Coast
At the beginning of September 2013, a die-off of starfish was reported off the coast of British Columbia. The seabed was strewn with disintegrating sunflower stars and morning sun stars.
By November 2013, ochre stars, usually common on mussel beds in places like California's Natural Bridges State Marine Reserve, had vanished from such locales.
"The recent outbreak of sea star wasting disease on the West Coast has been a concern for coastal residents and marine ecologists alike," says David Garrison, a program director in the National Science Foundation (NSF)'s Division of Ocean Sciences, which funded the research.
"This study, supported as a rapid response award, has made a significant contribution to understanding the disease."
In a paper in this week's issue of the journal Proceedings of the National Academy of Sciences, microbiologist Ian Hewson of Cornell University and colleagues present the results of a genomic analysis of the 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 Hewson.
"Not only is this the discovery of a virus involved in a mass mortality of marine invertebrates, it's also the first virus described in a sea star."
Virus smoldering at low level for years
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.
Seawater, plankton, sediments and water filters from public aquariums, as well as sea urchins and brittle stars, also harbor 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 Cornell ecologist and evolutionary biologist who is a co-author of the paper.
As voracious predators on the seafloor, starfish are "keystone" species that play large roles in maintaining diversity in the ecosystem.
Marine infectious disease "experiment of the century"
Geographically diverse samples of diseased sea stars were provided by citizen scientists, research aquariums and academic institutions along the West Coast.
Their contributions were facilitated by Harvell's NSF grant for a Research Coordination Network for the Ecology of Marine Infectious Disease.
Sea star wasting disease "is the 'experiment of the century' for marine ecologists," says Harvell.
"It's happening to sea stars--important predators of the tidal and sub-tidal zones--on a very large scale. Their disappearance is an experiment in ecological upheaval the likes of which we've never seen."
In addition to NSF, Cornell University's David R. Atkinson Center for a Sustainable Future provided rapid response funds to Hewson and scientist Ben Miner of Western Washington University.