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Signs of hope, and a prime suspect, in sea star wasting disease

Washington Sea Grant funded scientists help track down a virus

By Eric Scigliano, Washington Sea Grant

Two years ago scientists noticed that sea stars were dying mysteriously on Washington’s Olympic Peninsula, home to some of the largest and most profuse asteroids (as the stars are properly known) on earth. More sightings followed up and down the Pacific Coast, from San Diego to Southeast Alaska. Sea stars were withering, bleaching, and finally disintegrating into crumbs and slime. Still-vigorous arms would break off from collapsing bodies and crawl away, then collapse themselves. Piers and tideflats the stars had swarmed over a few weeks early were nearly bereft of them.

Researchers dubbed the phenomenon “sea star wasting syndrome.” Last month, in the Proceedings of the National Academy of Sciences, they termed it “the largest known marine wildlife epizootic” ever seen.

Washington Sea Grant (WSG), together with its Oregon and California counterparts, has played a frontline role almost from the start in tracking and investigating the wasting plague. WSG field agent Jeff Adams has trained and deployed about 20 citizen-science volunteers to monitor stars at various Puget Sound sites. They’re part of a statewide monitoring network coordinated by UC-Santa Cruz ecologist Melissa Miner, whom WSG has funded together with her husband Ben Miner, a biologist at Western Washington University.(Oregon Sea Grant also supported Melissa Miner’s work and, together with California Sea Grant and other sponsors, a workshop last summer on West Coast sea star wasting.)

The Miners, along with Oregon and California Sea Grant-supported researcher Peter Raimondi, are members of a multi-institutional team that last month published (in PNAS) the first  evidence of a culprit in the die-offs “Densovirus associated with sea-star wasting disease and mass mortality.” It found strong indications that a virus-sized microorganism is involved.

Genetic analysis identified a type of parvovirus called a densovirus that is related to densoviruses found in Hawaiian sea stars. The researchers named it “sea star-associated densovirus,” or SSaDV. 

They found SSaDV in eight of 11 species sampled, in both wasting stars and, at lower levels, in stars that had not yet shown symptoms, as well as in sea urchins and brittle stars.  the sea stars’ environment, They also found it in water, suspended particles, and sediments, even in aquariums that had experienced wasting disease months earlier. This suggests that the virus can persist in the environment and spread rapidly, even without direct contact – just as wasting disease has.

The researchers looked farther afield, in space and time. They found SSaDV’s DNA in diseased Atlantic sea stars in an aquarium in Connecticut, where mass die-offs had not been observed. And, most intriguingly, they found it in preserved sea stars dating back to 1942.

This, they conclude, “suggests that, like many marine pathogens, SSaDV was already present in the environment before the outbreak.”  Wasting on a much smaller scale also goes back decades, says Melissa Miner.  “In Southern California, sea star wasting has been a persistent phenomenon for years. “The earliest records I’m aware of were in the 1970s. It was associated with big warm-water events in el Niño years.”

Warming waters are one factor that might have helped trigger the current outbreak. Another is overpopulation: fishermen and scuba divers reported a superabundance of sunflower stars (Pycnopodia helianthoides) in Washington’s inland seas in 2012, just before the epizootic took off. Miner cautions against leaping to conclusions: “There are still so many uncertainties. There’s a lot more to the disease than this virus. What’s been established is an association, not causation.”

But she and WSG’s Jeff Adams do note hopeful signs that some stars may be gaining resilience or resistance. A few sites in California and Oregon have recently seen surges of young, apparently healthy sea stars. This led a newspaper in Santa Cruz, where one surge has occurred, to proclaim, “Sea stars making a comeback.”

Miner also counted many more young stars near Bellingham and Cherry Point, Washington near Canada. Further south, says Adams, “we’re seeing a lot fewer big stars, but the ones we’re seeing are mostly healthy.” We’re also seeing a lot of young healthy stars. And there may be a shift in species underway.” Where purple stars previously predominated, mottled stars (Evasterias troschelii) have taken over.  “But that finding is still strictly anecdotal..”

Miner also knows better than to grasp at easy answers. The latest news “is really encouraging, “ she says. “But it’s too soon to tell.” The test will come in May and June, when the waters will warm and sea star wasting disease may reignite again.

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