Mysterious 'Seastar Wasting Disease' Die-Off Along US West Coast Baffles Scientists

By Josh Lieberman on November 5, 2013 6:35 PM EST

starfish
A mysterious disease is turning scores of starfish into slime, from Southern California up to Alaska. (Photo: Wikimedia Commons)

It begins with white lesions forming on the arm. Over the course of a few days, the lesions spread inward. In less than a week, the animal has disintegrated and is dead.

A mysterious disease is turning scores of starfish into a slime along the west coast of the United States, and scientists aren't quite sure what is causing it. First detected in June, "seastar wasting disease" has decimated starfish populations from Southern California to Alaska, killing off starfish populations entirely in some areas. (By the way, "seafish" and "starfish" mean the same thing.)  

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"It's pretty spooky because we don't have any obvious culprit for the root cause even though we know it's likely caused by a pathogen," said Pete Raimondi, chair of the Department of Ecology and Evolutionary Biology at the University of California at Santa Cruz's Long Marine Lab. Raimondi noted that seastar wasting disease has occurred periodically for decades, but it's usually found in small numbers. 

"The proximal cause of the disease, when pathological studies have been done, is typically a bacterium (vibrio), although a recent wasting event on the east coast of the United States has been attributed to a virus," reads UC Santa Cruz's Ecology and Evolutionary Biology website. "The ultimate cause is not clear although such events are often associated with warmer than typical water temperatures as was the case for the major die off in southern California in 1983-1984 and again (on a lesser scale) in 1997-98." The website calls the 2013 starfish die-off "particularly troubling" because of how massive it is.

Raimondi doesn't know how many of the millions of starfish along the coast have contracted seastar wasting disease. But in one surveyed area in Santa Cruz, 90 to 95 percent of the starfish population was wiped out, so things could be pretty bleak.

Of the 10 types of starfish currently affected by seastar wasting disease, the species Pisaster ochraceus has been hit in the greatest numbers. Pisaster ochraceus is a mussel-eating starfish, and if a lot of them die off, then mussel populations could flourish in the Pacific. When a large population of mussels is able to explode, the creatures can cover surfaces usually occupied by barnacles and algae, driving them out completely.  

"Seastars are not eaten by anything, and their predation has a dramatic effect on the rest of the community," Raimondi told the Los Angeles Times. "What they do is take out the mussels, and without seastars, the mussels would dominate the space."

UC Santa Cruz has created a map of locations where people have reported starfish missing limbs (something which could be evidence of seastar wasting disease). This week, scientists in California, Washington and Oregon will begin a survey to determine the extent of the 2013 starfish die-off. 

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