An epidemic is destroying sea stars (commonly known as starfish) off the west coast of North America. Until recently, the mysterious disease was destroying the sea star population from Canada to Mexico, but had skipped Oregon. It is now spreading there with frightening speed.

The first sign of sea star wasting syndrome occurs when the stars cross their arms and seem to huddle in on themselves. After this white lesions appear that then turn to holes. Then the entire limb disintegrates to goo, like something out off a horror film. Sea stars often tear off their own legs in an attempt to prevent the infection reaching the rest of their body.

In April researchers at Oregon State University estimated that just 1% of the sea stars in Oregon's waters had the syndrome, and by Mid-May the figure had risen only slightly. Now their estimate is that 30-50% of sea stars in the intertidal zone are affected, and the ochre sea star, a particularly vulnerable species, is likely to become locally extinct. Nine other species have also been observed to be infected to varying degrees of frequency.

“This is an unprecedented event,” said the University's Professor Bruce Menge. “We’ve never seen anything of this magnitude before. We have no clue what’s causing this epidemic, how severe the damage might be or how long that damage might last,”

While sea stars are pretty, we don't think of them as keystone predators like wolves, but Menge says we should. “Some of the sea stars most heavily affected are keystone predators that influence the whole diversity of life in the intertidal zone.” Insufficient numbers of sea stars can allow mussel populations to run out of control. Even more seriously, some sea stars feed on sea urchins, which can devastate kelp and sea grass beds if their numbers grow too high. Since these habitats are important breeding colonies for many fish the effects can be felt far from the intertidal zone.

The syndrome has appeared before, but never with such severity. Researchers do not know if the cause is viral or bacterial, although it seems likely that environmental stresses are making the invertebrates more vulnerable. Recovery from previous events has been unpredictable, with effects varying from short lived to long-lasting without a clear pattern.

Coastal residents who want to help tracking the spread of the sickness are invited to get information on the early symptoms and record observations.

This video from the Oregon Coast Aquarium shows legs torn off by sea stars desperate to get away from the infection.