Scientists think they know why Pacific sea stars are dying.

Something's been killing sea stars all along the West Coast. And now, scientists have named a primary suspect.

A paper published Monday in the Proceedings of the National Academy of the Sciences names sea star-associated densovirus.

Last year, the Weekly reported on a mysterious illness making sea stars cannibalize one another. They were also losing limbs, their flesh essentially melting away. Scientists called it "wasting disease." Experts have seen several outbreaks since the late 1970s, but this one—hitting sea stars across the U.S. West Coast—may be the first to hit Monterey Bay. But they didn't know what exactly was causing it.

Monday's PNAS paper solves the mystery, naming the contagious densovirus as the likely culprit.

Oregon Public Broadcasting produced an in-depth, multimedia look at the disease. From that report:

When researchers tried to figure out where the virus may have come from, they learned that West Coast starfish have been living with the virus for decades. They detected the densovirus in preserved starfish specimens from as far back as the 1940s.

“It’s probably been sort of smoldering at a low level for a very long time,” Hewson said.

Scientists don’t yet know what sparked the seemingly benign virus to transform into the perpetrator of what’s considered the largest marine disease outbreak ever recorded.