Though millions of sea stars along the West Coast have perished in the past several years from an apparent wasting disease, scientists still don’t know why. The iconic marine creature develops white lesions on its limbs and within days can dissolve or “melt” into a gooey mass. Last year, researchers identified a type of pathogen known as a densovirus as the likely cause, but they still can’t explain the mass die-off three years ago or why a common ocean virus can wreak havoc on so many starfish species from Alaska to Southern California.