Since 2013, millions of starfish have perished along the West Coast, victims of a mysterious illness called sea-star wasting disease. Now scientists think they might have a clue into what’s causing the massive die-off. A recent study in Proceedings of the National Academy of Sciences links the wasting to a virus that’s been floating around our oceans for at least 70 years. But is the virus the only culprit?

The time-lapse video below shows a starfish infected with the disease.