Beginning in 2013, a mysterious disease crippled sea star populations up and down the U.S. west coast. Over a matter of months, many sea star species died in record-breaking numbers, though Pisaster ochraceus—a keystone species known as the ochre sea star—was among the hardest hit. Now, researchers at UC Santa Cruz have analyzed just how much the populations of this species have declined, but they have not yet determined what factors might be contributing to the epidemic.