For years, it has been one of the biggest mysteries in marine biology: What is killing the starfish? Since 2013, billions of sea stars, an elegant ocean species commonly known as starfish that are a key part of the environment along the coast of California and other states,

Scientists have solved the mystery of what killed over 5 billion sea stars — also known as starfish — off the Pacific coast of North America

The mass die-off, which began in 2013, saw sea star populations plunge and reshaped vital marine ecosystems in the U.S. and Canada.

Sea star wasting disease has killed billions of starfish and destroyed kelp ecosystems. In a study published Monday, researchers say they found the culprit.