Sea Star Wasting Disease (SSWD) is a deadly disease affecting sea stars (a.k.a. starfishes) and other echinoderms - leading to mass mortalities.

At least 20 species are known to be affected.

To date, it has devastated sea star populations along much of the West coast of North America

The first mass 'plague' was noted in 1972 off the East coast of the US.

The cause is unknown, and no infectious agent has yet been discovered. It's presumed to be either viral, bacterial or fungal. And may have be linked to a genetic mutation (i.e. a 'faulty' gene).

More info US Marine Institute