Mass sea star deaths off West Coast stump scientists


Starfish have been mysteriously dying by the millions in recent months along the U.S. West Coast, worrying biologists who say the creatures are key to the marine ecosystem.

Scientists first started noticing the mass deaths in June 2013. Different types of starfish, also known as sea stars, were affected, from wild ones along the coast to those in captivity, according to Jonathan Sleeman, director of the U.S. Geological Survey’s National Wildlife Health Center. “The two species affected most are Pisaster ochraceus (purple sea star or ocher starfish) and Pycnopodia helianthoides (sunflower sea star),” he wrote in December.

The sunflower sea star is considered among the largest starfish and can span more than 1 meter in diameter.

The most commonly observed symptoms are white lesions on the arms of the starfish. The lesions spread rapidly, resulting in the loss of the arm. Within days, the infection consumes the creature’s entire body, and it dies.

Entire populations have been wiped out in Puget Sound off the coast of Washington state, in the Salish Sea off Canada’s British Columbia, and along the coast of California. The mortality rate is estimated at 95 percent.

Scientists who have spent decades studying the local ecosystem have yet to identify the cause.

“What we currently think is likely happening is that there is a pathogen, like a parasite or a virus or a bacteria, that is infecting the sea stars and that compromises in some way their immune system,” Pete Raimondi at the University of California, Santa Cruz, said. Then the creatures become more susceptible to bacteria, “causing a secondary infection that causes most of the damages that you see.”

Starfish are important because “they play a key role in this ecosystem on the West Coast,” Raimondi said. Starfish eat mussels, barnacles, snails, mollusks and other smaller sea life, so their health is considered a measure of marine life on the whole in a given area. When starfish decline in number, the mussel population can dramatically increase, which could significantly alter the rocky intertidal zone.