Starfish struck by disease

02/06/2014

The night sky may still be full of them, but our tide pools are suddenly dark and empty. A disease known as sea-star wasting syndrome has caused significant harm to starfish along the West Coast, decimating the population in Marin, local scientists and beachcombers said.

George Clyde, a Marshall resident, meandered through the tide pools last week from McClures to Kehoe Beaches on a hike he has taken multiple times over the past decade. One of the highlights of the trip had always been the abundance of sea stars, a numberless rainbow that colored the pools and caves in the brilliant purple, orange and red of the prevalent ochre sea star. There were usually hundreds in sight, covering the rocks with their long, pointed legs.

This year, he saw one. Other hikers on the walk counted maybe a handful.

“I’d not really given a thought to it, but when I got to the end of the hike, I realized we hadn’t seen any at all,” Mr. Clyde said. “They were just absent.”

A group of citizen scientists, mostly high school students, has monitored regularly at Duxbury Reef in Bolinas. Last week, there were no sea stars in sight, said Amy Dean, the education manager for Long-term Monitoring Program and Experiential Training for Students, or LiMPET. The population had been slowly declining over the last 10 years, but the group first noticed a huge change in October.

Research teams from University of California, Santa Cruz have found sea stars with lesions and other signs of the disease along Point Reyes in recent months, said Ben Becker, a marine ecologist with Point Reyes National Seashore. Counts a bit further south, near Slide Ranch, turned up no abnormal numbers or evidence of disease, he added.

Lesions first appear on the sea star and the body can appear deflated with its arms unnaturally twisted. The tissue decays to the point where the body fragments, causing death. The disease was first reported by a team from Olympic National Park in Washington in June and has since been documented from Alaska to Southern California.

Scientists are unsure what has prompted the die-off. Speculation has ranged from low oxygen levels in the water, hazardous waste runoff and even radiation from Fukushima, but these have been mostly been dismissed. It could be related to climate change, ocean acidification or a foreign disease transported on a ship.

Sea-star wasting syndrome has surfaced twice before during warm water years in the early 1980s and to a lesser extent in the late ‘90s, although the recent appearance has been much wider in geographic scope and magnitude of the mortality. As the sea change continues, researchers are trying to figure out exactly what the pathogen could be—a bacteria had been previously suspected, but cases on the East Coast appear to be caused by a virus—and how it spreading.

The decline in sea stars could shift existing relationships in the tide pools, altering the look of the seascape. Starfish are one of the most voracious organisms in tide pools, where they feed on mussels, clams, sea cucumbers and even other starfish, so their absence could mean unchecked mussel beds crowding out other species, Dr. Becker said.

“The ochre sea star is a keystone species, meaning it has a large impact on the ecosystem relative to its number,” he explained. “It shifts the way the community looks if you take the top predator out, like taking the wolves out of Yellowstone or lions off the Serengeti. It cascades down through the system.”