6/8/14
For more than 40 years, a mysterious disease has been appearing intermittently in populations of sea stars — also called starfish — causing massive die-offs and then disappearing again, sometimes for years at a time. Known as “sea star wasting syndrome,” the disease continues to stump researchers, who have yet to identify a definite cause despite decades of research. Progressing from white lesions that appear on the limbs of affected individuals, the disease causes sea stars to disintegrate and waste away over the course of a week or less, their bodies sometimes physically tearing apart. The mortality rate is estimated to be around 95 percent.
Outbreaks of the illness have appeared sporadically since the 1970s, affecting both coasts of North America as well as the Mediterranean. It was observed in June 2013 in about 20 percent of the Humboldt County sea star population, but appears to have grown significantly worse since then.
“We’re seeing upwards of an 80 percent decline,” said Jana Hennessy, a graduate student in professor Sean Craig’s marine ecology lab at Humboldt State University. She has been working on sea star syndrome since last summer, and said the numbers have changed drastically.
“We haven’t analyzed the data yet, but based on our observations (near Trinidad) there has been a significant decline in the past year, most notably within the last five or six months,” Hennessy said. “A year ago we were counting 160 stars, and a week ago we counted 20, so it’s been pretty devastating. Of the 20 that we saw, about half of them had obvious signs of the syndrome. ... I think we’re pretty close at this point to an extinction event.”
Joe Tyburczy, a marine ecologist with California Sea Grant Extension, said he’d heard anecdotal reports of similar figures from other researchers along the coast.
“In talking with other folks, including a collaborator at Smith River Rancheria who works near Pyramid Point in the new Marine Protected Area … they’re seeing a marked decrease in the abundance of sea stars up there as well. … We’re doing research and getting some baseline data, but our baseline is only capturing numbers after a pretty noticeable decrease,” Tyburczy said.
Oregon was one of the only areas on the West Coast that had remained relatively free of the disease up to this point, but a recent outbreak there has “created an epidemic of historic magnitude” that “threatens to decimate Oregon’s entire population of purple ochre sea stars,” according to a report by Oregon State University science writer David Stauth.
“This is an unprecedented event,” said Bruce Menge, professor of marine biology at OSU. “We’ve never seen anything of this magnitude before. We have no clue what’s causing this epidemic, how severe the damage might be or how long that damage might last. It’s very serious. Some of the sea stars most heavily affected are keystone predators that influence the whole diversity of life in the intertidal zone.”
Their role as “keystone predators” of these intertidal habitats means that as the sea stars die off, whole ecosystems will be disrupted, leading to unpredictable changes for countless other species.
“In a healthy ecosystem, sea stars are beautiful, but also tenacious and important parts of the marine ecosystem. In particular, they attack mussels and keep their populations under control,” Stauth wrote in his article about the Oregon outbreak. “Absent enough sea stars, mussel populations can explode, covering up algae and other small invertebrates. Some affected sea stars also eat sea urchins. This could lead to increased numbers of sea urchins that can overgraze kelp and sea grass beds, reducing habitat for other fish that use such areas for food and refuge.”
Possible causes
Bacteria, viruses, toxins and pollution have all been suggested as possible culprits for the syndrome, but the disease is so widespread that scientists suspect more than one factor could be at work. According to a report from Humboldt State University (http://tinyurl. com/lqtats3), research being done in British Columbia suggests that warmer temperatures may be connected to the rate and severity of infections, though the link is not conclusive.
“Previous outbreaks on the west coast include the 1983 die-off in Southern California that almost completely eliminated Pisaster ochraceus (purple/ochre sea stars) from tidal pools. A smaller scale die-off occurred in 1997 that scientists hypothesized may have been catalyzed by warm waters from El Niño currents; sea stars prefer cooler waters. Warm temperatures have been shown to negatively impact sea star health and can lead to infected wounds,” wrote Jonathan Sleeman, director of the U.S. Geological Survey’s National Wildlife Health Center, in a December report on the syndrome.
“The (recent) outbreak appears more severe than previous outbreaks, killing up to 95 percent of some populations and affecting a much larger geographic area along the west coast. Scientists are compiling mortality reports from the public, monitoring designated sites along the Pacific coast, collecting specimens for diagnostic necropsy, and conducting diagnostic microbiology and genetic sequencing to determine if infectious or toxic agents are involved.”
Marine biologist Kathryn McDonald and a team of six students at HSU’s Telonicher Marine Lab in Trinidad have been studying the problem since September 2013 to see how changes in the environment affect incidence of the disease.
“We’d like to determine whether what we are seeing is truly a contagious epidemic, or something that many sea stars already have — a common infection — that becomes lethal under certain conditions of temperature change or other stress,” McDonald said in the HSU report. “The syndrome is widespread up and down the coast. … There might be more than one disease agent that animals are coping with.”
Though little is known for certain at this point, researchers continue to look for answers.
“There are a lot of people involved in this, and a lot of concern ... so this is being incorporated into a very large, ongoing survey up and down the coast,” said Hennessy.
For more information, including maps of outbreak locations and ongoing monitoring information, visit http://seastarwasting.org.
