North Coast populations decline 90 percent, surge of juveniles continues
11/18/14
Marking a major breakthrough in the mystery of one of the largest wildlife die-offs ever recorded in the world’s oceans, scientists believe they have found the cause of a disease that has killed millions of starfish since last year along California and the Pacific Coast.
The epidemic, which threatens to reshape the coastal food web and change the makeup of tide pools for years to come, appears to be driven by a previously unidentified virus, a team of more than a dozen researchers from Cornell University, UC Santa Cruz, the Monterey Bay Aquarium and other institutions reported Monday.
Scientists found that the same virus that is killing starfish today is also present in museum starfish specimens dating back to 1942, indicating the disease has been present in Pacific waters for 72 years.
Yet although there were smaller outbreaks in years past, nobody knows what triggered the current marine plague, which has killed up to 95 percent of starfish in some areas and spread from Alaska to Mexico.
“Something may have happened recently that caused it to go rogue, because we’ve never seen anything like the current outbreak,” said Peter Raimondi, a professor of biology at UC Santa Cruz and co-author of the study.
The outbreak, known as “wasting syndrome,” has infected at least 20 different species of starfish since it was first detected in Washington’s Olympic Peninsula in June 2013. It spread to Oregon, Humboldt County, Monterey Bay and as far south as Baja California, even killing starfish in major aquariums.
Humboldt State University Marine Laboratory and Marine and Coastal Science Institute Director Brian Tissot said he just returned from a Western Society of Naturalist conference in Tacoma, Washington, where the study was brought up along with a dozen more on sea star wasting disease.
“It’s a pretty significant find to be able to link it to a virus and understand that part of it at this point,” he said. “... Once we do finally know that the disease is a cause of this, the next question becomes to understand what triggered this event and why it continues to propagate from place to place.”
When infected, starfish at first become sluggish, then develop white lesions. Within days, they curl up and parts of their arms break off, sometimes literally crawling away. Not long after, the entire starfish turns into a gooey mess and dies.
In a paper published Monday in the Proceedings of the National Academy of Sciences, the researchers concluded the disease is a type of densovirus. It is similar to viruses that affect insects, sea urchins and other invertebrates, and is distantly related to parvovirus, the cause of feline distemper in cats and canine parvovirus in dogs.
“It’s definitely a huge breakthrough,” said Dr. Mike Murray, director of veterinary services at the Monterey Bay Aquarium. “It provides a lot of other researchers a place to start and say, ‘OK, we found this virus in lots of sea stars. What was the trigger? What started it all off? Are there other problems in other species?’” So far, the researchers found, the virus is present in sea urchins and sand dollars, but isn’t killing them in large numbers. Marine ecologist Joe Tyburczy of the California Sea Grant Extension said the urchins may serve as viral “reservoirs,” spelling bad news for the more susceptible sea stars.
“A species can be totally wiped out in an area,” he said. “If other species that can carry the disease remain, you can keep infecting the all of the most susceptible species.”
The virus spreads in seawater and sand, the scientists discovered. But it does not affect humans. And there is no way to offer a cure to starfish populations.
“It would be nice if we could do that, but it’s too simplistic,” Murray said, comparing it to human epidemics like the Spanish flu of 100 years ago or the Black Death in 14th-century Europe.
“This is one of those natural phenomena that may or may not have a human basis behind it,” he said. “It is going to play itself out, and hopefully it will do that in a way that will allow sea stars to persist. But there are no guarantees.”
Using cutting-edge genetic tools, scientists at Cornell pinpointed the disease.
“There are 10 million viruses in a drop of seawater, so discovering the virus associated with a marine disease can be like looking for a needle in a haystack,” said Cornell microbiologist Ian Hewson, lead author of the study.
Working with 335 starfish collected on the West Coast, the researchers ground up tiny amounts of tissue from infected starfish and injected it into healthy ones in lab tanks, learning how it spread.
Now that they believe they know the culprit, the next step will be to find out why it spread so widely. It could be something natural, like overpopulation of starfish in some areas. Or it could be related to pollution, warming waters or the increasing acidity of the oceans. If triggered by toxics, new laws could make a difference, experts say.
“It is probably part of their population cycle. But if it is driven by something linked to pollution or climate change or things like that, then we would have some responsibility to deal with it,” Tissot said.
While the study found that the disease has occurred in the past, Tissot said the current event is unprecedented in magnitude. On the North Coast, Tissot said there has been about a 90 percent drop in sea star populations. Starfish are key predators in tide pools and near-shore waters.
If their populations don’t recover relatively soon, mussels and other species could explode out of control, affecting other ocean life. Locally, Tissot said the surge of juvenile six-armed sea stars has not let up since August and the juveniles have not shown prolific signs of the disease.
“It’s really an important species and these changes are going to reverberate a long time into the future unless the species starts coming back very quickly,” he said.
