Mon June 30, 2014
Scientists Close In On What’s Killing Sea Stars
On the west coast sea stars, or starfish, are dying by the millions. Scientists have called the disease Sea Star Wasting Syndrome, and it’s decimated populations from Mexico to Alaska. But scientists aren’t exactly sure what’s causing the die-off. This spring, the epidemic has spread into Oregon, and now, Hood Canal and the San Juan Islands in Washington.
The village of Eastsound on Orcas Island draws thousands of tourists in the summer months. They come to see whales, bald eagles… and for avid beach combers -- sea stars.
In fact, the little beach in Eastsound is a sea star hotspot. Thousands of them cluster in the nooks and crannies of this rocky patch of island coast.
But that may not be the case for much longer.
Drew Harvell: “Well I’ll tell you, Ashley, it’s a lot worse than it was last week, which is what we expected but it still doesn’t help to see the future when you see it. Look at all these…”
Drew Harvell has been studying marine disease for decades. She’s a marine epidemiologist with Cornell University and the University of Washington.
The Sea Star Wasting Syndrome has just arrived in the San Juan Islands – after decimating populations up and down the west coast. Scientists think the cooler waters and swift currents surrounding these islands may have been protecting the population.
But now the sun’s out, the water’s warming, and the sea stars are getting sick.
Harvell points at a handful of orange and purple stars nestled into the rocks nearby. One’s arm is hanging on by a single gnarled string of flesh.
Drew Harvell: "It looks dried out, wasted, thin, deflated. Sea stars are not supposed to look like that."
Last week when Harvell’s team visited this site they found 1 out of every 10 stars was sick.
Now almost half of the sea stars here are showing signs of the wasting syndrome.
Drew Harvell: “There’s a lesion on this one. Let’s get a picture of that. That’s the next stage is the appearance of lesions and then the bad part is the arms start to tear off.”
Harvell says this is the largest documented marine epidemic in human history.
Scientists have confirmed that there is an infectious agent to blame – but they’re not sure if it’s a bacteria or a virus. It appears to be transmitted through the water, or through physical contact.
Drew Harvell: “Most of the stars in our waters probably already have been exposed…because if we bring them into the lab, and expose them to temperature stress, they get sick.”
Warm water stresses out sea stars – sort of like when you’re fighting a cold and you get overtired - and then the sickness takes hold. So the hypothesis is that warmer waters may not cause the disease, but they can exacerbate it.
That hypothesis seems to hold true further down the coast. Carol Blanchette is a research biologist at UC Santa Barbara whose been following the disease outbreak there.
Carol Blanchette: “Sea stars across Southern California have been pretty much wiped out at most sites and the period of time in which the disease has progressed rapidly has been a period in which waters have been warmer than usual winter conditions.”
But there’s another new hypothesis that Blanchette wants to explore. She thinks there could be a connection to what sea stars are eating.
UC Santa Barbara has an aquarium right on the ocean. The tanks are filled with seawater that’s pumped in. The aquarium’s sea stars got sick at the same time as the nearby wild population did.
But then scientists noticed something interesting. In one tank, sea stars were being fed mussels that were harvested from the shore near the aquarium.
In another tank the sea stars were fed frozen squid.
The stars that ate the wild mussels got sick. The stars that ate the squid, didn’t.
Carol Blanchette: “I don’t want to make too much of this because it’s a very small sample size but it is interesting that there may be a link to acquiring the disease through the food that they’re eating.”
As filter feeders, mussels could be concentrating the pathogen in their flesh. And sea stars eat a LOT of mussels.
So what happens if all the sea stars die off? They’re an apex predator - a keystone species.
Carol Blanchette: “Losing a predator like that to the system is bound to have some pretty serious ecological consequences and we really don’t know exactly what the system is going to look like in the absence of having those predators around but we’re quite certain that it’s going to have an impact.”
Scientists at Cornell hope to identify the pathogen behind sea star wasting syndrome in the coming weeks. Their findings will be submitted to the journal Science.
Sea stars have survived mass wasting syndromes in the past, but no one has ever seen a die off as big as the one taking place on the West Coast now.
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