ARI SHAPIRO, HOST:
In the Pacific Ocean's kelp forests, the seaweed can be taller than trees. This vital ecosystem has been disappearing largely because of the loss of sea stars. They've been ravaged by a mysterious disease. Now, as NPR's Lauren Sommer reports, researchers have figured out what it is.
LAUREN SOMMER, BYLINE: It's known as sea star wasting syndrome. And it's not a nice way to go.
ALYSSA GEHMAN, BYLINE: It's pretty gruesome.
SOMMER: Alyssa Gehman is an ecologist at the Hakai Institute, a scientific research center in British Columbia. She studies diseases and sea stars. Scientists don't call them starfish anymore, by the way. Gehman says, first, the sea stars get lesions.
GEHMAN: And then their arms actually detach and sort of walk away from their bodies. And then eventually, they just dissolve completely into sort of a pile of goo.
SOMMER: Researchers first noticed it off the West Coast more than 10 years ago. Sea stars started dying off, including the giant three-foot sea star, the sunflower sea star.
GEHMAN: They can have up to 24 arms. They actually start with five and then just keep getting more and more arms as they grow. Most of the animals on the bottom of the ocean floor run away from them.
SOMMER: Purple sea urchins definitely run because sunflower sea stars eat a lot of them. That actually helps the whole kelp forest because urchins are voracious eaters of kelp. So when the sea star started dying off, the urchins boomed, and the kelp started disappearing. In parts of northern California, 95% of the kelp was gone.
GEHMAN: It's a really good example of how everything is linked.
SOMMER: For years, researchers didn't know what was causing the sea star disease. Just like us, they have a lot of bacteria and viruses in them all the time. Gehman and her colleagues spent four years studying infected animals in tanks and finally narrowed it down.
GEHMAN: It was incredibly clear. Essentially, the exposed animals had a long list of one pathogen, and that was Vibrio pectenicida.
SOMMER: It's from a group of bacteria that can cause problems in humans, too, like cholera and food poisoning. Gehman says it's not clear exactly where this strain of the bacteria came from, but identifying it could lead to ways of dealing with it.
KEVIN LAFFERTY: I think it opens so many doors. If you don't know what's causing the disease, you're kind of stuck.
SOMMER: Kevin Lafferty is a senior scientist with the U.S. Geological Survey who was not involved with the research. He says, now, researchers can test for this bacteria to see how it's spreading in the ocean. And it will help researchers who are breeding sunflower sea stars to release into the wild.
LAFFERTY: You want to have a bunch of sea stars that you breed, and you want to expose them to the pathogen, right? And then you can see who remains, who's left standing, so to speak.
SOMMER: Those sea stars would be more resistant to the bacteria. That means there's a chance they could return to the kelp forests that need them. Lauren Sommer, NPR News.
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