'Zombie' Urchins Are Wiping Out Kelp Forests

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California francisco. has a sea urchin problem. They've exploded in numbers off the northern california coast and these purple spiky urchins are wiping out crucial kelp forests so scientists are searching for ways to slow him down. Here's npr's laura summer diving. A kelp forest is a lot like walking through a real forest. The seaweed is thirty to sixty feet tall. It's very surreal. You're kind of coming around. And then you have this large canopy over you. That's kind of filtering light. At least that's how it used to be says. Meredith mcpherson a graduate student at uc santa cruz. She and her colleagues found that ninety. Five percent of kelp forests have disappeared in counties north of san francisco. Cal provides a key habitat for all kinds of marine life. We were expecting something like that. But it doesn't really make it any easier to digest in terms of the actual loss of the coastal ecosystem because of an ecological double whammy. I came marine heat. Wave known as the blob. Water temperatures rose far above normal then came a more direct attack. Purple sea urchins. Their veracious grazers. They devour kelp. Sometimes we see dozens of them. Crawling up the stem of the kelp and kind of taking it down from there. Normally urchins are kept in check by their main predator off northern california a giant starfish sea star scientists call them known as the sunflower see star. But they've been wiped out by sea star wasting disease. Scientists think that both the disease the blob of warm water were made worse by climate change even now with most of the kelp off northern california gone the urgency

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