Lauren Sommer

By almost every measure, the drought in the Western U.S. is already one for the record books.

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Coral reef biologists are often asked the same question again and again: "When my kids grow up, will there still be coral reefs?"

"That's a question I ask myself," says Christopher Cornwall, a research fellow at Victoria University of Wellington in New Zealand. "The greatest fear is that all the coral will be gone at a certain point in time."

They're purple, spiky and voracious, and just off the West Coast, there are more of them than you can count.

Purple sea urchins have exploded in recent years off California, covering the ocean floor in what divers describe as a "purple carpet." And they devour kelp: the once-lush forests of seaweed that hugged the coastline are disappearing. Since 2014, 95 percent of the kelp have vanished across a large part of Northern California, most of it bull kelp.

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