California coastal kelp forests are dying. The culprit? Warm waters and purple sea urchins

A kelp forest off the coast of Northern California is practically gone. An estimated 95% of it has vanished over the last eight years. That’s a problem for marine life that depends on it for food and shelter.

Historically, kelp forests have spanned across approximately 200 miles of the California coast, says marine biologist Patrick Krug. But after a large mass of warm water — known as “the blob” — drifted into the region in 2014, the kelp is no longer recovering. Part of the problem is the purple sea urchin, which have eaten the kelp and have created urchin barrens.

“When the urchins arrived in huge numbers, and the blob was sitting out there making the water temperatures higher than they should have been, there wasn't enough kelp to feed the urchins. When that happens, the urchins mobilize, they leave their hiding places, and they go looking for kelp,” Krug says.