Purple sea urchins eat kelp spores trying to take root on the sea floor. Urchins grew dominant after people hunted out sea otters and other predators in 1850.
Imagine a grove of trees you can sail down into, 80 feet tall, filled with wildlife. In the Pacific Ocean, that's called a kelp forest. Southern California has lost vast amounts of these underwater forests. In order to restore kelp in a patch of ocean off the Palos Verdes Peninsula, scientists are taking the fight to prospering sea urchins. Reporter: Molly Peterson