Sea otters in California are helping to protect kelp forests from an invasion of purple sea urchins. NBC News' Gadi Schwartz visits the Monterey Bay Aquarium to talk to research scientists and to dive ...

This location used to be known for giant kelp so thick it blocked out the sun. However, when Sage swam down, he found hordes of purple sea urchins chewing through what was left of the once dense kelp ...