Imagine: A sea otter munches urchins. Now imagine that otter in a superhero cape.

It’s true—sea otters along the California coast are heroes right now. (It’s not true that they wear capes. But wouldn’t that be adorable?)

Just how are these cuddly mammals saving the day?

Let’s begin at the beginning. Nutrient-rich algae grows in the waters off California. Sound like dinner? Maybe not to you. But the spiny globs called sea urchins love algae. So do other marine animals. Kelp is a large, brown algae seaweed. Kelp forests are ecosystems composed of kelp. Sea creatures eat from the forests. They live in them too.

But in California, the kelp forest ecosystem has fallen out of balance. A disease almost wiped out the sunflower sea star. That sea star used to eat sea urchins. With no major predator, the urchins multiplied fast—and ate the other sea creatures out of house and home. When urchins go unchecked, they can also create what’s called an urchin barren: sea floor covered in rocks and urchins. Kelp cannot grow in an urchin barren.

In come . . . the otters! In kelp forests, otters are a keystone species. A keystone species is one upon which other species depend. If a keystone species is removed, other creatures in an ecosystem suffer.

Researchers from the Monterey Bay Aquarium in California have been introducing rescued sea otters into a body of water called the Elkhorn Slough (pronounced slue—rhymes with blue). Over time, the otters multiplied. As they did—gobbling up urchins along the way—other species thrived too. Now more than 100 endangered otters swim through this tidal bay every day. They share their home waters with harbor seals, brown pelicans, egrets, and many other animals.

Perhaps these cute critters will come to the rescue along more of the California coast.