Sea otters are a keystone species. Without its keystone species, an entire ecosystem can fall apart. Wherever sea otters have disappeared, kelp forests have suffered. Urchins eat kelp, and sea otters eat sea urchins. In places where sea otters have disappeared, sea urchins will eat the kelp forest until it\'s gone. They leave behind desolate areas called urchin barrens. Researchers found that when sea otters arrive in an area from which they have been absent, they begin snacking on urchins. Soon the kelp forest begins to grow back. Algae species that had been missing make an appearance, along with fish that like to hide out in the canopy.