In the northern Pacific Ocean, sea otters feed on sea urchins and sea stars. Sea urchins feed on kelp, and sea stars feed on mussels. Beginning in the 1700s, sea otters were hunted for their fur and driven nearly to extinction in some areas, resulting in trophic cascades in their communities. When the fur trade ended, sea otter numbers increased and their communities began to recover. When this recovery occurred, which two species would be expected to increase in numbers, and which two species would decrease