The Pacific sea otter was hunted to near extinction in the early 1900s. The loss of this predator resulted in several changes to the kelp forest ecosystem. Populations of sea urchins, which are one of the sea otters' favorite prey, grew to historically high numbers. Sea urchins graze on kelp, and the extremely large populations of sea urchins significantly reduced kelp biomass. Researchers have hypothesized that overgrazing of kelp by urchins may have hastened the extinction of the Stellar's sea cow, which also depended on kelp as a food source. Identify the ecosystem relationships that were disrupted in the kelp forests by the loss of sea otters.