How did the hunting of sea otters affect kelp forests in the Aleutian Islands?

The hunting of sea otters for the fur trade, which nearly drove the species to extinction by the early 20th century, triggered a dramatic trophic cascade in the marine ecosystems of the Aleutian Islands and the broader North Pacific coast.123

In a healthy ecosystem, sea otters act as apex predators that consume sea urchins, thereby keeping their populations in check. When sea otters were removed due to overhunting, the sea urchin population increased significantly. These urchins feed on kelp, specifically targeting the holdfast—the structure that anchors the kelp to the rocky seafloor.123

By consuming the holdfast, urchins cause the kelp to detach and float away, leading to the widespread destruction of kelp forests. This loss of kelp, which serves as a vital "founder species" that provides habitat and shelter for numerous marine organisms, fundamentally altered the structure of the coastal ecosystem. The subsequent protection and recovery of sea otter populations have been essential in restoring the balance of these environments by controlling urchin numbers and allowing kelp forests to flourish once again.231