Sea otters — Enhydra lutris — are keystone species in the kelp forest ecosystems of the North Pacific coast.

Their feeding on sea urchins maintains the kelp forest by controlling urchin populations that would otherwise overgraze the kelp.

The presence of sea otters therefore contributes to the productivity of the entire kelp forest ecosystem, which provides habitat for a wide range of fish species that are important prey for both marine mammals and human beings.

Sea otters were hunted to near-extinction in the Pacific fur trade of the eighteenth and nineteenth centuries, their fur being among the most valuable animal products in global trade.

The near-elimination of sea otters had cascading ecological effects on the kelp forest ecosystems of the coast.