Sea otters are mammals that belong to the weasel family, have the densest fur of all animals and are a keystone species. As a keystone species, the sea otter is critical for the health and well-being of a great number of other species. They are the heaviest weasels and the second smallest marine mammals.
The sea otter feeds mostly on marine species, such as urchins, mussels, clams, crabs and snails. It has an extremely high metabolism, which means that it has to eat a lot, nearly a quarter of its weight each day in food. The sea otter has no layer of blubber although it spends the majority of its life in water. Instead, it has extraordinarily dense fur, which contains between a quarter of a million and a million hairs per square inch.
The sea otter lives off the coast of the Pacific Ocean, though the species once ranged along Japan, Siberia, Alaska, British Columbia and the West Coast. The fur trade has drastically reduced its numbers. As a keystone species, the sea otters keep the populations of marine life down, which keeps that marine life from decimating kelp forests. Kelp forests, in turn, help to reduce carbon dioxide levels.