The Keystone Species

Keystone Species are those of any organism that are considered crucial to the structure of the ecosystems in which they belong. The sea otter is an excellent example of a keystone species for the kelp forest ecosystem off the coast of California. Keystone species are important because they help promote biodiversity by controlling species that would otherwise dominate the biological community in which they reside. Also, these species can provide essential resources to other species within the community. Many keystone species are predators like a jaguar, but not all, some are herbivores like the African elephants in the savanna ecosystem.

Without keystone species present, the ecosystems would become dramatically different and many other species could be lost.

The term keystone refers to the center stone of a bridge that is wedge shaped and helps hold the others in place. If this stone is removed the entire bridge should collapse in on itself. The same idea goes for an ecosystem that loses a keystone species. Keystone species are so vital to the communities in which they belong because they are the stone that maintains the structure and function.


An American zoologist Robert Paine was the first to coin the term keystone species back in 1966. While studying the rocky intertidal ecosystem in the Pacific Northwest, Paine observed dramatic changes to the biological community when the Starfish (Piaster ochraceus) was removed.

Of course, one of the most popular examples of a keystone species is the sea otter (Enhydra lutris) within the kelp forest ecosystem. As a member of the weasel family, the sea otter does not posses insulation in the form of thick blubber as many other marine mammals do. Instead the sea otter has an extremely high metabolism and the densest fur of any animal on the planet! The sea otter has such an appetite; it must consume 25 percent of its own body weight daily! Sea otters may appear cute and cuddly to humans, but they are actually voracious predators keeping the populations of invertebrates like sea urchins in check. They provide balance in the kelp forest by controlling the populations of invertebrates that feed upon the kelp.

Unfortunately, Russian fur traders sought after the pelts of the sea otters along the pacific coast of North America throughout the 17 and 1800’s. Eventually traders diminished the otter populations to the brink of extinction. This decimation wasn’t just trouble for the otters, the productive kelp forest ecosystems were greatly affected.

The populations of urchins within the kelp forest ecosystem expanded without sea otters as predator to keep the urchins from overpopulating. Sea urchins graze on the holdfasts of the kelp, and if gone unregulated, they can wipe out whole forests because the kelp can no longer anchor itself and simply floats away. This process can create desolate urchin barrens in areas that were once productive kelp forests. It’s not just the kelp itself that is impacted; there are over 800 species that rely on the kelp for food and habitat. Once the kelp is gone many species disappear with it, thus providing evidence that the sea otter is a vital keystone species.


Since the protection of sea otters, populations have increased in areas like Big Sur and Monterey Bay, California, but they still remain an endangered species. People are not sure if sea otter populations will ever fully recover, but hopefully we can learn from this important keystone species for future decisions facing ecosystems all over the world.

Written By: Chad Brewer