These Fluffy Sea Otters are a Keystone Species


The last week of September each year has been designated Sea Otter Awareness Week in order to promote the essential role that these excessively cute marine mammals play in nearshore ecosystems.  As consumers of sea urchins and clams, sea otters help maintain the health of kelp forests.  Healthy kelp forests means an abundance of food for a wide range of fish and sea life which in turn supports economic and commercial activities.  Sea Otter Awareness Week is celebrated each year by museums, aquariums, schools, and other institutions around the world.

Sea otters are native to marine environments in the North Pacific Ocean.  Heavy hunting for their fur between 1741 and 1911 led to a precipitous drop in numbers of this species.  Conservation efforts have helped the number of sea otters rebound from a low of around one to two thousand to a little over 100,000 today.

Sea otters are what are known as a keystone species. Keystone species are plants or animals whose presence in an ecosystem plays a crucial role in its health.  The term was first coined by Robert T. Paine, a professor of zoology at the University of Washington in 1969 who used the term to describe the importance of Pisaster ochraceus, a species of starfish, and Mytilus californianus, a species of mussel.  By keeping benthic (sea floor) herbivores such as sea urchin populations in check, sea otters preventing an over consumption and die off of sea kelp.  Kelp is critically important as it provides habitat and food for a large number of fish, invertebrates, birds, and marine mammals.

Sea otters spend the majority of their lives in the water, eating, playing, and even sleeping in the ocean.  Living in a fluid environment, sea otters have come up with various ways to keep from floating away while sleeping.  Sea otters may wrap themselves in sea weed to anchor themselves.  Another strategy is to hold hands to keep family groups together.  A group of sea otters is known as a “raft”. Sea otters in a raft will hold paws while sleep to keep the group from floating apart.

Milo and Tanu, two sea otters housed at the Vancouver Aquarium demonstrate this adorable trait:


Paine, R.T. (1969). “A Note on Trophic Complexity and Community Stability”. The American Naturalist 103(929): 91–93. doi:10.1086/282586JSTOR 2459472.


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