Sea Otters: the Cuddly Key to Marine Ecosystem Health

Sea-Otter-LeDent Who doesn’t love sea otters? Anyone who has mindlessly browsed the internet has probably stumbled across pictures or videos of sea otters. Usually they’re holding each other’s paws so they don’t float away or they’re smashing open a shellfish for a midday snack. Recently, sea otters have had a spike in popularity because of the viral videos featuring an orphaned sea otter pup. At Monterey Bay Aquarium, researchers helped the young otter learn some of the skills that it would need to be released back into the wild. Of course, people loved to see the adorable little bundle of fluff hesitantly learning to swim and fetch floating objects. But in the wild, sea otters are not only cute- they are also the key to maintaining the balance of their ecosystems.

Something interesting about sea otters is that they don’t have some of the distinctive traits that other marine mammals have. Unlike the other seafaring mammals, the otters don’t have an insulating layer of blubber; instead relying on their exceptionally thick fur coat (in fact, it is the densest fur of any mammal on Earth). This prevents heat loss when diving into the frigid Pacific Ocean waters, however, the air trapped by the fur also makes diving more difficult.They also have an unusually high metabolism, so they must eat around 20% of their body weight in shellfish every day. Most of the energy from all that food goes toward foraging for more food, although quick grooming is also energetically taxing. The way that the sea otter balances all this high-energy activity is by resting the way humans would in their backyard pools: after they’ve eaten, they spend a long time resting by just floating on the water. So far, the sea otter appears to have a pretty cushy job, with food just a short dive down from your resting spot.

sea otter eatingSea otters typically eat sea urchins, and because of their ravenous appetite, they can quickly and easily decimate the population of urchins in the ecosystem. The sea urchins in turn eat kelp, and if their numbers remain unchecked, they can turn a bustling kelp forest into a barren wasteland dotted with urchins. This means that the sea otter has a very important job: to maintain the kelp forest. Scientists have seen that when otters are reintroduced into a coastal region where they were once common, the community changes dramatically because of the return of the kelp forest. Before the reintroduction of sea otters, a kelp forest could be reduced to an urchin barren devoid of most kinds of life. With the return of the otters, sea urchins are promptly eaten before they have a chance to gnaw off the rooting systems of the kelp. The kelp forest supports many more kinds of sea creatures than the bare ocean floor left by the overgrazing urchins. When there is greater diversity of species, the ecosystem is more stable. It is also protected against drastic changes, such as sudden loss of a species, because there are different species that share similar jobs or functions within the ecosystem. In this way, if one of those species dies out or moves away, another can take its place so that the ecosystem can carry on as it was.

Luckily for us, the sea otters were able to bounce back from the brink of extinction. Historically, sea otters were hunted for their thick, soft furs in their native habitats off the coasts of Alaska and California. Fortunately, the natives of San Miguel found a way to coexist with them without cutting out their fur trade or overhunting the sea otters. The people still hunted the otters for their fur, but only in remote areas away from shellfish beds. These shellfish beds were protected because both sea otters and humans liked to eat red abalones. About six hundred years later, scientists are developing more sophisticated species recovery strategies based on ecosystem function. New methods for evaluating the recovery of a species that had been lost are shifting from demographics (kind of like a head count or census of the recovering population) toward more ecology-based criterion. For sea otters, this new method only requires counting sea urchins, which are far easier to count because they’re pretty sedentary. After that, the number of sea urchins is entered into an algorithm that will provide an estimate of the sea kelp coverage. A kelp-dominated area would be considered to have a fully recovered sea otter population, since they would have eaten most of the sea urchins that prevented the kelp forest from growing. Compared to the old methods of numerous aerial sweeps, this new method is both cheaper and more effective for long-lasting species recovery. In this way, the biologically diverse kelp forest ecosystem is preserved thanks to the sea otters.

Sea-otters-holding-hands_-Photo-credit-2What does this mean for humans? Well, although fisheries are competing with the otters for shellfish, the reestablished kelp forest will attract more types of fish for us to eat. Sea otters can also provide a boost in tourism in the same way that whale watches do. Tourists would love to see an adorable sea otter in the wild. They can take pictures of the otters holding hands or watch them cleverly use rocks as tools to break open a clam the same way they would at a restaurant (although with a more sophisticated tool than a rock). I’m sure the Monterey Bay Aquarium can attest to the popularity of otters with tourists, as many are probably eager to see the baby sea otter from the viral videos.