Widely admired for its conspicuous cuteness, the sea otter is proving to be far more than just another appealingly furry face. Research into this keystone species’ role in maintaining carbon-storing macroalgae, commonly known as kelp, indicates that the bewhiskered marine mammals may be important allies in the battle against climate change. One of 13 otter species, and the largest member of the weasel family, sea otters can be found floating about in coastal waters in the United States, Canada, Mexico, Japan, and the Russian Federation. As their name suggests, sea otters spend the majority of their lives in the ocean, preferring to feed, sleep, and raise their pups in close proximity to kelp, which they use as cover from predators and to anchor themselves and their young when resting.
Equivalent to an underwater rainforest, densely layered kelps are an integral component of healthy marine ecosystems, providing food and shelter for myriad species including fish, shellfish, seabirds, harbor seals, and sea lions. In addition to functioning as critical habitat, recent analysis suggests that kelp forests also have immense potential for permanently storing large amounts of carbon dioxide—up to a whopping 634 million tons per year, an amount greater than the annual emissions of Australia.
One of the reasons that kelp is an especially effective sequester of carbon is because it grows quite rapidly, as much as two feet per day, attaching to undersea rocks with root-like structures called holdfasts. Unfortunately, kelp’s natural nemesis, the sea urchin, is particularly fond of feasting on holdfasts, causing the macroalgae to detach from rock surfaces, drift, and die. Left unchecked, the spiny invertebrates can form hungry herds large enough to decimate undersea forests. And that’s where the sea otter comes in—alongside crabs, mussels, and clams, sea urchins happen to be a favorite food of the voracious shellfishionados. By keeping sea urchin populations under control, otters help to ensure kelp’s survival. Researchers at the University of California, Santa Cruz have estimated that the presence of otters in a coastal habitat increased the sequestration capacity of kelp forests by 4.4 to 8.7 megatons—and they support this valuable ecosystem service every day, absolutely free of charge—give or take a sea urchin or two.
When sea otters were hunted for their fur to near extinction in the 18th and 19th centuries, coastal kelp forests and many of the creatures that relied upon them for survival all but vanished. Effectively eliminating the sea otter from its ecological niche had profoundly detrimental cascade effects on other species in its marine community. Although still currently classified as endangered, over the past century, as a result of dedicated conservation efforts, Pacific otter populations have rebounded from a low of several thousand to approximately 148,000 across Canada, Alaska, Washington, and California. And, as the kelp keepers have returned to their historic range, so have the undersea forests and their inhabitants.
As our knowledge of the interdependence of living things continues to evolve, and we learn more about how mutually beneficial relationships between species like sea otters and kelp can help to maintain biodiversity and contribute to ecosystem services such as carbon sequestration, history serves to remind us that in nature, as in life, sometimes you don’t know what you’ve got until it’s gone.
