Stewards of the kelp forests: New research reveals how sea otters dramatically influence the climate

With their roly-poly bodies, child-like eyes, long whiskers and tiny padded paws, otters are some of the most charismatic animals in nature. But while being cute doesn’t serve much purpose in the wild, new research suggests these little furballs have been helping mitigate climate change.

A recent study in the journal PLOS Climate, led by researchers from the Monterey Bay Aquarium, details how southern sea otters (Enhydra lutris) off the coast of California have helped kelp forests remain resilient to the impacts of climate change. First the scientists analyzed US government records that inventoried California kelp forests as far back as 1910, compared them with modern information about those same kelp forests today. Then they used a machine learning framework to ascertain and rank the factors that have altered kelp forest density since 1910.

The results were intriguing: While kelp forests suffered dramatic losses along the Northern and Southern coastlines, they had increased in abundance in central California. That is because this is the only region where, despite attempts to hunt them to extinction in pursuit of their fur, southern sea otters have managed to carry on. In fact, in the places where kelp forests were most healthy, otter population densities were at their highest.

The sea otters’ survival proved to be the primary factor in keeping those Central California kelp forests alive and thriving; in fact, they were so successful that those kelp forests helped compensate for losses elsewhere in the state. Kelp canopy declined in Northern California by 63 percent between 1910 and 2016 and by 52 percent in Southern California between 1910 and 2016. But it increased by 56 percent in Central California, thanks to these little creatures in the weasel family. As a result, the overall decline in kelp canopy throughout California between 1910 and 2016 was only six percent.

In terms of fighting climate change, this is quite beneficial as well. Kelp forests contribute immensely to carbon storage and thereby offset the negative impact of humanity’s greenhouse gas emissions. Indeed, kelp forests all over the world capture 4.5 million tons of carbon dioxide from seawater each year. In addition to this benefit, kelp forests aren’t just a metaphor — they really are complex ecosystems home to a variety of lifeforms not unlike a forest on the surface world. During storms, kelp forests shield the coast from destructive erosion, and they also can act as nursery grounds for fisheries. Southern sea otters engage in a number of natural behaviors that help preserve these underwater forests wherever they inhabit — and this is a trend that exists beyond the California coastline.

“Absent from our model, we found similar trends among the Channel Islands with kelp canopy gains along islands where sea otters are observed or recovering (San Miguel and San Nicolas Islands) balancing dramatic losses among all others, where sea otters are absent (Santa Rosa, Santa Cruz, Anacapa, Santa Barbara, Santa Catalina and San Clemente),” the authors explained in their study.

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“Our study showed that kelp forests are more extensive and resilient to climate change where sea otters have reoccupied the California coastline during the last century,” lead author Teri Nicholson, Senior Research Biologist with the Monterey Bay Aquarium Sea Otter Program, said in a statement. “Where sea otters are absent, kelp forests have declined dramatically. In fact, we found sea otter population density as the strongest predictor of change in kelp canopy coverage across this hundred-year span.”

Despite the valiant effort from otters against climate change, they are not immune to it. A 2021 paper in the journal Diversity and Distributions found that three otter species occurring in the Himalayan region — Aonyx cinereus, Lutra lutra and Lutrogale perspicillata — were all vulnerable to climate change, as well as an additional ecological menace: poor land use. Between the two factors, the three otter species are expected to experience a reduction between 6% to 15% and shifting of their geographical range by 2050.

Similarly, a 2018 study from the journal Biological Conservation found that freshwater otters in Africa would as a group be negatively affected by climate change, although some species would suffer more than others; that an Asian freshwater otter known as Lutra sumatrana would actually have an increased and less fragmented range, but one that would often put them in conflict with humans; and that some vulnerable South American species like Pteronura brasiliensis, Lontra provocax and Lutra perspicillata might actually be spared exposure to climate change.

Indeed, a 2023 study in the journal Animals offered a brighter climate change-related prospect for one species of otter, albeit at the expense of another animal. Scientists investigated how climate change and land use policy alterations impacted the interactions of Eurasian otters (Lutra lutra) with Pyrenean desman (Galemys pyrenaicus), a semi-aquatic mammal closely related to moles and shrews.

“We found that the otters will take advantage of these environmental alterations, while desmans will undergo a drastic reduction of their suitable habitats,” the authors write. “In addition, the availability of overlapped range margins between the two species might increase, exposing desmans to a potential increased predation risk by otters.”

All of this research goes to show that animals like otters do a lot more than look cute and sometimes attack swimmers. They play an outsized role in their ecosystems and without them, it would have devastating impacts not just on the coasts of California, but on us. We need these kelp forests to thrive, to absorb our outsized carbon output and to protect our beach front properties from slipping into the ocean thanks to coastal storms and erosion. (Not to mention otters have an inherent right to exist.) Humans are currently driving a mass extinction across the planet — which some experts have described as a “biological holocaust” — with many species at risk of slipping into oblivion. As this otter research demonstrates, the effects of this will not be benign. If we protect otters and other species, we’ll end up protecting ourselves.