Sea otters defend CO2 absorbing kelp forests

social sea otters
Sea Otters socializing, Morro Bay, CA. / Attribution Michael L. Baird (Creative Commons Attribution 2.0 Generic)

The fur trade halted abruptly with the International Fur Seal Treaty of 1911, which finally forbade commercial harvesting. Hunters and trappers had run rampant during the last two centuries. The species of sea life they harvested for pelts during the 18th and 19th century were decimated: Northern fur seal populations were incredibly rare, and Sea otters were believed to be completely extinct. Then, in 1938 a small group of Sea otters was discovered living off the coast of Big Sur, California. The species has been struggling to recover ever since.

sea otter pelts
Sea Otter skins, Unalaska, 1892. / Courtesy Stefan Claesson, NOAA’s Historic Fisheries Collection

“When they discovered that population off California in the thirties it was like they discovered dinosaurs,” noted conservation biologist Shawn Larson of the Seattle Aquarium. Larson studies Sea Otter genetics. By extracting DNA samples from Sea Otter teeth found in archaeological digs at ancient indigenous settlement sites, she mapped proof that Sea otters which lived 400 to 600 years ago had twice the genetic diversity that they have today. Before the fur trade there might have been 150,000 otters scattered along Pacific Ocean coasts from Japan north to Alaska and back south through California. After the fur trade, fewer than 1,000 Sea otters remained.

Humans have helped otters recover

Today Sea otters can be found in nearly two-thirds of their historic range, with populations in Alaska, Washington, California, Canada, Russia, and Japan. You can see them socializing in otter groups called rafts, wrapping themselves in kelp fronds or clasping paws with neighbors to avoid drifting apart while they sleep.

Their recovery, one hard-won through the cooperation of dedicated policy makers, conservationists and environmentalists, is inspiring. Strong efforts to stop hunting and poaching, reintroduction programs that brought otters back to historic ranges, impressive feats by aquariums that rescued precious orphaned cubs, and efforts that cleaned and rehabilitated oil-covered otters have all played their part.

Humans still present major risks

While Sea otter populations have rebounded, the species is still at risk. Oil spills threaten Sea otters. The Exxon Valdez oil spill killed almost 4,000 individuals. The otters rely on their super-dense fur for insulation and warmth. Oiled fur doesn’t insulate. Licking and grooming oiled fur poisons the otter, and oil-affected otters die of digestive problems, lung damage, and hypothermia.

The human fishing industry is a threat to Sea otters. Fishing nets and other fishing gear, especially that discarded in the ocean, injure Sea otters (and all sea life). During the 1970s and 80s, gill and trammel nets drowned many otters. Competition with human fishers who overfish food sources can put serious stresses on recovering otter populations. Shellfish fisheries that might lose stock to hungry Sea otters often oppose conservation efforts that aim to reintroduce Sea otters to their nearby historic range.

After World War II, there was a whaling boom that killed off baleen whales over much of the north Pacific. By 1960 or 1970 they were so few in number that Killer whales could no longer rely on baleen whales as a food source. Killer whales in the north Pacific switched to eating Harbor seals, Northern fur seals, Steller sea lions, and finally Sea otters, thinning each species’ populations out one-by-one. Populations of otters along the Alaskan and Canadian coast, which had recovered to a few hundred thousand, were driven back down to just a few thousand.

Sea otters are still classified as endangered. They are vulnerable to anthropogenic (human-caused) threats. And, like species the world over, they are threatened by the many changes that a warming climate inflicts on plants and animals alike.

Otters make kelp forests healthy

Professors Chris Wilmers and James Estes, University of California Santa Cruz, have combined 40 years of data on otters and kelp bloom from Alaska’s Aleutian Islands and along the Pacific coast to Vancouver Island. Their research illuminated how Sea otters act as climate defenders when they inhabit kelp forests. Their findings were published in Frontiers in Ecology and the Environment.

happy grooming sea otter
Sea Otter grooming, Moss Landing, California. / Attribution Sstasi (Creative Commons Attribution-Share Alike 3.0 Unported)

Otters are keystone predators in northern Pacific marine ecosystems. They hunt and eat Sea urchins, which are spiky slow moving plant-eating animals. Sea urchins pose a humongous threat to kelp forests because they multiply quickly and eat at the holdfasts (roots) of kelp forests, feeding on the kelp frond where it attaches to the ocean floor. The damage can sever kelp from its roots and cut the kelp off from ocean sediment nutrients.

When otters are present, they control Sea urchin populations. Sea urchins hide from otters in rock crevices. Instead of taking down living kelp plants through overgrazing, they feed on naturally-fallen kelp detrius. Sea otters’ presence is crucial in keeping the ecosystem balanced and the kelp forests healthy and thriving. And, even if you live far from the Pacific Ocean, that matters to you because kelp forests are one of the ocean’s great carbon sinks; they help mitigate the effects of climate change.

Kelp forests sequester carbon

Plants communities can serve as carbon sinks, or places where carbon is removed from the atmosphere for a long time. Plant life relies on photosynthesis, and carbon dioxide is required for the process. Carbon dioxide is drawn from the atmosphere (or from the ocean, which is itself a great carbon sink) and oxygen is released, leaving carbon trapped in the plant itself. A growing plant continues to act as a carbon sink. When kelp leaves sink to the ocean floor, they can remain there without decomposing for decades or even centuries, which keeps carbon sequestered on the ocean floor instead of free in the atmosphere.

We’re already working to save rainforests that sequester huge amounts of carbon dioxide; the United Nation program Reducing Emissions from Deforestation and Forest Degradation finds economic mechanisms to incentivize developing countries to protect their rainforests. Why shouldn’t kelp forests also be protected?

kelp strand fish aquarium
Kelp forest exhibit, Monterey Bay Aquarium, California. / Attribution Stef Maruch (Creative Commons Attribution-Share Alike 2.0 Generic)

Kelp forests don’t only sequester carbon. They provide many ecological benefits. Kelp serves as an ecosystem foundation: feeding and sheltering diverse ocean species. They’re a vital habitat for schools of fish. Kelp forests also reduce coastal erosion and serve as a buffer against strong storm-born waves. Since climate change will likely heighten the severity of weather events like storms, the protection kelp forests provide coastal communities will be a major benefit.

By the numbers

*Kelp forests accompanied by Sea otter defenders sequester as much as 12 times the amount of CO2 from the atmosphere than kelp forests with unchecked Sea urchin populations.

*The presence of otters increases kelp forest carbon storage by 4.4 to 8.7 megatons anually. It would take 3 to 6 million passenger cars to equal that amount of carbon dioxide pumped into the atmosphere.

*Calculating with the current price of carbon on the European carbon market, the carbon sequestered by kelp forests protected by Sea otters would be worth $205-$400 million.

The United States doesn’t participate in the European carbon market, but the U.S. does aim to meet a modest commitment of a 17% reduction from 2005 carbon pollution levels by 2020, with the ultimate goal of reducing carbon pollution by 83% below 2005 levels by 2050.

Win-Win scenarios

Managing Sea otter populations creates healthier ecosystems. Healthier kelp forests sequester more carbon from the atmosphere. Of course, it’s only one puzzle piece in a larger effort to reduce humanity’s carbon footprint. But it’s one that can benefit carbon sequestration and wildlife conservation alike. Opponents of costly conservation efforts should be able to see that the economic costs of conservation efforts for species like the Sea otter can be offset or even overshadowed by the economic benefits. Professor Chris Wilmer realizes that large predators can impact the global carbon cycle. He notes that “Animals the world over, working in different ways to influence the carbon cycle,” could potentiall have a large impact on how we approach mitigating climate change damage. “If ecologists can get a better handle on what these impacts are, there might be opportunities for win-win conservation scenarios, whereby animal species are protected or enhanced, and carbon gets sequestered.”


Laura Nielsen

Frontier Scientists: presenting scientific discovery in the Arctic and beyond