The Best Way to Combat Climate Change? Send the Otters
The sea otter is a hungry ecosystem engineer of the highest order. To stay warm and healthy, they eat a quarter of their body weight each day, repeatedly diving to the sea floor to gather urchins, crabs, and bivalves like clams. “By eating as much as they can to survive in their environment, they have severe effects on habitats, and they are more positive,” Fujii said. (Another program off the coast of California is trying to bring back a different kind of “killer and urchin”—Dive people.)
Conserving the urchin population preserves kelp, which is important for the ecosystem in two main ways. First, the forest is home to fish, which is a source of food for birds and other marine mammals, such as sea lions. Second, seaweed is part of what scientists call “carbon blue”Ecosystem, means an area of the coast or sea that absorbs carbon. (Other areas include marshy and mangroves.)
But it’s hard to calculate exactly how much carbon is consumed in a healthy kelp forest. A redwood tree, for example, has grown large over hundreds of years, shutting down a lot of carbon over long periods of time. (Unless it is burnt, where carbon returns to the atmosphere.) Things flow more underwater. All kinds of animals, including sea urchins, take in kelp — and take in carbon. In addition, the surrounding sea breaks up fragments of the forest, which fall to the sea floor and decompose, releasing stored carbon. That’s why a kelp forest will always rot and grow back, hiding and releasing carbon all the time.
It is difficult to determine how long the carbon will remain trapped. “The fate of all this kelp is not very well understood,” Wilmers said. “Imagine that all the things that flow fall into the deep sea and never come back again for about 1,000 years. That’s a much more important benefit of following carbon than just sloughing and decay immediately and return to the atmosphere. ”
With uncertainty in mind, Wilmers was able to do some estimates of the potential carbon benefits to healthy otter populations farther north on the Pacific coast, between the Canadian border and the tip of the Aleutian islands. If a kelp forest grows well, and half of the carbon it absorbs is sequestered in the deep sea, this would be equivalent to canceling emissions from 5 million cars. Even if only 1 percent of the carbon remains in the depths, that would be equivalent to emissions from 100,000 vehicles.
In Monterey Bay, otters don’t just protect kelp. They also explored Elkhorn Slough, a large tidal marsh, where they encourage the growth of eelgrass, another coastal plant that takes in carbon — even if otters affect the plant in a more indirectly. Otters feed on crabs, which in turn feed on invertebrates such as sea slugs, which feed on algae that grow on eelgrass. Reducing the number of crabs that fall prey to slugs will really help eelgrass because if the slugs get rid of the algae, it will keep the plants clean, allowing them to absorb more sunlight. Thanks to the return of otters, the amount of eelgrass in Elkhorn Slough is there jumped 600 percent over the past three decades.