The sweetest way to fight climate change? Send the otters

The sea otter is a predatory ecosystem engineer of the highest class. To stay warm and healthy, they eat a quarter of their body weight a day, repeatedly diving to the seabed to collect hedgehogs, crabs and bivalves like mussels. “Because they have to eat as much as they do to survive in the environment, they have a really drastic impact on these habitats and they are extremely positive,” Fuji said. (Another program up the coast of California tried to bring back a different kind of “hedgehog killer” – divers.)

Maintaining the hedgehog population preserves algae, which are vital to the ecosystem in two main ways. First, the forest is a habitat for fish, which are a source of food for birds and other marine mammals, such as sea lions. Second, algae are part of what scientists call the “blue carbon” ecosystem, which means a coastal or marine area that captures carbon. (Other areas include wetlands and mangrove forests.)

But it is difficult to determine exactly how much carbon a healthy forest of algae absorbs. Redwood, for example, has been massive for hundreds of years, blocking a lot of carbon for long periods of time. (Unless it ignites, in this case the carbon is returned to the atmosphere.) Underwater, things change more. All species of creatures, including sea urchins, bite algae and release carbon. In addition, the raging sea tears pieces of the forest that fall to the seabed and decompose, releasing the accumulated carbon. So the algae forest is constantly falling apart and growing again, capturing and releasing carbon all the time.

It is difficult to say how long carbon remains trapped. “The fate of all these algae is not well understood,” says Wilmers. “Imagine that everything that is released just sinks into the deep ocean and will not return again in about 1,000 years. This is a much more significant benefit of capturing carbon than simply releasing it and decomposing it immediately and returning it to the atmosphere. ”

Given this uncertainty, Wilmers made some estimates of the potential benefits of carbon from healthy otter populations further north along the Pacific coast, between the Canadian border and the top of the Aleutian Islands. If the algae forest grows well and half of the carbon it absorbs is isolated in the deep sea, this would be equivalent to eliminating the emissions of 5 million cars. Even if only 1% of the carbon remained isolated at depths, this would be equivalent to the emissions of 100,000 cars.

In Monterey Bay, otters don’t just protect algae. They also climb Elkhorn Slough, a large tidal swamp where they promote the growth of eelgrass, another coastal plant that captures carbon, although otters affect the plant in a more indirect way. Otters eat crabs, which in turn eat invertebrates like sea snails, which eat algae that grow on the grass of the snake. Reducing the number of crabs that prey on snails actually helps snails, because when snails remove algae, it keeps plants clean, allowing them to absorb more sunlight. Thanks to the return of otters, the amount of eel grass in Elkhorn Slough has jumped 600 percent in the last three decades.