Research reveals sea otter climate impacts in the form of powerful carbon storage through kelp forest protection.
Sea otter climate impact extends far beyond their adorable appearance as these marine mammals fight climate change every day by protecting underwater forests that store massive amounts of carbon dioxide. Scientists now recognize sea otters as keystone species whose feeding habits maintain healthy kelp forests along Pacific coastlines, creating one of nature’s most effective carbon capture systems.
Today, over 25,000 sea otters are found bobbing around kelp forests from California to Alaska, although this represents only a fraction of their historical numbers. The current population recovery demonstrates both conservation success and ongoing challenges that these climate-fighting animals face.
Kelp forests store up to 20 times more carbon per acre than trees on land. When kelp dies and sinks to the ocean floor, it traps carbon in seafloor sediment for about 100 years. Global seaweed forests, including kelp, sequester tens of millions of metric tons of carbon annually in deep ocean waters. This equals the carbon storage of roughly half a million acres of trees.
But these underwater forests face a deadly threat from sea urchins. These spiky, ball-shaped creatures sweep across ocean floors devouring kelp at the base. Left unchecked, sea urchins multiply rapidly and can destroy entire kelp forests before they regenerate.
This creates what marine biologists call “urchin barrens” – underwater deserts where thriving ecosystems once existed. When kelp forests disappear, all the carbon they stored gets released back into the atmosphere. Some regions have lost more than 80% of their kelp coverage in recent decades due to this phenomenon.
Sea otters prevent this ecological disaster through their enormous appetites. These mammals must eat 25 to 30 percent of their body weight daily to fuel their high metabolisms. Few animals on Earth consume this much food relative to their size.
Sea urchins rank among sea otters’ favourite meals, along with clams, mussels, crabs, and barnacles. The otters find sea urchins easy to catch and rich in calories. By eating sea urchins in large quantities, otters keep their populations in check and maintain the sea otter climate impact that protects these crucial ecosystems.
Without sea otters patrolling kelp forests, sea urchin numbers explode. The urchins then graze through kelp like underwater lawnmowers, destroying the base of kelp plants and causing the rest to wash away. They even eat young kelp sprouts as they attempt to establish new growth.
Sea otters and kelp forests developed this relationship over evolutionary time. Otters wrap themselves in kelp fronds when resting or use kelp as anchors while feeding. Groups of 10 or more otters floating together are called “rafts.”
Research shows otters swimming in thick kelp canopies escape shark attacks more easily than those in open water. The kelp provides natural protection, while otters provide population control services.
Marine ecologist James Estes documented this relationship in Alaska during the 1970s. His diving research revealed how kelp forests can become underwater deserts in the absence of sea otters. This discovery highlighted the critical role otters play in marine ecosystems.
Sea otters once ranged from Baja California to Alaska and across to Japan and Russia. The fur trade in the 1800s nearly drove them to extinction. Their incredibly dense fur—the thickest of any animal—made them valuable targets for trappers.
Since the 1980s, most northern sea otter populations have continued to recover, though they remain absent from over 2,000 miles of their historical coastline. In California, a population of about 3,000 southern sea otters, a threatened subspecies, is found off the central coast.
However, recent surveys show concerning trends. The population has continued to decline, with the most recent abundance estimate for southern sea otters being 2,962 in 2019. More recent surveys from 2019 to 2024 have shown steep declines in all of these populations across different regions.
The species’ recovery demonstrates how protecting key wildlife creates cascading benefits for entire ecosystems. Healthy otter populations lead to healthy kelp forests, which in turn result in better carbon storage and more stable marine food webs.
Other marine species also influence ocean carbon storage, although sea otter climate impacts are the greatest. Few have a direct impact comparable to that of sea otters. Whales transport nutrients from deep waters to the surface through their feeding and waste, supporting the growth of phytoplankton that capture carbon. Seabirds transfer nutrients from the ocean to land ecosystems through their droppings, supporting coastal vegetation that stores carbon.
See also: How Scientists are Restoring Kelp Forests
However, sea otters remain unique in their direct protection of kelp forest ecosystems. Unlike other marine mammals that indirectly influence carbon cycling, otters actively maintain the predator-prey balance that keeps kelp forests thriving.
Scientists emphasize that protecting sea otters helps this cycle. Healthy otter populations maintain stable kelp forests even as ocean conditions change. The kelp forests then continue capturing carbon from the atmosphere.
The carbon stored in ocean ecosystems, such as kelp forests, is referred to as “blue carbon.” This represents a crucial but often overlooked component of global carbon cycling. Ocean ecosystems can store carbon for much longer periods than land-based forests.
Kelp forests are valued at $500 billion a year for their ecological and economic benefits. Found along 25% to 30% of the world’s coastlines, kelp forests are the most extensive marine vegetated ecosystems.
Coastal restoration projects increasingly focus on blue carbon ecosystems as climate solutions. Protecting and restoring kelp forests is one of the most effective ways to increase ocean carbon storage rapidly.
Sea otters make these restoration efforts more effective by maintaining ecosystem balance naturally. Their predation prevents the boom-bust cycles that destabilize kelp forest communities.
Sea otters represent one of the clearest examples of how protecting wildlife creates climate benefits. Their story illustrates the interconnected nature of environmental challenges and solutions.
