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Alaska sea otters may play unlikely role in climate change scenario

Ben Anderson
Tania Larson/USGS photo

A new study conducted by California, Washington and Alaska researchers finds that the Alaska sea otter -- perhaps best known for its soft fur and ridiculous cuteness -- may have surprising implications for global climate change. In the process, the study suggests that predation of plant-eating wildlife may be another key in the combat against rising carbon dioxide levels in Earth's atmosphere.

The research examined sea otters' impact on kelp forests from Southeast Alaska to the Aleutian Islands chain far to the west over the past 40 years. Researchers found that in areas where sea otters flourished, the density of kelp -- and thus, the amount of atmospheric carbon dioxide that the kelp could absorb -- was much higher than areas without otters.

The reason? Sea otters love to eat kelp-munching sea urchins.

"When sea otters are present, urchins seek refuge in rock crevices and subsist on kelp detritus," the study said. "In the absence of sea otters, urchins often adopt a mobile feeding strategy of grazing on living kelp, thus reducing kelp density and kelp bed distribution."

Basic biology would suggest that plants often perform better in an ecosystem with fewer herbivores when mitigated by predation. But the recent study provides some solid numbers on exactly how much impact sea otters can have on kelp growth and, consequently, carbon emissions.

The study acknowledges that sea otters are just one predator, and kelp just one type of aquatic plant life. But the implications of the study could expand to other populations. The researchers also noted that the impact of sea otters on global carbon levels is "not surprisingly, very small, as is the case for almost all other particular species and ecosystems."

That doesn't mean the numbers aren't significant, though. The research estimates that the saved carbon emissions could be worth between about $200 million and $800 million on the European Carbon Exchange, a commodities market where businesses can purchase credits allowing them to produce a certain volume of emissions.

The researchers suggest the revenue could be used to compensate losses to shellfisheries, which often compete with sea otters due to the mammals' fondness for shellfish. A National Parks Service study examined similar sea otter populations and the effect on seafood ecosystems. 

Meanwhile, Alaska sea otter populations are going through natural changes of their own. In Southeast Alaska, sea otter populations have grown steadily since being reintroduced in the 1960s. Other populations, particularly in Southwest Alaska, have seen significant declines in population in recent decades, perhaps attributable to killer whale predation. Another otter population in California has suffered from an increase in shark attacks in recent years.

So the takeaway from the most recent study isn't a major one, but it does suggest that regions attempting to manage their carbon emissions may want to look at game management as one facet of their plan -- or perhaps those wanting to implement game management programs should also consider carbon emissions.

The study was published Friday in Frontiers in Ecology and the Environment. It was co-authored by researchers from the University of California-Santa Cruz, San Diego State University, University of Washington and Brenda Konar, a professor of marine biology at the University of Alaska Fairbanks.

Contact Ben Anderson at ben(at)alaskadispatch.com