Wildfires are a mixture of good and bad. They help regenerate plant growth, and clear out old sticks, logs and bark. At the same time they produce environmental pollutants, known as polycyclic aromatic hydrocarbons, or PAHs. These are left over when something isn't burned completely, like, cooking a steak over an open flame, for example. After a wildfire, these PAHs wash into streams and, eventually, out to the ocean. 

Lizabeth Bowen, a biologist with the U.S. Geological Survey has been studying the effects of the fallout from fire in several species. In 2008, just weeks before a planned otter capture survey, two major fires burned near the coast of Central California: the Basin Complex fire and the Chalk fire. 

One year later they re-captured otters in the same locations, allowing them to compare gene expression between the two conditions. When PAHs were in high concentration, following a fire, sea otter's immune system was suppressed, they found.  The effect was similar to an oil spill. With a suppressed immune system, sea otters are less able to fight other pollutants or pathogens in the environment. 

"There's really nothing we can do to protect them [from wildfires]," says Bowen, "but it’s important information to know. When you start to manage a population, species or area, you need to think about what stressors you can mitigate when you have a wildfire come in."

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