It's not the type of predator that turns up in nature shows. But researchers in California say fog—yes, fog—poses a threat to mountain lions, reports Smithsonian. The reason? The marine fog in the Santa Cruz Mountains carries mercury, and that neurotoxin settles on the ground and works its way up the food chain. For example, it gets absorbed by lichen, which is eaten by deer, and the deer are then eaten by mountain lions. In the study published in Nature, scientists found that local pumas had roughly three times the level of mercury as their inland counterparts. The mercury levels in the fog itself aren't high enough to pose a threat to humans, say the UC Santa Cruz researchers in a press release. But they say the risk to mountain lions and other "terrestrial mammals" is real because mercury concentrations increase as they go up the food chain.
"Fog is a stabilizing medium for methylmercury," explains lead author Peter Weiss-Penzias. "Fog drifts inland and rains down in microdroplets, collecting on vegetation and dripping to the ground, where the slow process of bioaccumulation begins." Mercury is a naturally occurring element, but it also gets released into the environment through mining and coal-fired plants. The scientists studied 94 coastal mountain lions, and they averaged mercury concentrations of 1,500 parts per billion, compared to 500ppb for their inland cousins. Generally, these levels aren't lethal (though the mountain lion with the highest level was found dead), but the increased mercury could take a toll on reproduction. One of the study's big-picture conclusions: "As global mercury levels increase, coastal food webs may be at risk to the toxicological effects of increased methylmercury burdens." (Read more mountain lion stories.)