Mercury in Oceans: Elephant Seals Shed Mercury During Molting Season

Elephant seals accumulate high concentrations of mercury from the marine species they feed on. In return, these large seals shed serious amounts of mercury during their molting season. Researchers from the University of California - Santa Cruz found that this, previously unknown, source significantly contaminates oceans.

"Many studies have looked at biomagnification up the food chain, and we took that a step further to see what happens next. Mercury is an element, so it never breaks down and goes away--it just changes forms," Jennifer Cossaboon, first author and graduate student in environmental health at San Diego State University, said in a news release. Cossaboon led this study as an undergraduate at UC Santa Cruz.

Biomagnification is when methyl mercury is absorbed and accumulated in marine organisms, and becomes increasingly toxic as it moves up the food chain. This affects top predators, such as the elephant seals, who can accumulate one to 10 million times more mercury than that found in surrounding seawater.

Russell Flegal, a microbiology and environmental toxicology professor at UC Santa Cruz, performed previous studies that found increased mercury levels in mussels around large seal and sea lion populations at Año Nuevo and San Miguel Island.

"At that time, we didn't have the analytical instruments to detect mercury at the concentrations found in seawater, so we used mussels, which filter seawater, as sentinel organisms," Flegal said in a statement. "In the new study, we were able to look at seasonal changes in the water, and during the elephant seal molting season the levels of methyl mercury really took off."

According to the recent study, methyl mercury concentrations of seawater around Año Nuevo are twice as high during the breeding season and 17 times higher during molting season. During the annual molting time, the seals' entire outer layer of skin and hair, known as pelage, comes off. During this molting season, the researchers measured extremely high levels of methyl mercury in the water, signifying that the pelage is the main source.

The researchers further noted that they are unsure what these concentrations mean for the elephant seals and how their findings can be applied to other species.

Their study was recently published in the journal Proceedings of the National Academy of Sciences.

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