Bacteria Diet Controls Mercury Levels in Seabirds

Declining fish stocks near the surface of the British Columbia coast have shown the scientific community an unexpected advantage: levels of mercury in seabirds located in the area have remained relatively stable for the past 50 years because they have had to feed in areas with more sulfate-reducing bacteria that could control mercury levels in organisms.

Researchers from McGill University and Environment and Climate Change Canada have published a paper in Environmental Science and Technology where they detailed how collected seabird eggs along the Pacific coast of Canada for the past 47 years documented a decline in mercury levels for several seabird species. They were able to trace the decline to a switch in diet from high-sulfate, mercury-rich fish to low-sulfate, mercury-poor fish.

The researchers also used isotopic tracers called stable isotopes that revealed seabirds feeding in areas rich in sulfate had high levels of mercury. The seabirds in the Salish Sea of British Columbia switched from fish that live near the surface, to bottom fish since the population of forage fish living close to the surface had dwindled.

"Wildlife are impacted by many different stresses," explained Dr. Kyle Elliott, the lead author of the study who is an Assistant Professor from the Department of Natural Resource Sciences at McGill University. "More predators, dwindling fish stocks and mercury pollution are just some of the variables impacting seabird populations. Fortunately, we found that the level of sulfate-reducing bacteria explained much of the variation in mercury, suggesting that bacteria provided a sort of buffer to variation in mercury within the environment."

Monitoring different seabird species such as cormorants and petrels and their role in the mercury and sulfur cycle would allow scientists to also monitor changes in various parts of the ocean, specifically keeping a close eye on the way mercury moves from human industry into the food chain that leads to seabirds.

"We are becoming increasingly aware that bacteria play an important role in the health of marine ecosystems," concluded Elliott. "Recent studies have shown that wildlife need healthy microbiomes to power long-distance migration. What we discovered was that sulfate-reducing bacteria also control mercury levels. Clearly, what is happening at the base of the food web reverberates up to the top of the food web."