Bacteria control levels of dangerous pollutant in seabirds

Mercury levels in cormorants and petrels stable over past 50 years

Date: December 16, 2016

Source: McGill University

Researchers have discovered that levels of mercury in seabirds off the coast of British Columbia have remained relatively stable over the past 50 years. This might appear to be good news, but it is due to a decline in fish stocks near the surface which has forced seabirds to feed in areas where there are more bacteria (known as sulfate-reducing bacteria) which control the levels of mercury.

Although tiny, bacteria can be very important -- try to make yogurt or miso soup without them. Now, researchers at McGill University and Environment and Climate Change Canada have discovered that bacteria play an important role in determining the health of birds at the top of the food web. By using isotopic tracers called stable isotopes, researchers showed that seabirds feeding in areas rich in sulfate (a chemical that is an important food for sulfate-reducing bacteria that help break down organic matter) had high levels of mercury. Those same sulfate-rich areas were favoured by the sulfate-reducing bacteria which produce methylmercury, a toxic substance which is then taken in by the fish that eat them and eventually by the seabirds that feed on the fish.

The authors of a recent paper published in Environmental Science and Technology used seabird eggs collected along the Pacific coast of Canada over 47 years, and archived by Environment and Climate Change Canada in Ottawa. They documented a decline in mercury levels for several seabird species over 47 years. However, they traced that decline to a dietary switch from high-sulfate, mercury-rich fish to low-sulfate, mercury-poor fish. Thus, there was no overall change in mercury levels.

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Alaska's shorebirds exposed to mercury

Date: July 13, 2016

Source: Central Ornithology Publication Office

Shorebirds breeding in Alaska are being exposed to mercury at levels that could put their populations at risk, according to new research from The Condor: Ornithological Applications.

Thanks to atmospheric circulation and other factors, the mercury that we deposit into the environment tends to accumulate in the Arctic. Mercury exposure can reduce birds' reproductive success and sometimes even be lethal. Shorebirds may be particularly vulnerable because they forage in aquatic environments where mercury is converted into methylmercury, its most dangerous form. Marie Perkins of the Biodiversity Research Institute (BRI) and her colleagues investigated the level of mercury in Alaska's shorebirds and found that some birds breeding near Barrow, at the state's northern end, have mercury concentrations upwards of two micrograms per gram of blood.

"These species already face a lot of tough new challenges, from climate change to disappearing stop-over habitat, so throwing a neurotoxin in the mix that can reduce reproductive success is likely to harm their populations," according to Dan Cristol of the College of William & Mary, an expert on mercury in birds who was not involved with the new study. "The mercury concentrations reported in this paper are likely to reduce reproduction, but not catastrophically, based on what we know from other species. What may be even worse, though, is that these mercury levels probably spike when they leave the breeding grounds and start burning their reserve fuel, making their already arduous continent-jumping trips even harder."

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Mercury contamination threatens Antarctic birds

Date:

April 10, 2014

Source:

CNRS

Summary:

Mercury contamination in the Antarctic and Subantarctic affects bird populations, reveal researchers. The scientists monitored skuas in Adélie Land and the Kerguelen Islands for ten years and showed that, when these seabirds exhibit high mercury levels in their blood, their breeding success decreases. This is the first time that toxicological measurements have been combined with a population study carried out over such a long period in the Antarctic and Subantarctic.

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