The marine birds that inhabit Canada’s expansive North, such as the Arctic tern, common eider, and long-tailed duck, are important resources for northern communities. These resilient and often stunning birds are pivotal to the region’s diverse ecosystems and are essential sources of food and feathers (e.g., eiderdown) for northern peoples. A number of studies, however, suggest that Arctic bird species, as well as other animals, are in danger of mercury poisoning.
Recently, Canadian researchers J.F. Provencher, M.R. Forbes, B.M. Braune, and H.G Gilchrest from Carleton University, as well as M.L. Mallory from Acadia University studied the effects of mercury on nine different species of marine birds from Canada’s Arctic, including the ivory gull, the black-legged kittiwake, the common eider, the long-tailed duck, and the thick-billed
murre. Birds are generally excellent indicators of ecosystem mercury contamination. This is because mercury affects their nervous system and development pathways, resulting in poor egg quality and reduced brood size — traits that are easy for scientists to record and measure.
Mercury is also harmful to the ecosystem as a whole because in aquatic environments, insoluble mercury compounds, which are not readily taken up by plants or animals, can be converted by bacteria into highly toxic organomercury compounds, such as methyl mercury.
In 2013, the United Nations placed mercury on its list of major concerns to human and ecosystem health. Industrialization and the burning of fossil fuels have increased the rate at which mercury is released to the environment, outpacing the natural rate of mercury removal from the environment.
Overall, the Canadian research team found that the Ivory gull had the highest reported egg mercury levels, whereas the blacklegged kittiwake had the lowest. The scientists believe that the high levels of mercury observed in the birds are related to their diet and position in the food chain.
Mercury moves up the food chain through bioaccumulation. Plants and animals at the bottom of the food chain, such as crustaceans and rodents, are the first to ingest mercury. Animals higher up on the food chain eat bottomlevel animals and are then eaten by animals above them on the chain. At each level, the amount of mercury consumed increases and, thus, the amount of poisoning increases as well. This likely explains why the Ivory gull has more mercury incorporated into its eggs on average than the blacklegged kittiwake — the gull is higher on the food chain than the kittiwake.
This and other studies also suggest that increased environmental mercury levels have altered ecosystem food webs as a whole. The researchers inferred from reported population trends that animals at the top of the food chain are dying off at unexpected rates because of mercury poisoning. Their absence leaves a void at the top of the food chain; thus, animals that were previously out competed may have additional opportunities to obtain resources.
This research has a wide range of significance as increasing mercury levels affect not only marine birds in Canada’s Arctic but many other organisms on the planet. Although there is a concerted effort in North America to decrease mercury emissions, there is less awareness and motivation to do so in Asia where industrialization is rampant. Other research has shown that mercury emissions from Asia spend between six months to two years in the atmosphere, where air currents can carry it across the Pacific Ocean and into Canada’s Arctic.
Unfortunately, while human influences are the main cause of increasing mercury levels, the research team warns that it is far from the only cause of mercury increase. In the Arctic, glaciers and ice caps have served as reserves that store mercury from past emissions. However, as Earth’s climate gets increasingly warmer, these large bodies of ice are melting and releasing mercury into the environment.
Further studies of mercury release in Canada are important for all of us because mercury levels in Canada’s Arctic are among the highest in the world. When comparing their results to earlier studies, the researchers found that Arctic Canada’s birds had higher overall levels of mercury incorporated in their eggs than birds from other parts of the world. Although Canada has a long history of monitoring mercury in the Arctic, it is imperative that we continue to research marine birds and support our northern ecosystems. Investing more effort in protecting these birds and the resources that they provide is a goal that should “fly” with many Canadians.
Max Stone and David Smith
Max Stone is a fourth-year undergraduate student studying Biology at Western University, and is a volunteer science writer in David Smith’s Lab, Biology Department. David Smith is an assistant professor in the Biology Department at Western University. You can find him online at www.arrogantgenome.com.