What the Black-Legged Kittiwake can teach us about mercury
A study showing that high levels of mercury might prevent a Svalbard bird from breeding could have rippling implications for other large mammals, including humans, that live in the mercury-rich Arctic.
In the decade that scientists have followed the migrations of the black-legged kittiwake, a grey-winged polar bird that breeds each summer on the ice-capped cliffs of Svalbard, a surprising pattern has emerged: Each year a number of birds make the 4,000 km flight from Newfoundland, build their nests and produce…nothing. No eggs, no young—a long journey for sure without the promise of offspring.
After observing the Kittiwake, Sabrina Tartu, a doctoral student at the University of La Rochelle studying eco-physiology, developed a theory. The kittiwakes, like most arctic mammals, have been ingesting increasingly amounts of mercury from the element-saturated environment. Could the high concentrations of mercury in Svalbard waters and soils be, not just infecting the species but also actively preventing them from bearing young?
The results of Tartu's study could have big implications for the large mammals—including humans—who live in Arctic regions.
Buried in glaciers and swirling in the oceans, the Arctic contains some of the highest concentrations of mercury on the planet—and growing: Each year the Arctic Ocean spews about 75 tons of mercury south, while hoarding 110 tons into sediment collections. In water mercury can become particularly toxic, uniting with oceanic bacteria to become metylmercury, a neurotoxin.
Natural deposits of mercury are relatively sparse, but human created emissions—fromcoal burning, mining and other industrial activities—now make up over half of the element’s global supply. Scientists disagree on why so much mercury is housed in one of the world’s most remote places, especially when over 90 percent of the supply originates from man, according to the Arctic Monitoring and Assessment, a research program of the Arctic Council.
And Mercury never goes away. Like a festering dinner guest, mercury only becomes more concentrated and toxic as it spreads through the food chain: from plankton to fish to seals and large marine life to predators, such as the mercury-inebriated polar bear, and humans.
To test her reproductive theory, Tartu’s laboratory on Ny-Alesun, Svalbard sampled blood from just over 100 birds in early June, before their breeding period. They tested for mercury levels and then monitored the nests of the sampled birds every two days to see if they reproduced. (Kittiwakes are monogamous, repetitive creatures, which use the same nest year after year, making the scientist’s task easy.)
To their surprise, the researchers found a strong relationship between mercury and reproduction: The birds that contained the highest levels of mercury unilaterally failed to breed.
To better understand the interaction between Mercury and the bird’s endocrine system the researchers staged a secondary study. They injected the birds with exogenous GnRH, a hormone that activates the pituitary gland, and monitored the subsequent release of LH, a sex steroids key for breeding.
They found that in non-breeding birds, LH levels decreased with mercury exposure in males and increased in females. The researchers speculated that mercury might bind to sex steroids, preventing it from smoothly moving to receptors. These results were recently published Biology Letters.
Though studies have shown mercury to have dramatic effects on small marine life, even changing the gender of mollusks in cases of extreme exposure, study of larger animals such as birds is rare and might be more readily applied to human experience.
“We are seeing more and more of this kind of endocrine disrupter,” said Geir Wing Gabrielsen, head of the Environmental Pollutants division of the Norwegian Polar Institute. “You’re talking about cocktails of chemicals that are affecting the body—sometimes even in low concentrations—in disturbing ways.”
In polar-regions, where breeding is a carefully balanced mechanism of survival, any disruption to the endocrine system might have dire circumstances for the ecosystem. Kittiwakes, like many arctic mammals, use super-senses to predict the climate, choosing only to breed in warm years when they will have ample access to food for their young. If it’s a cold year, they wait.
“If mercury disrupts this ability to decide if [they] should breed or not, it can become very difficult for the birds to reproduce,” says Tartu.
Scientists expect the effects of Arctic mercury to increase, as climate change releases mercury housed in permafrost, sediments and glaciers.
“Mercury levels in seabirds are increasing and if combined with rapid climate change, we are facing a worst-case scenario,” reads the study.