Antarctic Mega-Iceberg Suffocates Seals
Discovery.com, May 27, 2008
Weeks after the controversial listing of polar bears as threatened species, new research graphically demonstrates how changes to polar ice can devastate local animals.
The findings of a grim new study illustrate the direct, and often immediate, effects that climate change can have on the physiology, behavior and survival of wild species.
An Iceberg the Size of Rhode Island
In 1998, ecologist and evolutionary biologist Terrie Williams of the University of California at Santa Cruz and her team began a study on Weddell seals in Antarctica.
Three years later, an enormous iceberg detached near Antarctica's McMurdo Sound. According to Williams and her colleagues, the event was caused by global warming, which has likely been melting and weakening ice at the poles.
The 4,200-square-mile iceberg -- dubbed B-15 -- drifted westward and lodged on nearby Ross Island. The lives of countless animals would soon forever change.
Seals Struggle for Breathing Room
"Our first clue that there was a problem was that the seals were not returning to their usual pupping areas, and that there were fewer seals even later in the season," Williams told Discovery News.
She and her colleagues noticed that the ice around Ross Island did not experience its usual "break-out" that year. Normally the ice thaws, creating thinner areas where diving seals can carve breathing holes in the ice shelf. Instead, the presence of B-15 thickened the surrounding ice.
"We started out with three feet of ice and were up to a nine feet thickness" by 2002, the last year of the study, Williams said.
Filming both above and below the thickened ice, Williams and her colleagues observed seals lining up to breathe at the few holes they were able to make with their front canine teeth. Lacking the energy to swim further, fights ensued in the lines, with animals lashing out at each other for access to air.
Williams explained that after B-15 dislodged, there were 80 miles of ice between McMurdo and the open ocean.
"Weddell seals can only swim four miles under ice before they have to come up to breathe, so you can see the problem," she said.
Physiological Systems Overtaxed
The researchers measured the oxygen consumption of seals that managed to surface, and by analyzing the underwater video, calculated the energy cost of each stroke the seals made during dives.
After comparing these calculations with prior data on seals diving under normal conditions, the researchers found that the new environment simultaneously increased the seals' need for oxygen and reduced their access to air.
Since seals dive to hunt, most were unable to catch enough prey to sustain themselves and their pups.
The findings were recently presented at the Experimental Biology 2008 symposium in San Diego.
"Perhaps the most difficult (to observe) were the abandoned pups. The first rule as a biologist is to let nature take its course -- but is this truly nature when global warming due to human perturbation has instigated the event?" Williams said. "It was exceptionally difficult to walk away from crying pups, knowing that the ice conditions likely cause their mothers to leave."
An Even Longer March for Penguins
Seals weren't the only victims of the B-15 break-off. As fans of the popular film "March of the Penguins" know, the flightless birds must travel long distances to feed at sea before returning to their chicks.
After the drifting iceberg thickened the ice surrounding Ross Island, the researchers observed Adelie penguins struggling to complete a trek that is arduous even under normal conditions.
"With the ice edge so far away it was an impossible travel [a long] distance, so many made a one-way trip and abandoned their nests," Williams said, adding that other biologists in the region reported that many of the nests "failed."
Other Affected Animals
Hannah Carey, past president of the American Physiological Society and a professor of comparative biosciences at the University of Wisconsin School of Veterinary Medicine, told Discovery News that the new research is "compelling" and "may represent one of the best links we have between climate change and the physiology of individual animals, particularly for Antarctic vertebrates."
She said evidence has been mounting that climate-related effects have been disrupting hibernating animals, fish populations, amphibians and other groups, but little work has been done on the physiological impacts to individual animals, and the implications these have for survival of adults and their young.
Carey also said the new research demonstrates how a warming event at the poles can actually lead to ice thickening in other regions, illustrating how "climate change [impacts] on animals can be less predictable and more variable than we may have thought."
James Hicks, professor of comparative and evolutionary physiology at the University of California at Irvine, echoed Carey's comments.
"In a period where global climate change is occurring, scientific studies that investigate the interactions of physiology, behavior, ecology and the physical environment are needed now more than ever," he said. "These types of studies will help us predict how environmental changes may influence animal populations and contribute to our making informed decisions about conservation efforts."
In Human Hands
Both Hicks and Williams hope greater emphasis will be placed on animal physiology studies in the future, as a means of understanding how global environmental challenges can impact animals, including humans.
Williams, however, said the best preventive action "is to get people to recognize the domino effect of human impacts."
"Who could have imagined that driving a car in the U.S. could result in a Weddell seal pup freezing to death in the Antarctic?" she said. "But it did."