Sea ice critical for rests during long foraging treks
By Summit Voice
SUMMIT COUNTY — Climate-related shifts in ice around Antarctica have already been implicated in the disappearance of at least emperor penguin colony, but researchers have not been sure exactly how sea ice figures in to their life cycle.
In a new study, researchers show how the birds use sea ice to rest during long foraging periods. The life cycle of the emperor penguins takes place in an exquisite balance with the rhythms of ice formation. Courtship, egg laying and incubation occur during winter, followed by hatching, brooding and crèche formation during spring and early summer. Both parents tend the chicks until they fledge, generally in late spring and early summer (November and December), when the ice breaks up into floes that drift with the wind and currents.
Unlike other species, like Adelie penguins, emperor penguins spent much more time diving for food, and only used about 30 percent of their time at sea to take short breaks to rest on sea ice. The birds did not travel for long distances on the ice, or use it for other activities. The study also suggests that these short rest periods on sea ice may help the penguins avoid predators such as leopard seals.
Though sea ice conditions are known to affect penguin populations, the relationship between ice levels and penguins’ foraging has been unclear because of the difficulties of tracking the birds at sea.
Scientists from the Woods Hole Oceanographic Institution recently took a close look at a long-studied colony in Terre Adélie, concluding that the number of breeding pairs at the colony could drop by 80 percent by the end of the century.
The researchers emphasized that their projections contain large uncertainties, because of the difficulties in projecting both climate change and the response of penguins. However, almost all of their computer simulations pointed to a significant decline in the colony at Terre Adélie, a coastal region of Antarctica where French scientists have observed penguins for more than 50 years.
“Our best projections show roughly 500 to 600 breeding pairs remaining by the year 2100,” says lead author Stéphanie Jenouvrier, a WHOI biologist. “Today, the population size is around 3,000 breeding pairs.”
She said another penguin population on the Dion Islets close to the West Antarctic Peninsula, has disappeared, possibly because of a decline in Antarctic sea ice.
The new research represents a major collaboration between biologists and climate scientists to assess the potential impacts of climate change on a much-studied species.
At nearly four feet tall, emperors are the largest species of penguin. They are vulnerable to changes in sea ice, where they breed and raise their young almost exclusively. If that ice breaks up and disappears early in the breeding season, massive breeding failure may occur, Jenouvrier says.
Disappearing sea ice may also affect the penguins’ food sources. They feed primarily on fish, squid, and krill, a shrimplike animal that feeds on zooplankton and phytoplankton that grow on the underside of ice. If the ice goes, Jenouvrier says, so too will the plankton, causing a ripple effect through the food web that may starve the various species that penguins rely on as prey.
The study was published November 21 in the open access journal PLOS ONE by Shinichi Watanabe and colleagues from Fukuyama University in Japan. It describes emperor penguin foraging behavior through the birds’ chick-rearing season.