April 12, 2011

Melting Ice Threatens Penguins’ Primary Food Source

Young penguins in the Antarctic may be dying for lack of food, as melting sea ice reduces the numbers of small fish they consume as their primary food source, according to a new study published Monday in the Proceedings of the National Academy of Sciences (PNAS).

The researchers found that just 10 percent of baby penguins tagged are returning in two to four years to breed, a drop of 40-50 percent since the 1970s.

The study indicates that species often considered likely "winners" of climate change conditions, such as large-scale ice melting, might actually be the most vulnerable to the impacts.

The two penguin species in the study rely on small crustaceans called krill as their primary food source.  A previous study of krill in the Southern Ocean suggests that their abundance has dropped as much as 80 percent since the 1970s.

"For penguins and other species, krill is the linchpin in the food web. Regardless of their environmental preferences, we see a connection between climate change and penguin populations through the loss of habitat for their main food source," said Dr. Wayne Trivelpiece, lead author and seabird researcher of the National Oceanic and Atmospheric Administration's (NOAA) Antarctic Ecosystem Research Division.

"As warming continues, the loss of krill will have a profound effect throughout the Antarctic ecosystem."

A 30-year field study of Ad©lie (ice-loving) and chinstrap (ice-avoiding) penguins shows that populations of both species in the West Antarctic Peninsula and Scotia Sea have declined by averages of 2.9 and 4.3 percent per year, respectively, for at least the past decade.  Some colonies have fallen by more than half.

Lack of an abundant supply of krill has been particularly hard on fledgling penguins, which must learn where to locate and how to catch the prey on their own, having never been at sea before.

The current study suggests that fewer young penguins are surviving this transition to independence today than in previous years when these crustaceans were much more abundant.

Although chinstrap penguins avoid feeding in icy habitats, sea ice provides the necessary environment for krill to reproduce.  Rising temperatures and reductions in sea ice have made conditions unfavorable to sustain ample populations of this food source.

The researchers suggest that fishing for krill and increased competition among other predators also have made them less available to penguins.

"Penguins are excellent indicators of changes to the biological and environmental health of the broader ecosystem because they are easily accessible while breeding on land, yet they depend entirely on food resources from the sea. In addition, unlike many other krill-eating top predators in the Antarctic, such as whales and fur seals, they were not hunted by humans," said Dr. Trivelpiece.

"When we see steep declines in populations, as we have been documenting with both chinstrap and Ad©lie penguins, we know there's a much larger ecological problem."

Ad©lie penguins, which feed in icy habitats, are also declining due to food shortages and shrinking habitat.  However, they differ from chinstrap penguins in that they have breeding populations outside of the western Antarctic, which makes them less vulnerable to warming in the Antarctic Peninsula region by comparison.

The study, funded in part by the Lenfest Ocean Program, was published online Monday in the Proceedings of the National Academy of Sciences. 


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