Science News
Penguins: Loss of Krill
It’s not news that the Antarctic sea ice is disappearing. And with its disappearance, there goes the penguins, too. But a new study, published this week in the Proceedings of the National Academy of Sciences, shows the lack of ice isn’t directly to blame for penguin decline.
Wayne Trivelpiece, lead author of the paper and seabird researcher for NOAA, has been studying the Antarctic penguins—chinstraps and Adélies—for 30 years. He’s witnessed both species decline in the West Antarctic Peninsula and Scotia Sea by respective averages of 4.3 and 2.9 percent per year for at least the last 10 years. Some colonies have decreased by more than 50 percent. Warming temperatures seem the obvious reason for this decline. From the abstract:
This region is also among the fastest-warming areas on the planet, with 5–6 °C increases in mean winter air temperatures and associated decreases in winter sea-ice cover… One hypothesis guiding ecological interpretations of changes in top predator populations in this region, the “sea-ice hypothesis,” proposes that reductions in winter sea ice have led directly to declines in “ice-loving” species by decreasing their winter habitat, while populations of “ice-avoiding” species have increased.
But this hypothesis doesn’t explain the chinstrap population decline—they are the “ice-avoiding” species.
Both the chinstraps and Adélies rely on small shrimp-like creatures known as krill for their survival. A previous assessment of krill in the Southern Ocean suggests that their abundance has declined 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 Trivelpiece. “As warming continues, the loss of krill will have a profound effect throughout the Antarctic ecosystem.”
Science News offers some reasons for the disappearing krill:
Some of that has to do with whales and seals — many of these krill-eating species have resurged since the end of Moby Dick-era hunting. But, Trivelpiece says, the story also comes back to ice. Young krill grow big and fat while hiding under ice masses. Less ice means less krill, and that means both Adélies and chinstraps go hungry.
Penguins may be the canaries in the coalmine, says Trivelpiece. “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. When we see steep declines in populations, as we have been documenting with both chinstrap and Adélie penguins, we know there's a much larger ecological problem.”
Image courtesy of Gilad Rom/Wikimedia