How important are jellyfish to the diets of Adélie penguins in the Antarctic?
That’s the question Yan Ropert-Coudert, director of research at the Chizé Centre for Biological Studies in Villiers-en-Bois, France, and his colleagues from the National Institute of Polar Research in Japan are determined to answer. And to do that, they are outfitting penguins with video cameras to track the birds as they forage for food.
For the past four years, prompted by a decline in krill and an increase in jellyfish in the Southern Ocean, researchers have been temporarily attaching miniature cameras to the animals’ lower backs—taping them carefully to avoid disrupting their plumage—to see if the penguins are seeking out jellyfish and other gelatinous organisms as prey. Typically, the flightless birds rely on a diet of krill, a small, shrimplike crustacean.
Using a live penguin to capture video is not easy. The videos often don’t last long enough to record the entire feeding trip of Adélie penguins, and researchers might get only a glimpse of their activity at sea. Using their knowledge of penguin foraging activity, however, the researchers program the technology to begin capturing footage when the bird will be roughly at its farthest point from the colony, where they typically engage in the bulk of their feeding. Foraging trips last from a few hours in years of good food availability to several weeks in particularly bad years, and are shorter when the birds are feeding very small chicks.
Ropert-Coudert and his team suspect that jellyfish and other gelatinous organisms may account for a more substantial portion of the penguins’ diets than once thought. Researchers might have missed this source of food in their diets because the free-swimming jellies leave little behind in penguins’ feces or stomach contents after digestion. Alternatively, the penguins may be increasingly turning to gelatinous invertebrates as they become more abundant and krill declines due to climate change and other factors.
As the climate changes and oceans warm, scientists are concerned that changes to the food web, especially in areas such as Antarctica, might force organisms to change their feeding patterns. Antarctic krill play a central role in Southern Ocean food webs and support populations of penguins, fish, seals, and whales. Recent studies have shown, however, that krill are sensitive to ocean warming and acidification and that their numbers might be in decline. By contrast, gelatinous organisms such as jellyfish, sea salps, and comb jellies have begun to predominate in some marine ecosystems in the world. Although not as nutritious as krill, they are abundant and easy prey for most predators.
In his Pew marine fellowship, Ropert-Coudert and his team are investigating, among other topics, whether the complex gelatinous community in the Southern Ocean could serve as an alternative food source for krill-dependent species such as Adélie penguins. So far, their research has found that jellyfish are a regular part of the penguins’ diet, but they have no evidence yet that these organisms are more important than they were before.
Polita Glynn is a project director for environmental research and science with The Pew Charitable Trusts.