How important are jellyfish to the diets of Adélie penguins in the Antarctic?
That’s the question Pew marine fellow Yan Ropert-Coudert, director of research at France’s Centre d’Études Biologiques de Chizé, Centre National de la Recherche Scientifique, is seeking to answer. Along with colleagues from the National Institute of Polar Research in Japan, he decided that the best way to know about the penguins’ diet was to watch them eat.
Typically, Adélie penguins rely on a diet of krill, a small, shrimplike animal. But a decline in krill and an increase in jellyfish in the Southern Ocean prompted the researchers to begin temporarily attaching miniature cameras to the penguins’ lower backs so they could review video of the flightless birds as they forage for food.
Antarctic krill play a central role in Southern Ocean food webs and support populations of penguins, fish, seals, and whales. But recent studies have shown that krill are sensitive to ocean warming and acidification and that their numbers may be in decline. Now, gelatinous organisms such as jellyfish, sea salp, and comb jellies have begun to predominate in some of the world’s marine ecosystems. While not as nutritious as krill, they are abundant and easy to catch. So over the past four years, Ropert-Coudert and his colleagues have been trying to determine whether the penguins have changed their feeding patterns to rely more heavily on these plentiful food sources.
This work is part of a larger research effort to use animal-borne cameras, a technique known as biologging, for clues on how top predators in marine ecosystems around the world are responding to changes in their environment—especially when it comes to the availability of food. As the oceans warm, scientists are concerned that changes to the food web, especially in areas such as Antarctica, may force these animals to modify their feeding patterns due to changes in their prey base. Such studies ultimately aim to define areas of ecological significance for marine predators, so these places may be considered for protections in the future.
So to answer the question—Is a shift in feeding patterns happening in the Southern Ocean?—the scientists capture video from the back of a live penguin, which, not surprisingly, isn’t easy to do. To start, the researchers must painstakingly secure about a dozen strips of tape, sticky side up, beneath a patch of feathers on the bird’s lower backs—looping the tape around the feathers to preserve the bird’s plumage. The scientists then wrap the tape around the camera to secure it in place.
Each camera weighs about 7 ounces—anything heavier would impede the birds—and can record video for four to six hours, depending on its battery type. Because this time frame often isn’t long enough to capture the entire feeding trip of Adélie penguins, researchers may only get a glimpse of their activity at sea. So they use their knowledge of penguin feeding activity to program the video to start when the bird will be roughly at its farthest point from the colony, where it typically engages in the bulk of its feeding. To do this, the scientists schedule cameras to start recording at a certain time; some may also be set to activate when the bird reaches a certain depth.
The research takes place during the chick-rearing period, with cameras deployed wherever there is a suitable nest—one where a member of the pair is about to head out to sea to feed. To retrieve the video, the scientists must recover the camera upon the penguin’s return and remove the tape from the bird’s feathers as carefully as they placed it. They then change the camera’s batteries and repeat the process, reusing the device on a new bird. “We follow the rhythm of the penguins, and they just don’t stop!” Ropert-Coudert says.
He and his team suspect that jellyfish and other gelatinous organisms may account for a more substantial portion of the penguins’ diets than once thought. Because these free-swimming animals leave little trace in a penguin’s excretions or stomach contents after digestion, researchers may have missed this source of food in their diets. Alternatively, penguins may increasingly be turning to this food source as gelatinous animals become more abundant and krill stocks decline. The cameras can help the scientists pin down what the animals are eating.
In his Pew marine fellowship, Ropert-Coudert is investigating, among other things, whether the complex gelatinous community in the Southern Ocean could serve as an alternative food source for krill-dependent species such as the Adélie penguins. So far, researchers have found that while jellyfish are a regular part of the penguins’ diet, there is no evidence that this food source is more important than it was before.
Polita Glynn directs the Pew fellows program in marine conservation.