Hungry penguins chase Antarctic's shifting krill

Waddling over the rocks, legions of penguins hurl themselves into the icy waters of Antarctica, foraging to feed their young.

Like seals and whales, they eat krill, an inch-long (2.5 cm) shrimplike crustacean which forms the basis of the Southern Ocean food chain.

But penguin-watchers said krill are becoming scarcer around the western Antarctic peninsula, under threat from climate change and fishing.

"Krill is the power lunch of the Antarctic. It's a keystone species for everybody," said Ron Naveen, leader of the US conservation group Oceanites, as penguins squawk on the rocks behind him.

In a vast ocean whose water flows influence the whole planet, krill rely on the sea ice to protect them and provide algae to feed them while they grow.

The ice is getting scarcer.

The peninsula has warmed by 3 degrees Celsius over the past half-century, according to groups such as the World Wildlife Fund.

Scientists suspect that shifting ice patterns are effecting penguin populations.

"The interaction between warming temperatures, increasing ocean acidity, and of course to some extent, although it's not clear yet, an interaction with the fishing industry fishing for krill, will put pressure on predator populations that are mostly krill feeders," such as penguins, said Steven Chown, a biologist at Monash University in Australia.

The International Union for Conservation of Nature said penguins and krill are both potentially threatened by future climate change.

And species such as penguins are also threatened by krill-fishing, it said.

"Krill fishing may be occurring too close to where the penguin breeding colonies are," Naveen said. "And perhaps more importantly, areas where the penguins are foraging."