Ocean animals in parts of Antarctica are facing a food shortage. A new British study finds that a staple of the marine wildlife diet, tiny shrimp-like creatures called krill, has dramatically decreased in abundance since the 1970s.  The researchers link the decline to loss of winter sea ice and possibly global warming.

Krill are one of the most important animals in the Southern Ocean food chain. These tiny shellfish, up to six centimeters long, feed on microscopic sea plants called phytoplankton. In turn, they are consumed by a wide range of ocean animals, including fish, whales, seals, penguins, and some birds. They are also a potentially valuable source of protein for humans.

But the British Antarctic Survey has found a dramatic drop in krill populations in the waters off the Antarctic Peninsula, a region with half of all the Southern Ocean's krill stocks. The agency compared krill records gathered by nine countries since 1926.

"We found in that sector, there was a large scale decline. It was about, very roughly, an 80 percent decrease in krill abundance in the last 30 years," said British Antarctic Survey marine biologist Angus Atkinson.  He is the leader of the krill study that appears in the journal Nature.

Along with decreasing krill stocks, his team found a matching decline in the amount of Antarctic Peninsula sea ice in the winter. They say the reason for this apparent link may be that krill larvae depend on the ice for food and shelter from predators in order to grow into adulthood.

"The krill need to survive the winter period when there is very little food in the water column and at that time, the sea ice is a critical resource for the baby krill to survive the winter," he added.  "That is because there is a carpet of algae attached to the underside of the ice, which acts as a concentrated source of food. The overall decline in winter sea ice seems the explanation."

The British Antarctic Survey notes that global warming appears to be the cause for the sea ice melt. Temperatures in the Antarctic Peninsula have risen by two-and-a-half degrees Celsius in the last 50 years. This is about five times more than the average global temperature rise.

Mr. Atkinson says if krill stocks fall too low, there might be detrimental effects on animals that feed on it.  This is especially true of whales, whose populations already are low because of commercial hunting, now banned by an international whaling moratorium.

"After that rapid depletion of whale numbers, other krill predators such as fur seals increased quite dramatically in abundance," he noted.  "So if whales are going to become reestablished in Antarctica, we imagine they would have to compete with all these other higher predators, and also they will be faced with greater scarcity of krill."

Mr. Atkinson says two recent studies show that the krill decline is already having an impact on some Antarctic penguin species, adversely affecting their foraging patterns and breeding numbers.