Nov. 3 (Bloomberg) -- The loss of sea ice in Antarctica brought on by global warming may be causing a decline in numbers of the crustacean krill, posing a risk to other marine wildlife that feed on it, scientists said in the journal Nature.

The amount of krill in the southwest Atlantic has fallen by about 80 percent since 1979, correlating with a drop of at least 30 days in the duration sea ice lasts in the crustacean's main breeding ground in the region studied, said the study's lead author Angus Atkinson of the British Antarctic Survey.

``Open water is bad for krill because there is less food,'' Atkinson said in a telephone interview from Cambridge, referring to algae upon which the crustacean feeds. ``The food is on the sea ice, so there's less time for the krill to feed'' with the ice melting earlier.

Changes in the krill population ``have profound implications for the Southern Ocean food web,'' the scientists said in the study. ``Penguins, albatrosses, seals and whales have wide foraging ranges, but are prone to krill shortage.''

Other scientific studies have shown that a drop in krill population has ``clearly adverse'' effects on species that feed on it, such as fur seals, black-browed albatrosses, and gentoo and macaroni penguins, Atkinson said. The loss of krill is also a potential threat to fish, he said.

The scientists studied an area of the southwest Atlantic Ocean between the latitudes of 30 and 70 degrees west, a region where as much as 71 percent of the Southern Ocean's krill are found. The temperature of the Western Antarctic peninsula, adjoining the study area, has risen by about 2.5 degrees centigrade over 50 years, Atkinson said.

`Key' Spawning Area

``The western Antarctic Peninsula is one of the world's fastest warming areas, and, atypically for the southern ocean, winter sea-ice duration in this sector is shortening,'' the team said. ``Key spawning and nursery areas of krill are thus located in a region that is sensitive to environmental change.''

While the decline in sea ice is the ``most plausible'' reason for a drop in the krill population, other factors which may affect the organism include an increase in predation, and the effect of warmer temperatures on spawning, Atkinson said. More research is needed to establish how other factors affect krill, before any proposals can be made on how to deal with the decline, he said.

Krill, whose Latin name is Euphausia Superba, is a shrimp- like crustacean that grows to a length of about 6 centimeters (2 inches) and can live for five to six years.

The government-funded British Antarctic Survey has an annual budget of about 40 million pounds ($71.8 million), and operates five research stations, two research ships and five aircraft in and near Antarctica. It has nine research programs.

To contact the reporter on this story: Alex Morales in London at amorales2@bloomberg.net.

Last Updated: November 3, 2004 13:00 EST