"The whole food web could shift," Marianne Moore, a biology professor at Wellesley College in Massachusetts and one of the authors of the paper, said in an interview. The frigid lake, which holds 20 percent of the world's freshwater, boasts 2,500 species, most of them found nowhere else, such as the world's only exclusively freshwater seal.

In potentially bad news for that animal, the paper found that the lake's annual days of ice cover had fallen an average of 18 days over the last 100 years and could drop two weeks to two months more by the end of the century.

The findings could foreshadow the vulnerability of smaller lakes to global warming because Baikal's great volume of water had been thought to protect it from rising temperatures, the paper said.

Moore said Baikal's seal, which raises its pups on the ice, could suffer because the animal has several onshore predators. If ice caves the pups are raised in melt, Asian crows could also eat the pups, she said.

Changes in the food cycle have already been seen. Numbers of multicellular zooplankton, which normally live in warmer waters, have increased 335 percent since 1946, while numbers of chlorophyll have risen 300 percent since 1979, it said.