Bryozoans make unlikely prophets of doom. Nevertheless, scientists believe these tiny marine creatures, which live glued to the side of boulders, rocks and other surfaces, reveal a disturbing aspect about Antarctica that has critical implications for understanding the impact of climate change.

British Antarctic Survey researchers have found the dispersal of these minute animals suggests a sea passage once divided Antarctica 125,000 years ago. The discovery was made for the ongoing Census of Antarctic Marine Life project and involved comparing bryozoans from the Ross and Weddell seas. These two seas are separated by the west Antarctic ice sheet, one of the planet's largest masses of ice. Bryozoans found in the Ross and Weddell seas should have been fairly different in structure if the sheet had been stable and ancient. The two populations would have slowly evolved in different manners, if the sheet was millions of years old.

But Dr David Barnes and his team discovered that the two populations were almost identical, indicating the two seas must have been connected by a major sea passage in the recent past, around 125,000 years ago. "What we've got is this group of animals that don't disperse very well because the adults don't move at all and the larvae are short-lived and sink, so they find it difficult to get around," says Barnes. "So you're left with this nice signal of where things used to be connected and, in this case, it appears to be a connection between what is now an ice sheet."

The impact of the west Antarctica ice sheet melting sufficiently to let a major sea passage extend through it would have been considerable. A complete collapse of the sheet today would lead to a sea-level rise of between 11ft and 16ft, for example, though the event uncovered by Barnes may only have been a partial one. Nevertheless, the research indicates that the great ice sheet, once thought to be impregnable, is really highly vulnerable.