Antarctica on alert for alien invaders

"It has been isolated by the southern ocean -- people are starting to break that barrier," she said. New species are getting in partly because visitors' clothes often contain seeds, spores or insect eggs.

So far, invaders have bridgeheads on Antarctic islands ringing the continent, which have been getting warmer in recent decades. Among the most damaging were reindeer on South Georgia and rats and cats on Macquarie Island, Bergstrom said.

Elsewhere in Antarctica, grass was found growing under a Japanese research hut. Invasive plants were found near a Russian station and a wide variety of fungi near an Australian station.

People are acting to try to stem the invasion, even as visitor numbers rise.

"Our flowers are all plastic. We are not allowed to bring in any living thing," said Atle Markussen, head of the Troll scientific research station in a sector claimed by Norway, pointing to a vase of fake red roses on the canteen table.

"The restrictions about alien species are very strict," he said in the base, set amid jagged mountains that look like the homes of fabled Troll giants.

Temperatures during a recent summertime visit were about minus 10 Celsius (14 Fahrenheit) -- far too cold for roses.

Even around Troll, on the edge of mountains 250 km (155 miles from the sea, tens of thousands of Antarctic and snow petrels thrive. Four species of mite, for instance, have been found in recent years and lichen clings to some rocks.

SNOW PETRELS