Seeds and plants accidentally brought to Antarctica by tourists and scientists may introduce alien plant species which could threaten the survival of native plants in the finely balanced ecosystem.

Invasive alien plants are amongst the most significant conservation threat to Antarctica, especially as climate change warms the ice continent, said a report in the Proceedings of the National Academy of Sciences Journal published on Tuesday.

More than 33,000 tourists and 7,000 scientists visit Antarctica each year by ship and aircraft, and a two month survey of visitors has found that many are carrying plant seeds picked up from other countries they have already visited.

The study vacuumed travelers' pockets, trouser and sleeve cuffs, shoes and inside their bags, and used tweezers to pry out accidentally hidden seeds. On average each person checked had just 9.5 seeds in clothing and equipment.

"The people that were carrying the most had lots and lots of seeds. They really were substantial threats," said Dana Bergstrom, from the Australian Antarctic Division.

"When we take things in through hitchhiking then we get species which are competitive. The plants and animals there are not necessarily competitive, so there's a good chance... we'd start losing various precious biodiversity on the (Antarctic) continent," Bergstrom told Reuters.

Amongst the alien species discovered were the Iceland Poppy, Tall Fescue Velvet grass and Annual Winter Grass -- all from cold climates and capable of growing in Antarctica.

The Antarctic Peninsula, where most tourists travel, is now considered a "hot spot" on the frozen continent and the warmer the climate, the easier for seeds to propagate.

"The peninsula is warming at some of the greatest rates on the planet," said Bergstrom.

The study, the first continent-wide assessment of invasive species in Antarctica, surveyed about 1,000 passengers during 2007-2008, the first year of the International Polar Year, an international effort to research the polar regions.

It has taken almost three years to identify the seed species and their effects on the icy continent.

Bergstrom said the one alien seed that had gained a foothold is Annual Winter Grass. It is a substantial weed in the sub-Antarctic and is on the Antarctic island of King George. It has also made its way to the tail part of the Antarctic continent.

"That's just one example of the weeds we picked up and a population of it has just been found in the last couple of seasons," she said.

Annual Winter Grass grows very well in disturbed areas like seal and penguin areas, and could propagate amongst the slow growing mosses around those colonies.

"If it got into those areas in the peninsula it would have the potential to overrun things," Bergstrom said.

(Editing by Elaine Lies)

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