Aliens in Antarctica

It was a summer day in January when Peter Convey pulled up a weed in Antarctica for the first time. The alien plant stuck out among the native species eking out an existence on the rocky debris beneath his feet.

Convey doesn’t know for sure how the intruder, a rugged relative of the ornamental plant gerbera, traveled from its usual home 1,000 kilometers away in Tierra del Fuego. A seed may have drifted in on the wind or hitched a ride on the feather of a bird crossing the Southern Ocean. But Convey suspects that some human unwittingly delivered the species during fieldwork or while touring the remains of a whaling station nearby.

With Antarctica more trafficked by human feet than ever, scientists fear that Convey’s pulled plant and others like it herald a coming invasion. In the same way stink bugs, Asian carp and kudzu have become abundant enough to alter ecosystems across North America, earning the name “invasives,” species entering the Antarctic could multiply and spread. If so, nonnative plants — and even insects — may disrupt the most pristine landscape on Earth.

A handful of foreign creatures, including a particularly hardy kind of grass, have already shown that they’re tough enough to put down roots at the end of the Earth.

“Several nonindigenous species have now gotten a toehold on the Antarctic continent,” says Convey, a polar ecologist with the British Antarctic Survey in Cambridge, England. “Some of these species have already proven to be invasive in other places.”

When the 50 countries signed on to the Antarctic Treaty meet in June, the issue of nonnative species will be on the agenda. Researchers will present findings on potential plant invaders from the first study that counts how many seeds enter Antarctica and identifies hot spots where the seeds could sprout.

Planting red flags

Worrying about immigration in a land mostly covered by ice may seem like a waste of time. But about a third of a percent of the continent is ice-free during the summer, an area almost the size of the Dominican Republic. Microbes, mosses, invertebrates and two species of flowering plant that can tolerate the inhospitable conditions call these bare patches of ground home. Having long lived in isolation, the creatures aren’t used to competing with outsiders.

But isolation, at least from people, is no longer an option. Tourism brings about 33,000 people to the continent each year. Scientists and their support staff add another 7,000. More than 70,000 seeds cling to the shoes, clothing and bags of a single summer’s worth of visitors, say researchers from eight countries who have collected, counted and identified thousands of stowaway seeds. The scientists, who reported the results in March in the Proceedings of the National Academy of Sciences, also checked the places where humans hang out for spots warm enough to nurture these unwelcome seeds.

About half of the tiny passengers come from cold climates to begin with, giving them an edge in Antarctica. Areas near the coast, where the climate is milder than in the continent’s interior, could serve as landing sites, the new analysis reveals. The Antarctic Peninsula, jutting northward from the continent and home to many research stations, stood out as having an especially high risk of invasion. Red flags also popped up along the Ross Sea and the coast of East Antarctica.

Climate change will make Antarctica even more vulnerable in the coming years, particularly on the peninsula, the researchers say. The peninsula’s western coast has warmed faster than most places on the planet — by about 2.5 degrees Celsius since the 1950s. Balmier temperatures raise the odds that would-be interlopers will survive and spread.

Safety precautions could help curb the influx of life, says polar ecologist Kim Crosbie, a coauthor on the new study who is with the International Association of Antarctica Tour Operators in Providence, R.I. Tourists tend to be clean visitors. Before setting foot on Antarctic soil, they are instructed to step in disinfectant, and their clothes are vacuumed. But scientists and the staff manning tourist expeditions are laxer, as revealed in the new seed counts.

“Everyone has a favorite jacket, and there’s a tendency for staff to wear the same gear a lot and not clean it as much,” Crosbie says.

Some areas flagged in the new study have already been infiltrated. An upcoming paper in Conservation Biology reports that an aggressive species of alien grass has appeared outside three scientific research stations on the Antarctic Peninsula.

Poa annua made its Antarctic debut in the 1980s, after having been brought — unintentionally — to a Polish outpost on King George Island. The weedy plant escaped and grew in patches on the island, which is close enough to the mainland to be considered part of Antarctica. Wind then carried seeds 1.5 kilometers away from the station, where the grass sprouted on debris left behind by a retreating glacier.

“It’s starting to get to the point where this grass is beyond control in Antarctica,” says Kevin Hughes, an environmental scientist with the British Antarctic Survey.

International law forbids the introduction of new species to Antarctica. But the rules are fuzzier about what steps should be taken to deal with species that have become established in the wild. Nothing has been done to get rid of the grass intruder, Hughes says.

What impact the plant will have on native life isn’t yet known. But the same species has already overrun islands near — but not part of — Antarctica. On the island of South Georgia, the grass has replaced indigenous vegetation in some spots and stunts the growth of beetles that have trouble digesting the grass.

What’s bugging Antarctica

Plants aren’t the only potential invaders. Research stations have become beachheads for microbes, fungi, insects and worms. In 2005, construction vehicles brought by ship to a British outpost came with attached soil teeming with life. Produce imported to feed visitors can also carry infested dirt.

“About 12 percent of all fresh food items traveling to Antarctica are contaminated,” says Dana Bergstrom, a polar ecologist with the Australian Antarctic Division in Kingston. Bergstrom and colleagues reported that statistic last year in Biological Conservation after examining more than 11,250 fruits and vegetables shipped to nine research stations.

Contaminated soil is supposed to be destroyed when discovered, but a few foreign agents have slipped through the defenses.

Flies made themselves at home in the sewage system of an Australian research station and in a British station’s liquor store. Initial efforts to eradicate the insects failed at the Australian base. Their eggs endured, allowing the pests to spawn year after year. When reporting on the insects in 2005 in Polar Biology, Hughes and colleagues suggested that the bugs couldn’t survive the bitter cold outside, meaning they probably wouldn’t spread into the wild.

But another type of foreign fly with long legs has been sighted on King George Island. No one knows for sure how far Trichocera maculipennis has spread or how to get rid of it. Other interlopers now enjoying the fresh air include a worm and a species of midge that has multiplied in recent years.

With critters from abroad swooping in by land, by sea and by air, there’s good reason to put caution first, says Mahlon “Chuck” Kennicutt II, an oceanographer at Texas A&M University in College Station and president of the Scientific Committee on Antarctic Research. Antarctica, he says, offers a natural laboratory like no other on Earth. Its largely untouched environment helps scientists understand not only the rugged flora and fauna that can live in such habitats but also the planetwide effects of climate change.

“Antarctica is one of our last true wilderness areas,” says Kennicutt. “There are very few of those places left in the world. We’d like to keep them protected.”