Alien species are invading Antarctica from as far away as the Arctic — and could fundamentally alter ecosystems in the world's last relatively untouched continent, an international team of scientists has reported.
The risks from these biological interlopers — seeds and plant material carried in on the shoes and clothing of well-meaning scientists, ecotourists and support staff — will increase as the icy content continues to thaw because of climate change, the scientists reported Monday in the journal Proceedings of the National Academy of Sciences.
People think of Antarctica as a pristine wilderness, but that is fast changing, said lead author Steven Chown of Stellenbosch University in South Africa. Over the last few decades, human activity there has increased dramatically. During the 2007-08 summer season, about 33,000 tourists and 7,000 scientists (including support personnel) made landfall there, bringing unintended ecological consequences, Chown said.
To get a handle on the scope of the problem, Chown and an international team of scientists surveyed nearly 5,700 tourists, scientists, ship's crews and support staff during the 2007-08 summer season. They also vacuumed clothes, bags and other travel gear of about 850 people, finding 2,686 stowaway seeds among the detritus that they identified by species or family using photographs from plant databases.
Chown said that from the analysis, he and his colleagues estimated that more than 70,000 seeds tagged along with the human visitors during that time window.
Each visitor brought an average of 9.5 seeds, the study said. The rates were much higher for scientists: About two-fifths of scientists at research stations brought seeds with them, double the rate for tourists. Scientists doing field work brought even more.
About half those seeds hailed from very cold climes such as the Arctic or the Alps, making them good candidates for surviving and thriving in the harsh polar environment.
"Many people have thought Antarctica is just an ice-covered place, there's no chance that things are going to establish there, but of course that's not true," Chown said. "One of the things that surprised us all was simply the scope of the numbers of seeds coming into the continent."
That could alter ecosystems that have remained undisturbed for perhaps a million years, potentially driving native plants extinct, said Peter Convey, a terrestrial ecologist with the British Antarctic Survey who was not involved in the study. Foreign invaders — in the U.S., think tumbleweed (originally from the Ukraine) or kudzu (from southern Japan and southeast China) — can spread like a bad rash.
"Invasive species that thrive and survive have a tendency to really change the ecosystem," said Mahlon Kennicutt, an oceanographer at Texas A&M University and president of the Scientific Committee on Antarctic Research, who was not involved in the study. "So there is concern that the natural population, particularly vegetation, could be affected."
Scientists pointed to the fates of nearby sub-Antarctic islands, where plants such as dandelions and mouse-eared chickweed have sprouted up like, well, weeds. "Some of them have more alien or non-native plant species than they have native plant species," Convey said.
It isn't really strange that seeds could have come from so many far-flung places, Chown said. Visitors to the Antarctic are typically very well-traveled. The scientists and tourists surveyed in the report had, as a group, previously visited every country in the world with the exception of French Guiana.
Convey said the study pointed to the need for travelers to be more mindful of what they bring to Antarctica's icy shores.
"You do feel some responsibility not to make a mess of it when you go as a scientist," Convey said. "You don't simply take dirty rucksacks and dirty boots and dirty outside clothing."
Although the study focused on invasive plants, animals could become a greater problem on the Antarctic islands as the climate warms, scientists said.
"If rodents ever got in, they'd be a real pest because rats have a habit of feeding on birds — and there's huge, vast bird colonies in Antarctica," Chown said. Even penguins might be at risk. "Penguins are more feisty than others, and rats don't tend to feed on penguins. But if they were desperate they'd have a go."