Hakai Magazine

Coastal science and societies

Ice floes and coast, Antarctica
As the planet warms, the geophysical barriers that have long kept Antarctica safe from invaders are starting to erode. Photo by Colin Monteath/Hedgehog House/Minden Pictures

Kelp Rafts Are Bringing Invaders to Antarctica

Animals have long rafted around the planet, but the southern continent was considered too remote, too isolated, and too cold for that to be a problem—until now.

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by Brian Owens

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Antarctica is, for the most part, cut off from the rest of the planet by swirling ocean currents, raging winds, and frigid temperatures. The continent’s physical isolation has long been thought to have kept it well protected from invasions of nonnative species. But the discovery of living creatures on kelp rafts in Antarctic waters—including some known to be invasive in other cold regions—shows that the physical barriers are not insurmountable and invasions could become more common as the climate warms.

Though inhospitable to most life, Antarctica is not immune to introduced species. Most, such as the flightless midges that have infested Signy Island, have been inadvertently brought in by humans. And while rafting in on kelp had previously been identified as a way for nonnative species to arrive, it was considered unlikely given the breadth of the Southern Ocean and the weather and ocean current patterns that tend to push such rafts north.

Huw Griffiths, a marine biologist with the British Antarctic Survey, and his colleagues, however, recently collected more than a dozen kelp rafts from the Southern Ocean and the beaches of Antarctic islands. The rafts, which were made of kelp species that are not native to Antarctica, were transporting thousands of other species. Some, such as goose barnacles (Lepas australis), are not a threat because they only live in the open ocean. But others, having somehow survived the long and harrowing journey, could make a new home on Antarctica.

One species the scientists found, a tiny colonial animal known as a bryozoan, is particularly worrying. It is known to be a harmful invader in other cold water regions. If it made the jump from a raft to a native kelp, it would encrust the seaweed, cutting off its access to sunlight with potentially devastating consequences. “The local kelp is a major part of the ecosystem, and it may not have defenses against this bryozoan,” says Griffiths.

Even more worrying, he says, is where the bryozoan was found—on Deception Island, in the relatively warm water in the flooded caldera of an active volcano. “It’s one of the easiest places to get a foothold [in Antarctica] because it’s missing all the things that stop animals from getting established” such as the typical deep freeze seen on the mainland, says Griffiths. “From there, invaders would have a chance to adapt and spread.

“For so long we have believed Antarctica was isolated and cut off, but this shows that there are routes in.”

And new oceanographic models explain how: though still a rare occurrence, storms could occasionally push kelp rafts south. And with an estimated 70 million kelp rafts adrift in the Southern Ocean at any time, it’s perhaps not surprising that some have been found washed up on Antarctic beaches.

Karla Heidelberg, a biological oceanographer at the US National Science Foundation, says the risk of these kinds of natural invasions will only grow as the continent warms. Earlier this month, Antarctica twice shattered high temperature records. “We’re taking away the temperature defense, so there is a better chance that organisms can take hold,” she says.

While there are strict biocontrol rules in effect to protect the continent from human-aided invasions, there is little that can be done about natural kelp rafts. But Griffiths says it is important to monitor the rafts to determine which organisms are hitching a ride and which might be able to survive in Antarctica. And he wants to keep an especially close eye on Deception Island.

“It’s a testing ground for what climate change could do in the rest of Antarctica,” he says.