Antarctica is not invulnerable to an influx of new species

Life in Antarctica is vastly different from anywhere else on Earth. The species that inhabit the southernmost continent and its surrounding waters have evolved in apparent isolation, with almost no ecological interaction with non-Antarctic species for at least the past 18 000 years. Researchers have attributed that separation to the Southern Ocean’s powerful winds and currents, thought to prevent organisms adrift at sea from ever reaching Antarctic shores.

Ceridwen Fraser , Adele Morrison (both at the Australian National University), and their colleagues now show that interpretation to be incorrect: The drifting of plants and animals from lower latitudes to the Antarctic is not just possible but frequent. The inhospitable climate, however, means that the newcomers die instead of taking up residence.

It all started in early 2017, when two pieces of southern bull kelp turned up on King George Island, right next to the tip of the slender Antarctic Peninsula. The kelp grows throughout much of the Southern Hemisphere—although not, so far, in Antarctica—and its toughness and buoyancy enable it not only to endure long journeys at sea but to carry shellfish and other organisms across oceans as well.

Fraser, an expert on southern bull kelp, analyzed the DNA of the newfound specimens to determine their geographic origins. One, she found, had come from the Atlantic island of South Georgia, the other from the Kerguelen Islands in the Indian Ocean.

But how did they get to Antarctica? For that, Fraser turned to Morrison, an experienced ocean modeler, who eventually found the answer: Stokes drift, a nonlinear phenomenon of wave motion, causes surface particles to drift at velocities slightly different from those of the underlying currents, especially during storms. In a computer simulation that included the effects of Stokes drift, 8000 out of 4 million floating objects released from South Georgia eventually reached Antarctica. Without Stokes drift, none of them did.

As the climate changes, the researchers conclude, the unique plants and animals of Antarctica face a double threat. They’ll have to contend with not only the rising temperatures themselves but also increased competition from nonnative species that are better adapted to warmer conditions. (C. I. Fraser et al., Nat. Clim. Change 8, 704, 2018 ; photo by Ceridwen Fraser.)