Given its geographic isolation and bone-chilling temperatures, Antarctica has long held up a “no soliciting” sign when it comes to invasive species. But now the first successful marine invaders have breached the White Continent’s door.
Scientists found a colony of mussels, most likely transported from Patagonia via ship, near the largest of the South Shetland Islands some 75 miles north of the Antarctic Peninsula. This discovery, published last month in Scientific Reports, is a harbinger of future invasions, the researchers suggest, particularly as climate change afflicts the Southern Ocean and ship traffic in the region increases.
Paulina Bruning, a marine biologist at Laval University in Québec City, never set out to find mussels in Antarctica. When Bruning dived in the 36-degree water of Fildes Bay on King George Island, she was focused on collecting native coral and sea sponges.
But back in the laboratory, Bruning spotted several dozen juvenile mussels clinging to one of her specimens, an orange sponge. That was unexpected — mussels aren’t native to Antarctica. In fact, there’s never been any evidence of young mussels surviving in such cold water.
The bivalves, just a few months old, were barely larger than a pencil tip. “They’re like black dots,” said Jean-Charles Leclerc, a marine ecologist at Chile’s Catholic University of the Most Holy Conception, and a member of the research team. “You need to look closely.”
Using DNA sequencing, the scientists concluded that the animals were probably Patagonian blue mussels. They must have traveled about 500 miles from warmer waters near the southern tip of South America. But the bivalves probably didn’t drift there, because circulating ocean currents effectively barricade Antarctica. “Natural transport is really unlikely,” Leclerc said.
But ships, particularly research and tourist vessels, frequently travel between South America and the South Shetland Islands. From 2017 to 2019, more than 200 ship stopovers occurred at Fildes Bay. This bay, close to numerous research stations and penguin colonies on King George Island, is “the door of Antarctica,” said Leyla Cárdenas, a geneticist at the Center for Dynamic Research of High Latitude Marine Ecosystems in Chile, who led the new research.
And with ships come stowaways — adult mussels often cling to vessel hulls. “People have been moving sea creatures around the world for probably as long as we’ve been moving around the oceans, particularly things that like to be stuck on ships,” said Arlie McCarthy, a zoologist at the University of Cambridge, not involved in the research.
The mussels in Fildes Bay probably attached themselves to a ship in Patagonia and hitched a ride through the Drake Passage, Cárdenas and her colleagues proposed. The animals likely released their sperm and eggs in Antarctica, where fertilization occurred. The orange sponge that Bruning found cocooned the mussels as they grew into juveniles, the team suggested.
It makes a lot of sense that mussels would be Antarctica’s first marine invaders, said Kevin Hughes, an environmental researcher at the British Antarctic Survey in Cambridge, not involved in the research. They’re plentiful in Chilean and Patagonian waters, and they’re extremely good at attaching themselves to ships, he said. At a 2018 workshop that Hughes attended, researchers tabulated the nonnative species most likely to invade the Antarctic Peninsula region within the next decade. “Right at the very top of our list was mussels,” Hughes said.
For now, Antarctic conditions are still extreme enough to thwart all but the hardiest invaders. But as ship traffic increases and the Southern Ocean warms, invasions will probably become more frequent, Leclerc said. “Species might find suitable conditions in the future.”
A few months ago, Bruning and other researchers returned to Fildes Bay. However, there was no sign of the mussels. It seems that they didn’t make it through the brutal Antarctic winter, four months with water temperatures below 30 degrees. But the team isn’t giving up on the search, Cárdenas said. “We’re planning to go next year.”