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 Ms. Bruning dove 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, Ms. 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.