Neodenticula seminae, a microscopic strand of photosynthesizing plankton, is common in much of the northern Pacific Ocean.

The plankton hadn't been seen in the northern Atlantic in some 800,000 years—until a survey in 1999 turned up a bunch in the Labrador Sea. Researchers speculate it traveled along with a pulse of warm Pacific water, part of the changing circulation patterns in the far north due to global warming.

Warming’s most obvious oceanic effect is the opening of the fabled Northwest Passage for the first time in recorded history. Which makes it more likely for N. seminae to have fellow travelers.

Pacific zooplankton—microscopic animals—have made the trip, and clams, oysters, snails and slugs may soon follow. These Pacific denizens could displace or disrupt their Atlantic cousins, potentially transforming the entire food web. Which is why a consortium of 17 marine institutes in 10 European countries is now monitoring the migrations, an effort known as Climate Change and European Marine Ecosystem Research.

Over the last decade, N. seminae has firmly established itself in the Labrador Sea, waters near Iceland and the Gulf of Saint Lawrence. You can’t call the plankton a fish out of water. But you can say that its waters are changing—and fast.

—David Biello