William von Herff writes:

In the Fram Strait off Greenland’s west coast, Véronique Merten encountered the foot soldiers of an invasion.

Merten was studying the region’s biodiversity using environmental DNA, a method that allows scientists to figure out which species are living nearby by sampling the tiny pieces of genetic material they shed, such as scales, skin, and feces. And here, in a stretch of the Arctic Ocean 400 kilometers north of where they’d ever been seen before: capelin.

And they were everywhere.

The small baitfish found in the northern Atlantic and Pacific Oceans is an ardent colonizer. Whenever the ocean conditions change, capelin can easily expand their range, says Merten, a marine ecologist at the GEOMAR Helmholtz Centre for Ocean Research Kiel, in Germany.

It is difficult to estimate an animal’s abundance based solely on the amount of its DNA in the water. Yet in Merten’s samples, capelin was the species most frequently encountered—far more than typical Arctic fish such as Greenland halibut and Arctic skate. To Merten, the evidence of so many capelin so far north is a bold sign of a worrying Arctic phenomenon: Atlantification.

The Arctic Ocean is warming quickly—the Fram Strait is nearly 2 degrees Celsius warmer than it was in 1900. But Atlantification is about more than rising temperatures: It’s a process that is reshaping the physical and chemical conditions of the Arctic Ocean. [Continue reading…]