On glaciers, a cosy home for moss

Life has a habit of turning up in the most unlikely of places. Geysers, desert cliffs, even heaps of dung are environments that at least a few creatures call home. Now balls of moss on glaciers are joining this strange list. The clumps, known as glacier mice, have been found to contain miniature ecosystems. And even in freezing temperatures, scientists found, the inhabitants manage to thrive.In high winds glacier mice, which form when clumps of dust and organic debris develop a layer of moss over time, hop across vast sheets of ice.

Because glaciers are in constant, if slow, motion and are frequently blasted by strong winds, these clumps roll around a bit like tumbleweed, or dust bunnies, and the moss ends up growing on all sides.

After years of growth, the clumps look like mouse-size green balls of vegetal fluff, thus their name. Yet in spite of all the information that has been collected about how glacier mice form and get around, their innards remained a mystery.

Keen to better understand them, Steve Coulson, an Arctic biologist at the University Center in Svalbard, Norway, decided to turn his attention toward the guts of the bizarre formations.

He and a colleague, Nicholas Midgley, at Nottingham Trent University in England, knew that the mice often accumulated a lot of dust in their travels and could potentially function like roving sponges, soaking up water wherever they went. They speculated that the protective moss layer would cut the wind and keep temperatures slightly warmer than those on the ice and, combined with a constant water supply, might lead animals to seek out glacier mice as sanctuaries.

At Falljokull glacier

To explore these possibilities, Midgley went to the Falljokull glacier in southeastern Iceland. He collected 10 glacier mice for closer examination and stuck probes in five others that would measure their internal temperatures over a two-week period. Back in the lab, Coulson then picked apart the collected specimens to look for animals and stuck the remains inside a drying oven so that water content could be calculated.

They report the discovery of a new ecosystem in a paper in the June issue of Polar Biology. Inside the mice, the researchers found Collembola (six-legged insectlike creatures commonly known as springtails), tardigrades (tiny eight-legged moisture-loving creatures that are often called water bears) and simple nematode worms. And contrary to what the team expected, these animals were not just getting by inside the glacier mice; with up to 73 springtails, 200 tardigrades and 1,000 nematodes being found in just a single mouse, they were thriving.

“I had expected to find some animals, but not so many,” Coulson said. What he found particularly surprising was that the springtails were of many different age groups. “This hints that they might be breeding inside the mice,” he said.

The animals’ success made sense when Coulson took a look at data from the probes and the drying oven. Compared with the temperature of the glacier, which was 0 degrees Celsius, or 32 degrees Fahrenheit, the mouse temperatures ranged from 2 to 10 degrees Celsius (about 36 to 50 degrees Fahrenheit). In addition to the warmth, each of the collected mice carried about a gram of water – just a few drops, but more than enough to keep the tiny environment perpetually moist.

Peter Convey, a polar ecologist at the British Antarctic Survey, said the individual mice exist for only a few years before falling apart. But, he said, “with the Collembola potentially breeding inside of them and the ability for these animals to move from one mouse to another when wind causes them to collect in a small area, it would seem that the glacier mouse environment on the whole is functioning as a form of permanent ecosystem.”

New York Times News Service