These unassuming holes are havens for invertebrate life (Image: Sara Penrhyn Jones)

Our planet’s ice is anything but barren. Upside-down forests cling to the underbelly of polar sea ice, while icebergs are ecological hotspots boosting life in the water around them.

Now, it turns out that glaciers support an unlikely variety of creatures, too, in curious habitats made possible by wind, dust and the sun’s heat.

The surface of a glacier is riddled with holes. Some are needle-thin, others a few metres across, but inside all a secret ecosystem is thriving.


A team of researchers led by Krzysztof Zawierucha, from the Adam Mickiewicz University in Poznań, Poland, has made the first worldwide survey of invertebrates living in these “cryoconite holes”.

They found 25 species, many of which are unique to this habitat. The Arctic is home to 16 of them, with the remainder distributed across Antarctica, the Himalayas, the Americas and the Alps.

The holes occur when windblown dust – cryoconite – settles on the glacier surface. Being darker than the ice, the dust absorbs more heat, resulting in a pool of melted water with a layer of silt at the bottom. The pools are typically around 15 to 20 centimetres deep, and can grow up to several metres in diameter.

Perfect refuge

Like a desert oasis, these sheltered reservoirs provide the perfect refuge for a host of organisms to flourish. Some of these are hardy creatures that arrive on the wind; others seem to be specialised to life in these holes.

“It’s very hard for anything to live within, underneath or on the surface of the glacier, so cryoconite holes are very much hubs of activity,” says Karen Cameron, from the Geological Survey of Denmark and Greenland.

The first organisms to colonise the holes are probably windblown arrivals: filamentous cyanobacteria. They are effectively ecosystem engineers, bundling together the dust, soot and organic matter, says Arwyn Edwards of Aberystwyth University, UK. This creates niches that pave the way for fungi, algae and other bacteria, which feed on organic matter. Then along come the top predators, including insect larvae, segmented worms, copepods and microscopic creatures called tardigrades – commonly known as water bears.

“In Arctic regions the big predator is the polar bear, but in cryoconite holes it is the water bear, which feeds on bacteria and algae. They are the toughest organisms on Earth,” says Zawierucha. These organisms survive the long winter by drastically slowing their metabolism and because they probably have antifreeze proteins, which makes them of interest to the pharmaceutical industry (see box below).

Stowaways from afar

They probably first arrived at the glaciers as stowaways on windblown dust, which may come from nearby mountains or tundra, or even from faraway regions such as the Sahara desert, says Cameron.

The holes can also harbour dormant seeds flown in from far away. Last year, Ronald Lewis-Smith at the Centre for Antarctic Plant Ecology and Diversity in Moffat, UK, managed to grow a fern from spores found in cryoconite holes in Antarctica.

Many of the species endemic to cryoconite holes are black, a finding that surprised Zawierucha. The production of dark pigments probably protects them from high levels of ultraviolet radiation, he says. But it may also help make their environment more habitable.

“The organisms that live in cryoconite strongly control the albedo, or reflectivity, of the holes by attracting more sunlight and, therefore, heating up their world,” says Joseph Cook of the University of Derby, UK.

In fact, these organisms are heating up their microhabitats so efficiently that they might be speeding up the melting of the glacier itself.

“This is a significant contributor to glacial surface melt, both on valley glaciers and the Greenland ice sheet,” says Edwards, who calls it “a biological preconditioning of a glacier to its death”.

“It’s a positive feedback mechanism,” says Cameron. “More cryoconite holes increases glacier melt that, in turn, increases the area of snow-free regions, a prerequisite for cryoconite holes. And in a hundred years’ time you’ll probably get more cryoconite holes in glaciers worldwide, and this could contribute to sea level rise.”

What will happen to the invertebrate communities living in these holes as their habitat warms? No one knows for sure. Edwards thinks the species might establish themselves in nearby habitats, such as coastal seas.

Journal reference: Journal of Zoology, DOI: 10.1111/jzo.12195

Secrets of glacial life Harnessing the tricks which hardy creatures use to survive in cryoconite holes on glaciers could help us make better pharmaceutical products, and give clues to how some common pathogens affect us. “We can learn a lot from these tiny animals,” says Krzysztof Zawierucha of the Adam Mickiewicz University in Poznań, Poland. For example, he says, the antifreeze proteins they use to survive cold winters may be added to drugs or vaccines to prevent them degrading in cold environments. Organisms such as tiny eight-legged tardigrades use special molecules that buffer their cells from osmotic pressures associated with freezing and thawing. These can be used to protect drugs and vaccines from similar freeze-thaw cycles. Some pathogens which lurk in our bodies, such as bacteria that cause tuberculosis, have something important in common with the bacteria in cryoconite holes, namely mechanisms that make them go dormant and later revive, says Zawierucha. One of these is a gene family called resuscitation promoting factor (Rpf), which serves as an “alarm clock” to wake dormant cells. This makes Rpf a possible avenue to new vaccines, drugs and diagnostic tests, and research is already under way in this area.