A new synthesis finds that glaciers divide into distinct habitats, including melt pools, rocky debris, and moss ball "glacier mice," with each zone hosting its own characteristic animals, nearly half of which exist nowhere else.
A glacier looks like a white blank. That is the picture most people carry: a smooth, featureless field of ice, identical from edge to edge. A new synthesis of glacier ecology finds that picture wrong. Glaciers are subdivided into distinct habitat zones, and each one hosts its own characteristic community of animals. The ice is not uniform. It is an archipelago.
The synthesis, published today in the Proceedings of the National Academy of Sciences USA, pulled together scattered research on glacier-dwelling animals and mapped them to the parts of the ice they actually live on. The work, by a team that includes Andrea Simoncini, a Ph.D. student in environmental sciences at the University of Milan, in Italy, identified more than 150 different animal species living on glaciers. The headline number is a roster. The more interesting finding is the geography.
The best doorway into that map is a creature readers may already know: the tardigrade, the microscopic eight-legged animal sometimes called the water bear. Tardigrades show up reliably in cryoconite holes, the small, dark-bottomed pools of meltwater that form when dust and debris absorb heat on the ice surface. Rotifers, another group of microscopic animals, share the same habitat. Cryoconite holes are, in effect, the glacier's ponds, and they have a pond-like community.
Move off the pools and onto the surface debris, the loose rock and grit scattered across the ice, and the residents change. Nematodes, tiny roundworms, are common here. So are springtails, six-legged relatives of insects that look like specks of dust until you look closely. The shift is not subtle: different habitats on the same glacier support different animal communities, a non-random pattern that contradicts the white-field picture.
Then there are the glacier mice: round, tumbling balls of moss that sit on the ice surface and roll as the wind pushes them. Researchers have found them harboring their own invertebrate communities, including tardigrades and rotifers, and the inventory of which species live where inside a moss ball is still being filled in. Glacier mice are a habitat as well as a curiosity.
The more dramatic residents are less familiar. In Patagonia, a stonefly called Andiperla willinki, a small insect whose closest relatives live in cold, clear streams, has been found nowhere except the glaciers of Chile. It is the kind of animal that exists only because the ice exists. The synthesis reports that nearly half of the more than 150 species identified have been recorded only at glacial sites. The same animal, the same ice, the same narrow geography.
The research team, including Simoncini, was not simply compiling a list of oddities. They were looking for structure. What they found is that glacier habitats, including cryoconite holes, supraglacial debris, moss-ball surfaces, and the ice itself, partition their animal communities the way forests partition theirs into canopy, understory, and floor. The ice has a geography.
That geography is also a vulnerability. A cryoconite hole that vanishes in a warming summer takes its tardigrades and rotifers with it. A stonefly endemic to a Chilean glacier has no other glacier to move to. The synthesis does not need to make the climate case in capital letters; the pattern supplies the stakes. When a glacier retreats, what disappears is not just ice. It is a set of named, characteristic neighborhoods, each with its own residents, most of which exist nowhere else.
The study, reported by Meghan Bartels for Scientific American, is also a map of what researchers have not yet looked at carefully enough. Sampling on glaciers is sparse, biased toward a few accessible sites, and the taxonomy of small glacier invertebrates is far from settled. The synthesis is less a final inventory than a first pass at a system that has been hiding in plain sight, on ice that most people have been told is empty.