You might think glaciers would be hostile to life. But small water-filled holes at the surfaces of glaciers called cryoconite holes contain diverse collections of organisms. Like individual cities in a continent of ice, each hole contains its own distinct population of creatures.
Some scientists believe glaciers should be considered a separate biome given the unique ecosystems that thrive there.
While the bacteria that live in cryoconite holes have been studied extensively, little is known about the invertebrates that feed on them and on algae found in the holes—only 26 papers have been published on these invertebrates in the past 100 years. Polar biologist Krzysztof Zawierucha from the University of Poznan in Poland and other researchers recently attempted to catalog these invertebrates in a review paper published in the Journal of Zoology.
Cryoconite holes, are created by cryoconite—windblown dust containing rock particles and soot—which darkens the surfaces of glaciers and accelerates melting. Cryoconite holes can form long-lasting habitats given that they are relatively unaffected by rapid environmental changes. These holes can be covered over by ice, or open to the elements. For a brief explanation of what cryoconite is and how cryoconite holes are created, watch this video:
Only 25 species of cryophilic invertebrates have so far been catalogued and studied, few of them endemic to cryoconite holes. These include insects and two phyla of worms (the ringed worms also known as annelids, and roundworms also known as nematodes), as well as the microscopic rotifers, and the less well known waterbears, whose technical name is tardigrades.
The species makeup of the cryoconite holes differs slightly in the Arctic, Antarctic, Patagonian, Alpine and Himalayan glaciers where they have been studied. Some of these hole-dwelling invertebrates have geographically restricted ranges, existing only on glaciers in the Alps or Himalayas. The authors suspect there are many more species living in these remote ice holes waiting to be discovered.
The invertebrates are varied in coloration; some are black, others white, and still others are colorless; Zawierucha and his coauthors cite other studies indicating that the coloration may have adaptive value in these environments where ultraviolet radiation is strong. They have different mechanisms for surviving the very low temperatures and the threat of desiccation: some produce very hardy eggs, while others can enter a state of anabiosis—a sort of suspended animation—until conditions improve.
Cryophilic ecosystems are threatened due to the melting of glaciers caused by climate change and pollution. But cryophilic animals may accelerate the melting of glaciers themselves, particularly those that are black in coloration. Because so little research has been conducted on them, it is possible that some species of cryophilic invertebrate will become extinct before it is catalogued by scientists. If you happen to stumble upon a cryoconite hole on a glacier, treat it with respect. It likely contains an entire world of busy organisms.
For a story on plant spores that live on glacier surfaces, look here.