by Whit Gibbons

July 9, 2017

The first water bear I ever saw came lumbering through the water, pushing over a pile of floating debris. It grabbed another piece of rubble with a front leg and moved it aside like it was a sofa cushion.

I knew it was in control of the scene when it came face to face with a paramecium, which used all of its cilia to get out of the way. I was looking through a microscope in biology class observing one of nature’s most remarkable creatures. At the time, I did not know how special a water bear, or to use its proper name – tardigrade, was. Scientific research years later has revealed how extraordinary tardigrades are.

“Tardigrades belong to the most radiation tolerant animals on Earth,” says a scientific paper by Jonsson K. Ingemar (Kristianstad University, Sweden) and colleagues from the University of Copenhagen, Denmark. They are distinctive in being the only animals known to have “survived the combined exposure to cosmic radiation, UV radiation and vacuum under real space conditions.”

These statements are based in part on the survival of tardigrades placed on the outside of an unpiloted Russian spacecraft. In the experiment, conducted in collaboration with NASA, more than two-thirds of the tardigrades survived the trek, enduring environmental conditions far harsher than any on Earth.

Tardigrades are chubby microscopic organisms, the largest ones approaching the size of a grain of rice. They have eight legs with disk-like claws at the end and a cute nose resembling a piglet’s snout. If these charming little denizens of terrestrial, freshwater and marine habitats worldwide were a familiar mammal like real bears, the toy industry would be awash in stuffed water bears. Every child (and some adults) would want one.

Science writer William Herkewitz reported in Popular Mechanics on the near-invulnerable nature of these fascinating animals. He noted that tardigrades have survived heat of more than 300 degrees Fahrenheit and cold as low as -458°F.

As another measure of the resilience of these remarkable organisms, Fumihisa Ono (Okayama University of Science, Japan) and colleagues reported tardigrades surviving incredibly high pressures – more than a million pounds per square inch. The investigators stated that it “was really surprising that living organisms can survive after exposure to such a high pressure.”

Tardigrades are versatile and ubiquitous as seen by their presence on all continents and habitats from arid deserts to frozen tundra, from mountain tops to deepest oceans. No other animals have been found to tolerate the extremes a tardigrade can endure.

What is the scientific explanation for such incomparable endurance? An ability to dehydrate so that only a small percentage of their body retains water has been proposed as one survival mechanism. Another is that they can lower their metabolism to the point that it is barely measurable.

When in such a physiological state, a tardigrade can go for years, perhaps decades, without its basic food of algae or bacteria and without any water. Why that would also allow it to survive phenomenally high atmospheric pressure in a laboratory, a vacuum in outer space or high levels of radiation is not clear.

Hundreds of different species of tardigrades are known to exist, and only a few of them have been examined thoroughly enough to know what other special capabilities they have. The potential for research on tardigrade behavior is intriguing. Water bears have much to tell us about life and the myriad ways it can be lived. They may even show us how to survive an interplanetary voyage.

Space exploration is something we should continue to support in our ongoing efforts to unveil the mysteries of outer space. But let us not forget that intrigue and mystery are also to be found here on our home planet. Information lies beneath our feet, waiting to be revealed through research on the millions of species like tardigrades that we know too little about.

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