Story by Shannon Wianecki
It might sound like a fairy tale, but it’s fact: Haleakala National Park is home to a troupe of tiny bears. But don’t bother searching for these wee creatures. Tardigrades, better known as water bears, are miniscule, ranging from 50 to 1,200 microns. Which means a couple of water bears could fit into the period ending this sentence.
Water bears are so named for their appearance and form of locomotion. Like microscopic grizzlies, they pad along on eight stumpy legs, brandishing claws and short snouts. Another name — moss piglet — refers to the animal’s most common habitat. Tardigrades are aquatic, but to creatures of their size, suitable swimming holes include the moisture clinging to mosses, or the capillary water between grains of sand. They are found all over the globe: in the arctic, desert, deep sea, and — most of all — in Hawai‘i.
Tardigrades living in Haleakala’s extreme conditions
“It turns out that the Hawaiian Islands, and Haleakala in particular, [are] the single richest place on earth for tardigrades,” says biologist Sam Gon III. He coauthored a paper on the subject after surveying Maui’s tallest mountain in 1985. He and his colleagues collected thirty-one tardigrade species in ten genera and four families in less than fifty square miles. Surprisingly, they found the highest numbers of tardigrades in Haleakala’s most extreme environments. Rather than basking in the waters of Waikane Spring, for example, the hardy animals proliferated at the frigid, wind-blasted summit. This capacity to thrive in hostile climates makes water bears among Earth’s most fascinating life forms.
When their wet habitats dry up, water bears undergo cryptobiosis — a state of suspended animation mimicking death. Their appendages retract; they lose 99 percent of their moisture and curl up into an impenetrable ball. Persisting in this state for months or years, they are virtually indestructible — immune to intense heat and cold, desiccation, crushing pressure, and caustic chemicals. Their very existence stretches the definition of “living.”
In 2007, water bears joined astronauts in space to see how they handled cosmic rays. Exposed for ten days to the vacuum of space, without oxygen, water, or heat, and zapped by intense solar radiation, water bears became the first animals to survive in space. Back on Earth, the mini-cosmonauts continued to breed successfully. Investigating the molecular makeup of these amazing creatures may show humans how to survive future space explorations.