• These shrimp have no eyes. Image from Luis Espinasa et al. (New Scientist)Source: New Scientist
Tiny crustaceans from deep ice caves don't have eyes, but they can still somehow sense light, and survive being frozen solid.
Brian Owens

New Scientist
30 Mar 2016 - 11:46 AM  UPDATED 30 Mar 2016 - 11:46 AM

Species: Stygobromus allegheniensis

Habitat: Caves throughout the north-eastern US

Deep in the ice caves of the Shawangunk Ridge in New York state lives a tiny crustacean with unique abilities.

Despite being eyeless, it can still detect some wavelengths of visible light. And it has no problem with being frozen solid during the frigid winters.

Luis Espinasa, a cave biologist at nearby Marist College in Poughkeepsie, New York, first came across the 2-centimetre-long shrimp while hiking with his young son Jordi shortly after moving to the area. “I was looking for critters in the caves, like I always do, when he called out ‘Hey dad, look at these!” recalls Espinasa.

Years later, Jordi decided to study the creatures further for a high-school science class. He wanted to know how the little shrimps survived in the icy home over the winter.

Although there are examples of animals that can survive being frozen solid, few, if any, have been found in caves. “Cave dwellers are typically not adapted to freezing,” says Espinasa.

They don’t usually need to be: most caves, such as the limestone caves where S. allegheniensis is more commonly found, maintain a fairly steady temperature throughout the year.

Life in the freezer

The ice caves, however, are different. They are tectonic, having been formed by faults and cracks in the rock. Snow and cold air enter the caves through openings at the top and are then unable to escape, creating a refrigerated environment in which some of the walls and floors become covered in solid ice.

Experiments in both the field and lab showed that the shrimp were able to survive and return to swimming normally after being frozen in solid blocks of ice for several hours (see video below).

Espinasa believes they can probably survive much longer in natural conditions, given that they would have weeks to adjust their physiology in preparation for winter.

It’s still not clear how the creature deals with being frozen, but that will be one of the next research steps for the students in Espinasa’s lab.

Animals generally survive a deep freeze by filling their body with substances – such as glycerol, a variety of sugars or amino acids – that lower the freezing point of the water inside them, and prevent ice crystals from forming and destroying their cells.

“My guess is it is one of the above,” says Espinasa. “I don’t expect we’ll find new physiological chemicals, but you never know.”

His team also found in tests that the eyeless shrimp could distinguish between light and dark, with the creatures being drawn to the dark – a feature known as scotophilia.

Espinasa doesn’t know what they use instead of eyes, but early results suggest that the light-detecting structures may be on their heads.

Journal reference: Subterranean Biology, DOI: 10.3897/subtbiol.15.4733

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