What's white and blind and hairy all over? A yeti, of course! Or, in this case, a yeti crab — a marine creature that lives near the thermal vents in the ocean floor where hot water gushes into the sea.
There are three known species of yeti crabs, and now, in a new paper, scientists have described the characteristics of one of these species — Kiwa tyleri — for the first time. K. tyleri is the only species of yeti crab known to reside in the Southern Ocean, off Antarctica.
Researchers first photographed this deep-sea animal in 2010 using a remotely operated submersible vehicle (ROV). But the ROV did more than snap a few pictures of the furry crabs (some of which you can see here); it also vacuumed up a few specimens from about 8,500 feet (2,600 meters) beneath the Southern Ocean's icy surface, for further study. [In Images: The Amazing World of Antarctic Yeti Crabs]
Since then, researchers have studied the specimens using genetic sequencing and computed tomography (CT) scanning. Their description of the somewhat strange morphology of the yeti crab is published today (June 24) in the journal PLOS ONE.
Many of the yeti crab's distinctive features — like its stark white coloring and its "hairy" body — are the creature's adaptations to its habitat, the researchers said. K. tyleri dwells in a "thermal envelope" of just a few square meters, where the water is just the right temperature, said Sven Thatje, lead author of the report and associate professor of marine evolutionary ecology at the University of Southampton in England.
The crab's tiny habitat in the East Scotia Ridge (located in the Atlantic section of the Southern Ocean, between Antarctica and South America) contains "black smokers," which are chimneylike vents that spew dark water that can reach temperatures of about 720 degrees Fahrenheit (380 degrees Celsius). The yeti crabs live right on top of these scorching vents.
"They're literally, in places, heaped up upon each other," Alex Rogers, a professor of zoology at Oxford University who led the expedition to the East Scotia Ridge, told Live Science in 2012. Photographs taken by Rogers' team show 600 crabs per square meter.
The reason for the crabs' tiny living quarters is simple: The water just outside their cozy home is very cold, Thatje told Live Science in an email. Water temperatures at that depth of the Southern Ocean typically fluctuate between about 30 and 33 F (minus 1.3 to 0.5 C).
"Crabs and lobsters are very rare in Antarctic/Southern Ocean waters because of the unusually low seawater temperatures," Thatje said. "A physiological limit to maintaining activities required for survival (ventilation, molting, mating) appears to exist at around 0.5 degrees C [32.9 degrees F]."
But some crabs do brave the icy waters away from the vents. Female yeti crabs leave the vents to brood their eggs, which researchers believe need cooler water to develop. The eggs would also be unlikely to survive so close to the hydrothermal vents' sulfur-rich emissions, Thatje said. But these mama yeti crabs have a thankless job: Once they are done brooding, they usually die, Thatje said.
"Females that move off-site do not feed; in fact, they starve," said Thatje, who hypothesizes that once the females leave the vents, they aren't strong enough to fight their way back into the crustacean melee.
Yeti crabs survive by growing their own food, in a sense. The distinctive "hair" on their bodies that gives them their name is scientifically known as setae, and serves as a "garden" where the yeti crabs' favorite food — bacteria — grow.
Unlike Kiwa puravida —the yeti crab found near hydrothermal vents off the coast of Costa Rica that has setae only on its appendages —the Antarctic yeti crab also has setae along the underside of its body. The appearance of this "chest hair" led scientists to nickname Kiwa tyleri the "Hoff crab" after "Baywatch" actor David Hasselhoff, who (as you may recall) has a hairy chest. [From Blobfish to 'Adorable Octopus': 9 Animals with Perfect Names]
This difference in setae between the Antarctic yeti craband its two closest relatives, Kiwa puravida and K. hirsute (which inhabits the waters south of Easter Island, along the Pacific-Antarctic Ridge), is "remarkable," Thatje said. It's likely that the Hoff crabs' hairy chests are an adaptation. Their luxurious setae allow the Hoff crab to not only grow its own bacteria, but also swipe up bacteria that grow on the vent chimneys.
Thatje noted another adaptation that is particular to Kiwa tyleri:The crab has "spikes" on the end of its legs that allow it to climb steep surfaces. "This is a significant advance in its evolution, and differentiates it from the other known yeti crabs, which clearly do not possess the ability to climb vent chimneys," he said.
Although Thatje and his colleagues have shed light on some of the mysteries surrounding the elusive yeti crab, many questions remain. Further research is needed to understand how these heat-loving crabs came to colonize two vent systems that are separated by miles of frigid water, and how the yeti crab larvae make their way from the frigid depths of the Southern Sea to the cozy chimneys they eventually call home.