Invertebrates
Yeti Crab
Kiwa hirsuta · also called yeti crab
The yeti crab lives in one of the harshest places on the planet — the scalding, mineral-laden water around deep-sea hydrothermal vents — and survives by farming bacteria on the dense blond bristles covering its own claws, waving them in the current to help the crop grow.
Overview
Yeti crabs live around deep-sea hydrothermal vents of the southern Pacific, at depths near 2,200 metres. About 15 cm across, pale-bodied with claws and legs covered in long silky bristles, they eat mostly bacteria they cultivate on those bristles.
Farming its own food
The bristles host thick colonies of chemosynthetic bacteria that feed on vent chemicals, which the crab then harvests with comb-like mouthparts. It waves its claws in the vent flow to keep the crop supplied.
Only known since 2005
First found in 2005, it was distinctive enough to warrant an entirely new family of animals.
Status
The yeti crab is Not Evaluated, known only from a few naturally patchy vent sites now of interest for deep-sea mining.
Yeti Crab: common questions
Why does the yeti crab have hairy claws?
The dense covering of long, silky bristles on the yeti crab's claws and legs is not fur and serves a very specific purpose, acting as a large surface area on which the crab cultivates thick colonies of bacteria. These bacteria are chemosynthetic, meaning they produce energy from chemicals dissolved in the water flowing out of hydrothermal vents rather than from sunlight, and the yeti crab effectively farms them, growing its food supply directly on its own body before harvesting and eating it. The bristles maximise the space available for this bacterial garden, making them central to how the crab feeds itself in an environment with almost no other food.
How was the yeti crab discovered?
It was first encountered in 2005 by researchers using a deep-diving submersible to explore hydrothermal vent fields along the Pacific-Antarctic Ridge, a volcanic ridge on the seafloor south of Easter Island, at a depth of roughly 2,200 metres. The animal was so unusual, particularly its dense, hair-like bristles and its association with vent chemistry, that scientists concluded it represented not only a previously unknown species but an entirely new family of crustaceans, which was named Kiwaidae after Kiwa, a figure associated with the sea in Polynesian mythology.
Why does the yeti crab wave its claws around?
Observations of yeti crabs near vents have shown them rhythmically waving their bristled claws back and forth through the water streaming out of a vent, and the leading explanation is that this movement helps the bacterial colonies living on the bristles by continuously bathing them in a fresh supply of the dissolved chemicals, such as sulphides and methane, and oxygen that the bacteria need to grow. In effect, the crab is tending its crop, using its own body movements to improve the growing conditions for the microbes it depends on for food, much as a farmer might irrigate or aerate a field.
How does the yeti crab survive next to near-boiling water?
Hydrothermal vents release water that can exceed 300 degrees Celsius right at the vent opening, far too hot for any animal, but this superheated water mixes rapidly with the surrounding near-freezing deep-sea water, creating a narrow zone of intermediate temperatures nearby. The yeti crab must position itself carefully within this zone, close enough to the vent that its bacterial crop receives an adequate flow of the chemicals it needs, but far enough away that the crab is not cooked or poisoned by the most extreme conditions, effectively living its whole life balanced along a steep gradient of temperature and chemistry.