An international team of scientists recently announced the discovery of a new species of blind deep-sea crab whose legs are covered with long, pale yellow hairs. This crab was first observed in March 2005 by marine biologists using the research submarine Alvin to explore hydrothermal vents along the Pacific-Antarctic ridge, south of Easter Island. Because of its hairy legs, this animal was nicknamed the “Yeti crab,” after the fabled Yeti, the abominable snowman of the Himalayas.

The Yeti crab was discovered during the Easter Microplate expedition to the southeast Pacific, led by MBARI scientist Bob Vrijenhoek. The primary goal of this expedition was to learn how bottom-dwelling animals from one deep-sea hydrothermal vent are able to colonize other hydrothermal vents hundreds or thousands of miles away. Vrijenhoek and his team were addressing this question by comparing the DNA of animals at hydrothermal vents in different parts of the Pacific Ocean.

During one Alvin dive, marine biologist Michel Segonzac, from Institut français de recherche pour l’exploitation de la mer (IFREMER) in France, noticed an unusually large (15-cm-long) crab with hairy arms lurking on the seafloor. Segonzac asked the Alvin pilots to collect this crab and bring it back to the surface.

The researchers saw more of these unusual crabs during subsequent Alvin dives. Most of the crabs were living at depths of about 2,200 meters (7,200 feet) on recent lava flows and areas where warm water was seeping out of the sea floor. According MBARI biologist Joe Jones, “Many of the crabs were hiding underneath or behind rocks—all we could see were the tips of their arms sticking out.”

After returning to shore, researchers Segonzac and Jones worked with Enrique Macpherson from the Consejo Superior de Investigaciones Científicas (CSIC) in Spain to identify the crab they had collected. They found that the crab was not only a new species (which they named Kiwa hirsuta), but an entirely new family (Kiwaidae). The Yeti crab is a distant relative to the hermit crabs commonly seen lurking in tide pools.

Ever since deep-sea hydrothermal vents were first discovered in the late 1970s, marine biologists have been fascinated by the unique animals that live in these areas. Hydrothermal vents often form near mid-ocean ridges, where hot lava rises up beneath the seafloor, causing the Earth’s crust to split apart. The rising lava heats water within these fractured subsurface rocks, which eventually seeps or gushes out of the seafloor, carrying minerals that are rich in sulfur and metals. Specialized bacteria live off of these hot, metal-rich hydrothermal fluids. Amazingly, a variety of deep-sea animals have found ways to incorporate the sulfur-loving bacteria within their bodies, so that they too can obtain nutrition from the chemicals flowing up out of the seafloor.

Exactly how the Yeti crabs fit into hydrothermal-vent ecosystems is still a mystery. Jones and his coauthors saw the crabs eating mussels that were cracked open when Alvin landed on the seafloor. But they also saw Yeti crabs holding their hairy claws out over plumes of warm water from hydrothermal vents. Because the crab’s arm hairs support large colonies of filamentous bacteria, the scientists speculated that the crabs might be “farming” the bacteria, perhaps as a source of food. This is not as far-fetched as it sounds—at least two other crab species have similar habits. Alternatively, lacking eyes, the crabs may use their hairs (which are actually flexible, hair-like spines called setae) as tiny chemical and physical sensors that help them find food or mates in the deep sea.

So far, scientists have only had a first-hand look at the one Yeti crab that was brought up by Alvin. This animal now resides in a sample jar at the French National History Museum in Paris, as part of its large reference collection of deep-sea crabs. Meanwhile, crab expert Joe Jones is just hoping for another chance to go back and see what else is lurking around the hydrothermal vents of the Pacific-Atlantic Ridge.

Research publication:
Macpherson, E., W. Jones, and M. Segonzac (2005). A new squat lobster family of Galatheoidea (Crustacea, Decapoda, Anomura) from the hydrothermal vents of the Pacific-Antarctic Ridge. Zoosystema, 27: 709-723.

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