An otherworldly gardener
In March 2005, scientists exploring the Pacific-Antarctic Ridge made an unexpected discovery. Aboard the research vessel Atlantis, the deep-sea submersible Alvin descended to a depth of 2,200 meters (7,200 feet) near hydrothermal vents. There, approximately 1,500 kilometers south of Easter Island, researchers found a crustacean entirely new to science. Measuring about 15 centimeters (5.9 inches) long, the creature was a ghostly white decapod, a relative of crabs and hermit crabs. Its most remarkable feature was a dense covering of silky, blonde, hair-like structures on its claws and legs.
This unique appearance immediately earned it the nickname "yeti crab." The animal's eyes are strongly reduced and lack pigment, rendering it blind, a common adaptation for life in the darkness of the abyssal zone. The discovery was so distinct from any known species that scientists had to create an entirely new taxonomic family for it: Kiwaidae. The official scientific name given to the crab is Kiwa hirsuta. "Kiwa" refers to a Polynesian goddess of shellfish, and "hirsuta" is Latin for "hairy."
Cultivating life in the dark
The "hair" on Kiwa hirsuta is not hair; it is fields of bristle-like structures called setae. These setae host vast colonies of filamentous bacteria. The crab lives near hydrothermal vents that spew superheated, mineral-rich water into the cold, deep ocean. This fluid contains chemicals like hydrogen sulfide and methane, which are toxic to most life forms but are a source of energy for certain microbes. The bacteria on the crab's claws are chemosynthetic, meaning they create organic matter from these chemicals, much like plants use sunlight for photosynthesis.
Researchers have observed the crabs rhythmically waving their claws through the water. This motion is a form of farming. By waving its claws, the crab "fertilizes" its bacterial gardens, bathing them in a steady flow of the oxygen and chemical nutrients they need to grow. The crab then uses specialized, comb-like mouthparts to scrape the cultivated bacteria off its setae for food. While the bacteria are its primary food source, the yeti crab is thought to be an omnivore, also feeding on mussels and other small organisms when available. This farming behavior is an adaptation to an environment where food is scarce and sunlight for photosynthesis is nonexistent.