In 2005, scientists exploring more than a mile underwater south of Easter Island in the south Pacific, found odd-looking white crabs with long, hairy arms. They named them yeti crabs. Several years later, in 2010, onboard a research ship in the Southern Ocean, surrounded by icebergs, fin whales and penguins, another science team contemplated the deep-sea crabs they had just found 2,500 metres beneath the surface. These were a variety of yeti crab, ranging from thumbnail- to fist-sized, but rather than having hairy arms they had luxuriant hairy chests. The scientists considered naming it after the James Bond actor Sean Connery, says Nicolai Roterman, a deep-sea ecologist at Portsmouth University . But it was David Hasselhoff, from his days as a Los Angeles lifeguard in the 90s TV hit Baywatch, who won out and the “Hoff crab” was christened. Those hairy arms and chests are key to the crabs’ survival in one of the Earth’s most extreme habitats: scorching hydrothermal vents, also known as black smokers. Yeti and Hoff crabs do not chase around after prey or scavenge for dead scraps like most crustaceans. Instead, they graze on colonies of microbes that grow within their fur. These microbes harness energy from toxic chemicals, such as methane and hydrogen sulphide, that are churned out of the vent chimney stacks. The microbial process known as chemosynthesis is a dark alternative to plant-based photosynthesis and it goes on in the pitch black of the deep sea with no need for sunlight. “The adaptability of life is astounding,” says Roterman. A few years ago, when asked by a journalist which of his natural history curiosities he treasures the most, David Attenborough said he was especially fond of the Hoff crab encased in resin, like a paperweight, that sits on his desk. It was a gift from Roterman and a reminder, he said, that animals exist that have until recently had no contact with humans and have no concept of our existence. Much of what is known about these unusual crabs comes from video beamed up from remotely operated underwater vehicles exploring hydrothermal vent fields. Footage shows hundreds of male Hoff crabs clambering up vent chimneys. “We observed them sparring with each other, sizing up against each other and using their claws like callipers,” says Roterman. There can be more than 700 Hoff crabs per square metre, with the males tussling for prime real estate, vying to get nearest to the chemical-rich fluids that bathe their microbes and yield more food. They form mini cities under the sea, co-existing in a tiny area where it’s warm enough to live but not hot enough to boil. Life for female Hoff crabs is quite different. With clutches of fertilised eggs stuck on to their bodies they cannot afford to hang around the vents where the seawater is low in oxygen and their young would soon suffocate. So expectant females crawl away into the cold dark a few metres from the chimneys. There they sit and starve, lacking chemicals to nourish their microbial fur farm. They become paralysed by the cold water and are easy prey for predators. “We found these weird seven-armed starfish that would patrol the perimeter and eat the females,” says Roterman. One of the many mysteries that still surrounds Hoff crabs is whether females breed just once then die, or if they make it back to the vent chimneys to find another mate. “We have no idea if it’s a one-way trip,” he says. The low oxygen around hydrothermal vents could put yeti and Hoff crabs at particular risk of the climate crisis. The warming ocean is likely to become more stratified and stagnant, with less mixing of oxygen-rich shallow seawater down into the deep. “We know this is happening already,” Roterman says, “and it means that some of the first deep-sea species that could go extinct … could be hydrothermal vent species.”