Discovered in the deep: The Hoff crab with hairy chest

In 2005, researchers exploring more than a kilometer underwater south of Easter Island in the South Pacific found strange-looking white crabs with long, hairy arms. They called them yeti crabs.

Several years later, in 2010, aboard a research ship in the Southern Ocean, surrounded by icebergs, fin whales and penguins, another team of scientists thought about the deep-sea crabs they had just found 2,500 meters below the surface. These were a variety of yeti crabs, ranging from miniature to fist-sized, but instead of having hairy arms, they had lush hairy chests.

The ocean is one of the world’s last truly wild spaces. It abounds with fascinating species that sometimes seem to border on the absurd, from fish that look up through transparent heads to golden snails with iron armor. We know more about deep space than deep oceans, and science is only beginning to scratch the surface of the rich diversity of life in the deep.

As mining companies push to industrialize the seabed and global leaders continue to wrangle over how to protect the high seas, a new Guardian Seascape series will profile some of the most recently discovered weird, wonderful, majestic, ridiculous, hardcore and sensational creatures. They reveal how much there is still to learn about the least known environment on Earth – and how much there is to protect.

The researchers considered naming it after 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 on the 90s TV hit Baywatch, who won and the “Hoff Crab” was christened.

Those hairy arms and chests are key to the crab’s survival in one of Earth’s most extreme habitats: fiery hydrothermal vents, also known as black smokers.

Yeti and Hoff crabs do not hunt around for prey or hunt for dead scraps, like most crustaceans. Instead, they graze on colonies of microbes that grow in their fur. These microbes utilize energy from toxic chemicals, such as methane and hydrogen sulphide, which are rolled out of the chimney.

The microbial process known as chemosynthesis is a dark alternative to plant-based photosynthesis, and it takes place in the pitch black of the deep sea without the need for sunlight. “The adaptability of life is astonishing,” says Roterman.

A few years ago, when asked by a journalist which of his natural history curiosities he most cherished, David Attenborough said he was particularly fond of the Hoff crab encased in resin, like a paperweight, which sits on his desk. It was a gift from Roterman and a reminder, he said, that animals exist that until recently have 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 climbing up ventilation chimneys.

“We observed them sparring with each other, measuring up against each other and using their claws as a caliper,” says Roterman. There can be more than 700 Hoff crabs per square meter, with the males jostling for prime real estate, fighting to get closest to the chemical-rich fluids that bathe their microbes and provide more food.

They form mini-cities under the sea, coexisting in a small area where it is warm enough to live, but not hot enough to boil.

Related: Discovered in the deep: the snail with iron armor

Life for female Hoff crabs is quite different. With clutches of fertilized eggs stuck to their bodies, they cannot afford to hang around the valves where the seawater is low in oxygen and their young would soon suffocate. So expectant females creep away in the cold darkness a few meters from the chimneys. There they sit and starve, lacking chemicals to feed their microbial fur farm.

They are paralyzed 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 the females breed only once and then die, or whether they return to the vents to find another mate. “We have no idea if it’s a one-way trip,” he says.

The low oxygen around hydrothermal vents may put yeti and Hoff crabs at particular risk of the climate crisis. The warming ocean will probably become more stratified and stagnant, with less mixing of oxygen-rich shallow seawater down into the depths.

“We know this is already happening,” Roterman says, “and that means some of the first deep-sea species to go extinct … could be hydrothermal vent species.”

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