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Yeti crabs have figured out how to live without the sun! All they need is their fuzzy arms, bacteria, and the bizarre, dark oozings of the deep.

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#Crabs #HydrothermalVents #BizarreBeasts #carcinization #Carcinisation
Most of life on Earth, including us, ultimately depends on the sun for energy. Plants and other photosynthetic organisms like phytoplankton turn sunlight into chemical energy, which is then consumed and used by all the things on land and in the ocean that eat these photosynthesizers, and so on up the food chain. It’s a pretty good system, but it’s not the only one. Because, in some of our planet’s more extreme environments, photosynthesizers, and sunlight, are in short supply. Which means that, in places like the deep, dark seafloor, there are bizarre beasts who get all or most of their energy from toxic gases bubbling out of cracks in the ocean’s crust, instead. And how they manage that is about as strange as the critters themselves. The sun’s up there thinking, “I’m so important!” Well, so are the bizarre, dark oozings of the deep. And what we’ve found down there is even weirder than we thought.

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 Say hello to the crabs in the genus Kiwa, also called YETI CRABS, because just look at those white, furry arms. There are six known species of these little dudes, ranging from the legitimately hairy-looking Kiwa hirsuta to the only somewhat-fuzzy Kiwa tyleri, and there could still be more new species out there. The first yeti crab was only discovered in 2005! And while they’re usually called crabs, they’re actually just squat lobsters, more crab wannabes, it means they’re kinda-lobster shaped, but with their tails permanently tucked up under their bodies.

Today, yeti crabs are only found in two very particular kinds of deep-sea environments, hydrothermal vents and methane seeps. Five species live on vents and one lives on a seep. And while they’ve been found in these kinds of habitats around the world, only one species is seen at each location. Based on how the six species are related to each other, it looks like the yeti crab family split off from their closest relatives somewhere in the East Pacific around 40 million years ago and may have originally lived only on hydrothermal vents. And where they’re are found today, geographically,is probably the result of plate tectonics over those 40 million-ish years, specifically, where the mid-ocean ridges have opened and closed, creating and destroying hydrothermal vent habitats, and causing regional extinctions and new radiations of yeti crabs over time.

Now, two big differences between a hydrothermal vent and a cold seep are temperature and longevity. Vents are hot and relatively short-lived environments, while seeps are around the same temperature as the surrounding water and tend to stick around for longer. And temperature really matters! For example, Kiwa tyleri lives in the Southern Ocean, between South America and Antarctica. It can only exist in a tiny “thermal envelope”of a few square meters next to the hydrothermal vents there, it’s just too cold to get any farther away from that heat source. I totally get this, I live in Montana. And because these thermal envelopes are so tiny, there can be more than 700 crabs per square meter around these vents! Which definitely sounds like something you’d hear in an ad for an all-you-can-eat seafood buffet.It also means that, sadly, when females of this species scuttle away from the vents to reach the cooler waters they need for brooding their eggs, they usually starve and die. How the babies survive and eventually get back to the warmth of the vents is still a mystery, though it looks like they spend a relatively long time as negatively buoyant larvae, hanging out near the sea floor.

And here’s another kinda-weird thing: both the vent-living Kiwa tyleri and the methane seep-living Kiwa puravida seem to have very similar lifestyles, even though they inhabit very different environments. Both species of crab have body parts covered in setae, or stiff hair-like bristles. They’re mostly just on the claws of Kiwa puravida, but Kiwa tyleri also has them all over its legs and belly, too. And on these setae live bacteria that are capable of turning toxic gases, like methane and hydrogen sulfide, into glucose through chemosynthesis. Kiwa puravida even waves its claws directly over the methane seeps, probably to help increase the productivity of the bacteria. Because the crabs aren’t just providing housing to these bacteria. They’re farming them to eat. They’ve even got specialized comb-like bristles on their mouth appendages that they use to scrape bacteria off of their setae and into their mouths. And the researchers studying Kiwa puravida were able to confirm that the bacteria are its main source of food by analyzing the carbon isotopes and fatty acids in its tissues.

 In some ways, you are what you eat, and the carbon and fatty acids in the crab were a match for its bacteria and not for the plankton living around the methane seep. This is where the whole not relying on the sun for energy thing comes in, except there’s a little bit of a twist. See, the source of the hydrogen sulfide gas at the hydrothermal vents is the planet’s crust. And most species of yeti crab, and their arm-hair bacteria farms, live at these vents and subsist on this source of chemical energy. Except for Kiwa puravida that lives on the methane seeps. Because the chemicals bubbling out of the seeps are actually leaching out of petroleum deposits. And these started off as organic materials that got their energy from the sun! So, as wild as it is that there are ecosystems out there that exist pretty independently of the sun, it’s also wild that, in the deep ocean, ancient photosynthesis is still powering organisms alive today.

If I have made you a believer in the yeti “crab,” now’s your chance to get your claws on one of these awesome pins! The Bizarre Beasts pin club subscription window is open through the end of December 6th. When you sign up, you’ll usually get the newest beast pin in the middle of the month and the pins after that around the time each new video goes live. Shipping this month might take a little longer, so we can’t guarantee the crab in time for the holidays. While you wait, check us out on Twitter @BizarreBeasts, and on Instagram and Facebook @BizarreBeastsShow, where we’ll share more fun critter facts that didn’t make it into the episode! And this month, like every month, profits from the pin club go to support our community’s efforts to decrease maternal mortality in Sierra Leone.

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