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04 January, 2012

More from the Abyss: Wave Them Big Hairy Arms

Kiwa puravida male holotype: (A) Dorsal view. (B) Ventral view (A and B Scale bar = 10 mm; Credit: Shane Ahyong, NIWA Wellington). (C) in situ next to Bathymodiolin mussels (D) Scanning Electron Micrograph of a detail of K. puravida's 3rd maxilliped and the comb-row setae which it uses to harvest its bacteria (scale bar = 150 ┬Ám credit; Shana Goffredi, Occidental College]. (E) Setae covered by bacteria from 3rd pereopod (see Figure 4E for scale). (F) Dense aggregation in situ. (G) Shipboard photo of K. puravida using its 3rd maxilliped to harvest its epibiotic bacteria. (H) Comb-row setae with bacteria filaments stuck among combs (indicated by arrow).
doi:10.1371/journal.pone.0026243.g001
Oh yeah, that's a Yeti Crab. My new favorite species. This one is from the waters off Costa Rica, where you least expect a Yeti, which only makes it better.

You won't run into one, lazing on the beach or even scuba diving. Unless you know where the deep-sea methane vents are, and have the right submersible, you'll never see a Yeti Crab except on screen. It is another one of those creatures who live where the sun don't shine, a denizen of the abyssal deep, a realm I've waxed un-poetic about before.

A couple of cool things about Yeti Crabs: they occupy hydrothermal vents as part of a fauna that differ from those worms we've come to expect, and they are farmers. The Yeti's genus was only discovered in 2005, and in the past year scientists found an incredibly dense population of them near Antarctica (check out this article), at vents where the usual swarms of shrimp and vestimentiferan worms were absent, but new species of barnacles and snails were discovered. 

Reading this, my initial thought was that hydrothermal vents, being rare and widely dispersed, might each be a world unto itself, populated with a unique fauna found nowhere else, isolated. But in this article reviewing the past decade of research, that turns out to be only partly true. Yes, scientists now believe that there are entirely new biogeographic regions centered on vents, but they also have begun to collect evidence for dispersal between vents, deep fracture zones and currents that allow larvae from one vent to find and colonize another. So there are species of Yeti Crabs in the Antarctic and Indian Oceans, as well as those off of Costa Rica. Between these far-flung worlds, benthonauts go where no man has gone before.

In the Antarctic, where they were so thick that scientists said they looked like piles of skulls on the ocean floor, and elsewhere, the Yeti Crabs prove to be not abominable, but peaceful. Most crabs would eat you as soon as look at you (assuming you're already dead and ripe enough to scavenge), and have no hesitation to use their chelipeds to capture and dismember prey. But not the Yeti. No, this genus grows hair on its pincers, forming a field in which bacteria  thrive. It feeds the bacteria by waving its hairy arms (the first species documented was dubbed Kiwa hirsutus) in the flow of hydrothermal vents. Then it uses a specially adapted appendage to scrape off the bacteria, its only known food. 

The earth farts, the crab waves its claws in the methane, and everyone is happy. Sounds gross, but how different is it than humans using cowshit and urea to grow food? It's certainly more efficient, dining way down on the food chain, and it has the benefit of digesting methane and hydrogen sulfide before they can contribute to our greenhouse gas problem. My main hope is that it makes the crab taste like farts, so we don't start harvesting them for our own food.


The information above came from this article:

"Dancing for Food in the Deep Sea: Bacterial Farming by a New Species of Yeti Crab"

The article was written by:
Andrew R. Thurber1*, William J. Jones2, Kareen Schnabel3

You can fund the article at:

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