Monday, 10 November 2014

The Dancing Kiwa Puravida (Yeti Crab)

Kiwa Purevida, one of the three yeti crab species
Kiwa Puravida
Credit: Andrew Thurber
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Crustacea
Class: Malacostraca
Order: Decapoda
Infraorder: Anomura
Family: Kiwaidae
Genus: Kiwa
Species: Kiwa puravida
Conservation Status: Not assessed
Common Name: Yeti crab

Meet Kiwa puravida, a recently discovered deep-sea dwelling decapod and one of three species informally known as "yeti crabs". The other two are Kiwa hirsuta and a creature commonly known as the "Hoff crab" which has yet to be described.

What is most interesting about this species is that individuals "dance" in unison to cultivate their own food! Wait...Whaaat? Keep on reading!

The species was discovered in June 2006, during a geological research cruise off the coast of Costa Rica, which aimed to study the ocean floor that belches out methane and hydrogen sulphide gas. Head of the expedition was Andrew Thurber, marine ecologist and now Assistant Professor at the Oregon State University.

While exploring the ocean floor Gavin Eppard, pilot of the submarine, noticed dozens of smalls crabs rhythmically waving their claws over active methane seeps and decided to collect one.

"He came up and just handed me this new species." said Thurber.

The discovery was made on a depth of about 1.000 meters (~3.280 ft).

The area where Kiwa Purevida was discovered
The area where K. Puravida was discovered

K. puravida and the other two yeti crab species are called this way due to the white, hair-like bristles that cover their claws and body. The bristles are full of symbiotic bacteria, which derive energy from the inorganic gases expelled by the seeps. The species is blind.

The female specimens collected to date had a carapace length between 4.9 and 24.5 mm, whereas collected males had a carapace length ranging from 7.4 to 38.6 mm.

Overall, K. puravida looks a lot like K. hirsuta, but differs in it at least ten anatomical features. The range of occurrence of the two species is about 6500 km away and the two occur in different habitats and depths. K. puravida was collected from a methane seep at 1000 meters deep whereas K. hirsuta was observed and collected at a greater depth (more than 2200 meters), next to a hydrothermal vent.

Kiwa Puravida specimen
Credit: Andrew Thurber

K. Puravida  feeds on the symbiotic bacteria, using comb-like mouthparts to harvest them from its bristles. In turn, these bacteria metabolise the hydrogen sulfide and methane produced by the seeps to feed themselves.

"It looks like the bacteria may use the seeps as stepping stones, to create this global connected population that consumes the energy coming out of seeps and vents." said Thurber.

Among other deep-sea creatures that make use of such symbionts, K. Puravida is unique in that it appears to actively wave its appendages over the vents in order to provide the bacteria with more nutrients. Actually, the crabs wave their claws in unison, in what seems to be a rhythmic dancing-like performance. This rhythmic movement stirs up the water around the bacteria, ensuring that fresh supplies of oxygen and sulphide wash over them and helping them to grow.

You can see this rhythmic movement in the video down below:

00:02 to 00:15, yeti crab feeds from the bacteria on its claws and body
00:15 to 00:24 Kiwa puravida  demonstrating the rhythmic waiving of the chelipeds.
00:24 to 00:32 Two individuals performing either a courtship or competitive display

Carbon isotopes and fatty acids in the body of K. Puravida match organisms that get their nourishment without the sun’s energy, rather than those that rely on photosynthesis. This suggests that K. puravida's feeds exclusively or primarily on seep bacteria, rather than surrounding photosynthesizing plankton.

"We clearly showed that this species isn’t using energy from the sun as its main food source. It’s using chemical energy from the sea floor." said Thurber.

Very little is known about the species' behavioral patterns. Thurber and his colleagues reported that the species demonstrates "intriguing intra-species interactions":

"An individual that appeared to have recently molted due to its minimal bacterial covering, began grappling with a larger specimen that it approached. This ended in a dominance display where the challenged individual forced the challenging individual off the carbonate outcropping while both individuals had their chelipeds spread apart. As decapods commonly reproduce after molting, as has also been observed in the hydrothermal vent S. crosnieri, the individual that was forced off may have been inseminated during this display or this may have been a behavior demonstrating how this species competes for space in areas of active seepage." extract from the study

Other Interesting Facts about  Kiwa Puravida
- Puravida derives from a Costa Rican Spanish saying (used to answer "How are you doing?" or to say "Thanks") and translates to "pure life". Thurber gave this name to pay homage to the place it was discovered.

References & Further Reading
- Thurber, A., Jones, W., & Schnabel, K. (2011). Dancing for Food in the Deep Sea: Bacterial Farming by a New Species of Yeti Crab PLoS ONE, 6 (11) DOI: 10.1371/journal.pone.0026243
- Roterman CN, Copley JT, Linse KT, Tyler PA, & Rogers AD (2013). The biogeography of the yeti crabs (Kiwaidae) with notes on the phylogeny of the Chirostyloidea (Decapoda: Anomura). Proceedings. Biological sciences / The Royal Society, 280 (1764) PMID: 23782878
- Ed Yong (December 2, 2011). "Yeti crab grows its own food". Nature

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