Scientists describe new species of crab that "farms" methane vents

Dec 03, 2011

A species of crab found a thousand feet below the surface of the Pacific Ocean near Costa Rica lives off the bacteria on its claws – bacteria that it fertilizes by waving them in methane and sulfide released from the seafloor.

This “farming” behavior was described for the first time in detail by the scientists this week in the journal PLoS One.

This new species of the Yeti crab, called Kiwa puravida, was first discovered in 2006, according to Andrew Thurber, a post-doctoral researcher at Oregon State University and lead author of the study. It is only the second member of the Yeti family of crabs – first discovered in 2005 – and illustrates how little scientists know about the deep ocean environment, the researchers say.

“We watched the crabs wave their claws back and forth in fluid from a methane seep, and rather than trying to capture , it appeared that they were providing food to the bacteria already growing on their claws,” Thurber said. “There isn’t sufficient food that deep that is derived from the sun’s energy, so vent and seep animals harness chemical energy released from the seafloor.

“These bacteria are specialists and can be found on a variety of crustaceans – crabs, shrimp and barnacles – near seeps and vents," added Thurber, who is in OSU's College of Earth, Ocean and Atmospheric Sciences. “But we hadn’t before seen that kind of ‘farming’ behavior in which the host waves its symbionts in seep fluid.”

Thurber, who did much of the research as a doctoral student at the Scripps Institution of Oceanography, wasn’t part of the 2005 that found the first Yeti crab, but participated in the 2006 expedition that discovered Kiwa puravida, and follow-up cruises in 2009 and 2010 that collected the crabs using the submersible Alvin.

Having the specimens allowed the scientists to more closely examine the bacteria on their claws and run their genetic code through GenBank – an international database that includes thousands of species of bacteria. They discovered that it is most similar to bacteria found on crabs and shrimp living near hydrothermal vents.

“We don’t know for certain whether hydrogen sulfide alone fuels this species’ symbionts,” Thurber said, “but we suspect it may use both hydrogen sulfide and methane released from the seafloor to exist so far from the sun.”

Thurber said symbiotic behavior in nature is common, but few animals are known to behave in quite the same way as Kiwa puravida. Some organisms, including mussels and tubeworms, have symbionts inside of them that allow them to harness chemical energy, while others that do not have symbionts – including barnacles – wave their appendages to grab food as it goes by. This new species is the only one that combines the two, by using symbionts on its appendages and waving those bacteria-laden appendages in seep fluid to capture as a food for themselves.

Lipid and isotope analyses showed that these epibiotic bacteria are the crabs’ main food source, though Thurber said they may be getting a small amount of sun-derived energy from dead plankton that have filtered down through the water column.

Thurber said the crabs harvest the bacteria growing on their claws by using a specially adapted appendage to scrape the bacteria off their bodies and bring it to their mouths, and then continually waving their claws near methane seeps to boost the bacteria’s productivity.

Only one specimen of the original Yeti crab, K. hirsuta, has been collected and that was near a hydrothermal vent. About 30-40 specimens of Kiwa puravida have been examined and the scientists believe they may exist at similar methane seeps.

“Since this entire family of wasn’t even discovered until 2005, there is a strong possibility other species are out there,” Thurber said.

Other authors on the study are W. Joe Jones of the University of South Carolina and Kareen Schnabel of the National Institute of Water and Atmospheric Research in Wellington, New Zealand.

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User comments : 8

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Isaacsname
5 / 5 (3) Dec 03, 2011
I haven't even read the article yet, just wanted to say, there's a sad irony that creeps over me to read a fascinating title like this with an ad for fresh Alaskan crab under it.

Maybe a little distasteful .
OvertOddity
not rated yet Dec 03, 2011
Ad blockers FTW.
Isaacsname
5 / 5 (1) Dec 03, 2011
>facepalm< That was easy, thanks.
plasticpower
3 / 5 (2) Dec 03, 2011
It would be cool to read about all the species that "farm" in various ways. Ants for example.. Very interesting article, never thought something wonky like this could evolve. Wonder how long the crabs have been doing this for and how they figure this behavior out after they're born.
Pirouette
1 / 5 (6) Dec 03, 2011
Question is: how do the crabs KNOW that the bacteria are growing on their claws? An exoskeleton doesn't provide much sensory stimulation. If the bacterial colony grows so large as to be observed easily by the crab even in the dark, or the colony has a certain odor that's detectable, it might be said that the crab has good perception at dinner time.
Isaacsname
not rated yet Dec 04, 2011
Could have been accidental/opportunistic, crabs clean themselves like bugs, kind of. For them to make a connection between the bacteria on their arms and the needed nutrition for the growing of the microbes though,...it's just as perplexing as asking how the ants knew about growing fungus.

Maybe we are making assumptions..

If we assume the crab is intelligent enough to farm the microbes in the manner it does, we could also assume there's a small chance it's trying to wash them off by the same method.

A crab farming and a crab washing it's hands are equally absurd though :P

gopher65
not rated yet Dec 04, 2011
More likely it is just an OCD behaviour that the crabs unwittingly developed by random chance. It just happened to be a positive behaviour, and helped them survive. The ones that "washed" themselves in the methane vents were more likely to survive, so they are the ones we see today.

The same thing could have happened in humans. Imagine 1000 years ago that... say... 10% of the population of Venice had by random chance (and inbreeding) become OCD. Pretend that they were fanatically clean, washing themselves raw. Not out of a sense of cleanliness, but due to their OCDness. This remains constant for a few hundred years, with a small proportion of the population being OCD.

The the black plague hits. The people that are OCD are relatively immune to the disease due to their obsession (*not* due to any intelligent action on their part), and are relatively unaffected. As the people around them are dropping like flies, the OCDers are happily breeding away.

That's what happened to the crabs.
Midwesterner
1 / 5 (1) Jan 25, 2012
As I read about the creation of the sea creatures in Genesis 1:20 I am amazed, but not surprised that even now we are discovering additional species of underwater creatures. This shows how awesome and expansive the creative power of God is. He knew when He created each and every living creature what it needed to survive. He also knew that thousands of years after He created the sea creatures on the 5th day we would still be discovering species that have never been seen by human eyes. He really meant what He said when He said "Let the waters teem with swarms of living creatures." (Genesis 1:20)

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