The first species of kiwa crab wasn’t discovered until 2005, and another was recently announced. But neither of those was found living crunched together in anything like the mobs that Rogers’s group found. Like many vent species, the crabs’ bodies are covered by bacteria that feed on vent chemicals and that in turn are eaten by the crabs. The researchers saw the crabs, some as big as a fist, fight over position and occasionally burn themselves trying to hold their bacteria-laden appendages and undersides as close as possible to the nourishing vent outflow.
The researchers also saw thickets of pencil-length barnacles, another new species, growing more densely than similar species the team had seen at other vents. In addition, a new snail species, with a bright red foot, was crammed a hundred to a square foot.
At the same time, none of the species that dominated every other vent site were there, such as shrimp and tube worms.
Based on genetic analyses, the team believes the vent life they discovered in 2010 is so distinct that it constitutes a cluster of species not found anywhere else. The team published its findings Tuesday in the journal PLoS Biology.
With further study, the researchers hope to better understand the evolution of life on hydrothermal vents, how those life-forms spread around the planet and what determines where they live now. “Something different happened there,” said Tim Shank, a Woods Hole deep-sea biologist who was on the team, “and that tells us about the processes that shape life.”
Many of the scientists who made these discoveries have just returned from exploring new vents in the southwest Indian Ocean. They found what appears to be another new species of kiwa crab, although tests have yet to confirm that. But these crabs were sparse. Shrimp were there, though not in swarms.
“Right now, the Southwest Indian Ridge looks a bit like a crossroads,” said Jon Copley of the University of Southampton, who led the Indian Ocean vent work and was also on the Southern Ocean team.
Now the scientists have more questions with which to wrestle. If, for instance, the Southern Ocean is uniquely isolated due to colder waters or some other factor, then why are the kiwas in the Indian Ocean, and what kept the shrimp away from the Southern Ocean? “The story is obviously pretty complicated,” Rogers said. “There must be connectivity, or at least there has been connectivity in the past.”
Schrope is a freelance writer and former oceanographer who is completing a book on the Gulf of Mexico oil spill.