Deep-sea hydrothermal vents are springs that can spew out water at temperatures of more than 800 degrees. Loaded with chemicals and minerals from the rocks below, the hot water mixes with the much colder seawater in a chemical frenzy that often creates billowing black plumes. Some of the minerals form chimneys around vents that can grow several stories tall.
Geologists discovered the first hydrothermal vents in the Pacific in 1977, near the Galapagos Islands. So unprepared were they to find life in such a hostile place that their team included no biologists, and they packed few biological supplies. But there were huge worms living in tubes, some as tall as a person, dominating the vents, alongside plots of massive clams. The geologists pickled samples of the strange animals as best they could, in some cases using Russian vodka they happened to have on hand.
Later work revealed that the tube worms and other vent animals got their food from bacteria that feed on the chemicals in a vent’s outflow. It was the first ecological system found to use chemicals, rather than sunlight, as a foundation.
For years, most scientists believed they would find hydrothermal vents only in the Pacific, the most geologically active ocean. But in 1985, a team from the National Oceanic and Atmospheric Administration found vents along the submerged mountainous ridge that runs down the middle of the Atlantic. Instead of a field of tube worms, these vents were crawling with hundreds of thousands of shrimp.
Further vent discoveries have involved dozens of new species every year, but the sea-vent life was always dominated by the same general type of animals.
The Southern Ocean, which surrounds Antarctica, has only recently been a focus of deep-sea exploration. It’s particularly difficult to reach, and its waters are treacherous, with storm swells regularly hitting 50 feet. Chris German, a geochemist at the Woods Hole Oceanographic Institution in Massachusetts, was the first to discover deep-sea vents in that area in 1999, after detecting the telltale water plumes, but he was unable to explore them for more than a decade.
In 2010, a group that included German used a remotely operated vehicle to maneuver about 8,000 feet down into the icy sea and send high-definition video from the forbidding zone to a British research vessel on the surface. The team’s very first view was the sort that has always driven explorers. Shouts from the scientists watching the monitors quickly drew everyone on board to gaze upon a landscape blanketed by what they quickly realized was a new species of kiwa crab, also known as the yeti because of its hairy body.
“They almost looked like a pile of skulls sitting on the seabed,” said the team’s leader, Alex Rogers, a deep-sea biologist at Oxford University. “It was an amazing, amazing sight.”
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.