At deepest hydrothermal vent yet found, an 'awe-inspiring' view

Scientists have found a hydrothermal vent community three miles beneath the sea near the Cayman Islands. Other vents have led to the discovery of new and exotic creatures.

Scientists taking part in a global Census of Marine Life have discovered off the Cayman Islands the deepest sea-floor hydrothermal vent community yet known.

Researchers have not yet formally published the results of their expedition. But elsewhere, "black smokers" – towering, two-story-tall vents spewing mineral-rich, superheated water into the inky darkness around them – are oases of life for organisms ranging from bacteria to crabs and giant tube worms.

The sight of these vents three miles beneath the surface, as seen through videos from an unmanned submersible dubbed HyBIS, "was awe-inspiring," according to a statement from Jon Copley, a University of Southampton marine scientist and one of the expedition's leaders.

IN PICTURES: Hydrothermal vents

While new species crop up with regularity from tropical rain forests, those discoveries are often incremental. "Invariably, it's going to be an insect, and chances are it's going to be a beetle," says Paul Tyler, another of the leaders of the expedition, during a phone conversation from his cabin aboard the British research vessel RSS James Cook.

By contrast, "in the deep sea, chances are you're going to find something completely new," he says, noting that discoveries in the deep sea during the past century have led scientists to create three new phyla – biological categories for never-before-seen body types.

Other discoveries have pushed the bounds of the exotic: for example, the "yeti crab" discovered in 2005 living at hydrothermal vents 900 miles off Easter Island. National Geographic exclaimed that the feathery limbed crab "is so extraordinary that a new taxonomic family had to be invented for it."

"The deep sea is likely to be the reservoir of highest biodiversity on the planet," says Dr. Tyler

A biological surprise

The newly found black smokers rise from the Cayman Trough. It's an undersea rift valley that runs between Jamaica and the Cayman Islands and forms part of the boundary between the Caribbean and North American Plates.

The location falls into a relatively new category of undersea features of Earth's crust – an ultra-slow spreading center – that only a decade ago seemed of little biological interest.

Ultra-slow spreading ridges replenish the crust with new material, as do their more energetic counterparts. But the new crust is generally much cooler than the crust welling up from other, faster-paced spreading centers such as the East Pacific Rise or the mid-Atlantic Ridge.

Essentially these ultra-slow centers – which include the Arctic's Gakkel Ridge and the Southwest Indian Ridge in the southern Indian Ocean – were thought to be too cool to generate the hydrothermal vents. But during the past decade, expeditions to these locations have found otherwise.

Scientists with the census realized "that we had to understand how the Cayman Trough fit into the biogeography and the chemistry of the global ocean," Tyler says.

The research by Tyler and his colleagues builds on an expedition last fall by the Woods Hole Oceanographic Institution (WHOI). It conducted an initial cruise to the trough as part of the Census of Marine Life's so-called ChESS project, which aims to catalogue marine organisms at undersea hydrothermal vents.

But the cruise ended with only the tantalyzing chemical fingerprints of hydrothermal activity in water samples brought up from the deep ocean, notes Chris German, a WHOI marine scientist who led that expedition. His team's data isolated the black smokers' location to within a radius of about 800 feet, he explained during a presentation at last fall's meeting of the American Geophysical Union in San Francisco.

Armed with that information, Tyler and his colleagues were able to focus their search on that area.

Understanding the deep-sea world

As scientists find more vent communities, broader questions are emerging, says Ronald D'Or, senior scientist for the census. While some creatures appear to be common among many of these deep-sea ecosystems, others appear to be unique to their locations, he says.

For the Cayman Trough, genetic comparisons between organisms there and those found on the East Pacific Rise might yield insights into organism migration, since roughly 30 million years ago, what is now the Caribbean Sea was a patch of ocean that connected the Atlantic and Pacific.

This week, scientists reported such vent-community migrations – on a much smaller scale. Researchers at WHOI and the Lamont-Doherty Earth Observatory at Palisades, N.Y., reported the discovery of sea snails at a hydrothermal site on the East Pacific Rise where the snails had never been seen before.

An volcanic eruption had wiped out the previous assembly of organisms at this site. And the nearest known snail population was some 215 miles north.
Modeling studies suggested the otherwise slow-swimming larvae were propelled to their new home by current "jets" along the crest of the ridge. That colonization "radically altered the community structure" at the post-eruption site, according to Lauren Millineaux, a senior scientist at WHOI.

The results appear in yesterday's issue of the Proceedings of the National Academy of Sciences.

IN PICTURES: Hydrothermal vents