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Hydrothermal vents sometimes colonized from afar
Deep-sea currents can waft larvae hundreds of kilometersBy Sid Perkins Web edition : Friday, February 26th, 2010 Text Size Enlarge
Aimless driftersThe larvae of species found at hydrothermal vents, such as the limpet Ctenopelta porifera (larva at left, adult at right), can colonize suitable habitats after being carried hundreds of kilometers by seafloor currents.S.E. Beaulieu, WHOIPORTLAND, Ore. — Field studies at a hydrothermal vent system where all life was snuffed out by a massive undersea volcanic eruption reveal that these habitats can be repopulated in a matter of months by larvae from distant vents.

In late 2005 and early 2006, a swarm of earthquakes rocked a 15-kilometer-long portion of the East Pacific Rise, a deep submarine ridge south-southwest of Acapulco, Mexico. That portion of the rise, which in turn is part of a network of mid-ocean ridges that encircle the globe, hosts hydrothermal vent systems that many researchers have long studied.

When scientists returned to the area four months after the quakes, cameras sent to the seafloor revealed that a volcanic eruption had smothered spots as far as two kilometers from the ridge with lava. “All of the organisms in the region were eradicated,” said Lauren Mullineaux, a biological oceanographer at the Woods Hole Oceanographic Institution in Massachusetts. That devastation provided a natural laboratory to see how long it would take for organisms to recolonize the vent systems, she explained in a February 25 presentation at the American Geophysical Union’s Ocean Sciences meeting.

Water samples taken near the vents in May 2006 contained the larvae of Ctenopelta porifera, a rock-clinging gastropod called a limpet. By July, these fast-growing creatures had colonized the rocks around the eruption-sterilized vents; by October, they were mature and reproducing. The presence of C. porifera at these vents was striking, Mullineaux said, particularly because the nearest hydrothermal system known to host that species is located more than 300 kilometers away.

Previous lab studies suggest that larvae of vent-hosted species drop into a state of suspended animation if they drift out of warm waters near the vents and into the near-freezing conditions typically found in the deep sea (SN: 11/24/01, p. 331). Such larvae can exist in that state for about 30 days before their nutritional reserves run out, Mullineaux said.

On the east flank of the ridge where the recolonized vent systems are located, currents along the seafloor flow from the north — the direction of the nearest vent that hosts C. porifera — at a speed of about 10 centimeters per second. At that rate, a larva could be wafted about 300 kilometers in a month, said Andreas Thurnherr, a physical oceanographer at the Lamont-Doherty Earth Observatory in Palisades, N.Y. He and a colleague reported analyses of currents along the East Pacific Rise at the meeting on the same day as Mullineaux’s presentation.

“It’s clear that the flank currents play a major role in larval dispersal” from one hydrothermal vent system to another, agreed Dennis McGillicuddy, an oceanographer at the Woods Hole Oceanographic Institution.