Currents reach deep for seafloor larvae

Surface waters circulate more than a mile down

Whirling ocean currents whipped up by the wind can reach hydrothermal vents more than a mile deep and transport intrepid bottom dwellers to distant realms, oceanographers report in the April 29 Science.

LAVA LARVAE Currents stirred up by winds at the ocean’s surface may carry larvae long distances to repopulate hydrothermal vents after catastrophes. © Woods Hole Oceanographic Institution

In late 2005 or early 2006, an underwater eruption decimated several vents south-southwest of Acapulco, Mexico, along a deep ocean ridge, the East Pacific Rise (SN Online: 2/26/10). Baby limpets recolonized the area — a species that normally lives at another vent system more than 300 kilometers away.

Searching for fast currents that could transport these larvae over long distances, Diane Adams, an oceanographer at the Woods Hole Oceanographic Institution in Massachusetts, looked eastward. In the coastal waters of Nicaragua and Costa Rica, strong winds from nearby mountains can stir up huge circular currents, called mesoscale eddies, that roll across the Pacific Ocean. 

“When we think of eddies, we tend to focus on the upper ocean, where all the biological action is,” says Claudia Benitez-Nelson, an oceanographer at the University of South Carolina in Columbia. “It’s fascinating and compelling to think that they play a role at depth.”

During February and March of 2005, an eddy about 375 kilometers across passed over another vent monitored by the Woods Hole team. Current speeds near the vent almost tripled. Traps checked before and after the event showed that many of the snail and limpet larvae had been swept away.  

Most of the departed larvae likely died lonely deaths in the deep ocean. But a lucky few may have ridden the currents to new homes.

“Even if 1 percent or less can get to another vent, that could be enough settlers to make a new community,” says Adams.

She suggests that other large eddy systems — such as those that cross the Mid-Atlantic Ridge — could also participate in this game of larval leap frog.

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