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Giant Tubeworms Probed for Clues to Survival

Bijal P. Trivedi
for National Geographic Today
October 28, 2002
 
Along the Galápagos Rift, off the storied Galápagos Islands, is a hotbed of volcanoes and hydrothermal vents that spew boiling soups of metals, salts, and poisonous gas. These seemingly inhospitable vents are home to some of the toughest, most exotic life on Earth, including clams and mussels as big as dinner plates and bright-white tubeworms six feet long.

The giant tubeworms, discovered during a pathbreaking exploration of the rift in 1977, forced a rethinking of life on the ocean floor. The rift lies 300 miles (500 kilometers) north of the Galápagos Islands, and the seafloor extends 8,000 feet (2,500 meters) below the waves.

"The rule of thumb was that only small organisms could occupy the deep sea," says Tim Shank, a biologist at the Woods Hole Oceanographic Institution in Massachusetts and co-director of a recent expedition to the Galápagos Rift organized to mark the 25th anniversary of the hydrothermal vent discovery.


"We knew there were microbial communities that could survive without sunlight or oxygen, but tubeworms are massive life-forms," he added.

The recent expedition focused primarily on tubeworms, which have developed unique adaptations to their environment.

These worms live in pitch-black ocean depths in water laced with acid and toxic gas—harsh conditions that may resemble those in which life first evolved. Scientists want to decode the tubeworms' survival skills.

No Stomach, No Gut, No Eyes

Kang Ding, a geochemist at the University of Minnesota at Minneapolis, devised a new sensor to explore the worm's world inside and out. "This is the first time we have tried to put a sensor into the actual worm," Kang says.

To deploy Kang's new sensor, scientists descended to an ocean-floor vent inside Alvin, a deep-sea submersible able to withstand the crushing pressures of two-mile (three-kilometer) depths.

The pilot in the submersible maneuvered Alvin's robotic arm to slide the probe into a worm, inch by inch. Every four seconds the probe measured the temperature, acidity, and concentration of two gases (hydrogen and hydrogen sulfide), all of which are critical to the survival of the tubeworms.

The new probe enhanced the scientists' appreciation of the tubeworm's uniqueness.

"Actually, the tubeworm has no stomach, no gut, no eyes. It is basically a bag of bacteria with an aorta and gonads," Shank says.

The worms live at the interface of two worlds. The tip of the worm—a scarlet feathery plume—extends into the frigid seawater just a few degrees above freezing. The rest of the white tube stands in water heated to about 70 degrees Fahrenheit.

"It's like having a 40-degree temperature difference between your 'head' and 'feet,'" Kang says. "I don't know any animal that does this."

Poison versus Food

The chemical brews gushing out of the vents provide nutrients for deep-sea life. One ingredient of the vent fluid—hydrogen sulfide, or rotten-egg gas—is toxic to most land-based life. But poison for one creature is food for another.

The tubeworms derive all their nutrients from bacteria that live in their gut. The bacteria use hydrogen sulfide as an energy source to produce carbohydrates for the worm.

Kang suspects that the worm bridges two temperature zones because the bacteria in its gut require warmth while its red plume harvests nutrients in the cooler water above.

Kang's sensor is helping to determine the tubeworms' chemical environment.

"Chemistry is everything to these animals," Shank says. Chemistry affects where species live, and for how long. The tubeworms are undersea pioneers—the first to colonize new vent sites; they were followed by mussels and clams.

The vents continually switch on and off, often abruptly halting the supply of nutrients. "This creates boom-and-bust communities," Shank says.

When the vents stop flowing, all the animals die. To survive these cycles, tubeworm larvae must sense the location of new vents, settle down, grow fast, and reproduce.

That complicates life for the scientists, too. So their next goal is to build sensors that can be left on the seafloor for long periods.

"Continuous monitoring is necessary," Kang says. "Otherwise, we just get snapshots, and we miss the relationships between the chemistry in the area and the species that live there."

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