A species of worm that thrives on undersea hot-water vents prefers the hottest water possible, choosing to live at temperatures that kill other animals, researchers reported Thursday.
Their ability to withstand hot water shooting like a geyser from hydrothermal openings may help the stalklike worms prey on bacteria that other animals cannot reach, the researchers report in Friday's issue of the journal Science.
The tiny worms, known scientifically as Paralvinella sulfincola, chose water heated to 122 degrees Fahrenheit (50 degrees Celsius) and made brief forays into water as hot as 131 degrees F (55 degrees C), Peter Girguis of Harvard University and Raymond Lee of Washington State University reported.
"To our knowledge, every other vent organism down there dies at temperatures way below 50 and 55" Celsius, Girguis said in a telephone interview.
The worms live on underwater vents found at depths of 1.4 miles (2,200 meters) off the coast of Washington state. They are studied and collected using deep-sea submersible vehicles.
They belong to a group known as polychaetes and build tubes made out of mucus but can move around freely. They resemble tiny red palm trees, with frond-like red gills.
Many different animals live on the undersea vents, not merely tolerating the sulfur, heat and pressure, but thriving in it. They eat the bacteria that can live in much higher temperatures than more complex animals.
From boiling to near freezing
The water pours out of the vents at temperatures far above the boiling point, but it quickly cools in the chilly sea water. Because of the conditions, it is difficult to know precisely which temperatures the animals can tolerate. So Girguis and Lee set up a unique experiment.
"We wanted to see what temperatures the worms preferred and what temperatures they could survive," Girguis said.
They built a special pressurized aquarium, with a heating element on one end and a cooling element on the other.
This created a thermal gradient — with water ranging in temperature from 68 degrees F (20 degrees C) to 142 degrees F (61 degrees C). They threw the worms in.
"What happened really kind of shocked us, which is they all very quickly moved when we imposed the thermal gradient," Girguis said.
"They just picked up and went," he added. "It was like they were having a little conference" in the hotter water.
The worms survived for as long as seven hours at 122 degrees F (50 degrees C), and would spend as long as 15 minutes at 131 degrees F (55 degrees C). Water of 140 degrees F (60 degrees C) killed them.
How much heat can other animals take?
These temperatures are far hotter than anything most animals can survive. Other researchers have found that desert fire ants die at 131 degrees F (55 degrees C). In comparison, the temperatures in a hot tub range from 100 to 105 degrees F (38-40 C).
Desert air is often hotter, but water conducts heat much more efficiently than air does.
Girguis said the experiment answered a key question about the physiology of the worms.
The cells of complex animals all rely on structures called mitochondria, which provide power to the cells. Mitochondria start to break down at temperatures of 122 to 131 F (50 to 55 degrees C), Girguis said. The worms may skate on the borderlines of this limit but do not break it.
They almost certainly have multiple other adaptations, he said, including heat-tolerant enzymes in their cells.