Albuquerque, New Mexico--Marine biologist Charles Fisher has solved a mystery of the deep: How do some giant tube worms that live on the ocean floor obtain the hydrogen sulfide they need to survive? The answer: They mine it.
Hydrogen sulfide is an essential nutrient for bacteria that live in the guts of the meter-long tube worms, in a symbiotic relationship with their hosts. The microbes process sulfide and inorganic carbon, releasing carbohydrates that nourish the worm. Tube worms that live around volcanic vents on the deep sea floor have a plentiful supply of hydrogen sulfide dissolved in the hot water that spurts from the vents. But tube worms living elsewhere on the ocean floor have no obvious source of this nutrient.
Fisher, a researcher at Pennsylvania State University, has spent several years trying to explain this conundrum. He looked for hydrogen sulfide in ordinary seawater near tube worms living 600 meters beneath the surface of the Gulf of Mexico, but couldn't find enough of the gas to keep the creatures alive. So he descended in a submersible, collected tube worms together with the rock they were attached to, and found the answer.
At the annual meeting of the Society for Integrative and Comparative Biology here last week, Fisher reported that the tube worms had sprouted transparent, flexible tubes through and around the rock. Vent-dwelling tube worms lack these appendages. Laboratory tests indicated that these "roots" can absorb hydrogen sulfide dissolved in the surrounding sediment, Fisher said. But he has not yet determined exactly how they extract the nutrient, he noted.
Fisher has also been measuring the growth rates of these tube worms and found that they grow much more slowly than those living around vents. Large, slow-growing worms, he said at the meeting, may be at least a century old.
Fisher's findings "are pretty novel," says marine biologist Peter Girguis of University of California, Santa Barbara. Girguis says, however, that Fisher's estimate of the worms' longevity still needs to be confirmed.