Water pouring out of vents can reach temperatures up to about 400 C; the high pressure keeps the water from boiling. However, the intense heat is limited to a small area. Within less than an inch of the vent opening, the water temperature drops to 2 C, the ambient temperature of deep seawater. Most of the creatures that congregate around vents live at temperatures just above freezing. Thus chemicals are the key to vent life, not heat.
The most prevalent chemical dissolved in vent water is hydrogen sulfide, which smells like rotten eggs. This chemical is produced when seawater reacts with sulfate in the rocks below the ocean floor. Vent bacteria use hydrogen sulfide as their energy source instead of sunlight. The bacteria in turn sustain larger organisms in the vent community.
The clams, mussels, tube worms, and other creatures at the vent have a symbiotic relationship with bacteria. The giant tube worms, for example, have no digestive system-no mouth or gut. The worm depends virtually solely on the bacteria for its nutrition, says microbial ecologist Colleen M. Cavanaugh of Harvard University. Both partners benefit.
The brown, spongy tissue filling the inside of a tube worm is packed with bacteria-about 285 billion bacteria per ounce of tissue. Its essentially a bacterial culture, says Cavanaugh.
The plumes at the top of the worms body are red because they are filled with blood, which contains hemoglobin that binds hydrogen sulfide and transports it to the bacteria housed inside the worm. In return the bacteria oxidize the hydrogen sulfide and convert carbon dioxide into carbon compounds that nourish the worm.
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