How do tube worms on the bottom of the ocean live without light?
(Lansing State Journal, October 22, 1997)
The water springing from the vents is rich in hydrogen sulfide, the same compound which gives rotten eggs their distinctive odor. Although not a very attractive source of food, some tiny free-living bacteria located near the vents think otherwise. In a process akin to the way in which green plants use the power of sunlight for photosynthesis, these bacteria utilize the hydrogen sulfide emitted from the vent as a source of energy to convert carbon dioxide from the surrounding sea water into sugars that they need for growth.
The hydrothermal vents are also inhabited by bizarre creatures which appear like thick-stemmed tulips up to 3 meters long with bright red plumes. These tube worms, Riftia pachyptila, have no mouth or gut. Instead, their red plume rimmed with blood vessels reaches into the vent waters. Oxygen, carbon dioxide and hydrogen sulfide bind to carrier molecules in the blood. As the heart pumps, these three compounds are delivered to a very specialized tissue which contains densely packed bacteria. In return for a stable environment in which to live, the bacteria provide Riftia with all the organic compounds required for growth. The association of two different living entities is called symbiosis. In this instance, it can be said that the tube worms provide housing, and the bacteria pay rent.