Live long and prosper.

Hydrothermal vents, those fissures where hot, mineral-laden water spews into the cold sea, aren't the only places on the ocean floor that host a surprising bounty of life. Many of the unusual life-forms spotted there- clams, tubeworms, mussels, and crabs, for example-also reside at ocean seeps, sites where methane, oil, and other fluids ooze out of the sediment and into the surrounding water (SN: 9/27/86, p. 198). Yet tubeworms at seeps pursue a far different lifestyle from that of similar worms at vents, says Charles Fisher of Pennsylvania State University in State College.

Tubeworms, notes Fisher, are "basically a big bag of bacteria stuck inside an animal." The worms, which provide a safe haven for the bacteria, derive all of their energy from the microorganisms, he explains. At vents, these bacteria live off hydrogen sulfide in the hot plume. By diving to hydrothermal vents, Richard A. Lutz of Rutgers University in New Brunswick, N.J., and his coworkers have found that tubeworms can grow so rapidly-almost a meter a year-they may be the fastest-growing of all marine invertebrates. "They live hard, live fast, and die young," jokes Fisher.

Fisher and his colleagues monitor tubeworm growth with an instrument they nicknamed "the hair dryer." They place the device, which resembles the large hair dryers used in salons, over a group of tubeworms and signal it to release a permanent dye. When the investigators return to the site a year later, they gauge how much the tubeworms grew by measuring the creatures' undyed tips. While hydrothermal vents are usually short-lived, often lasting only a year or two, ocean seeps last longer and may offer a more stable environment, says Fisher. Perhaps not surprisingly, then, his group has found that the tips of seep tubeworms in the Gulf of Mexico advance by less than a centimeter a year.

"They grow incredibly slowly," says Fisher, who estimates that seep tubeworms live a century or more.

Seep tubeworms also differ from their vent counterparts in that they develop rootlike extensions up to half a meter long, says Fisher, who notes that most sulfur-containing compounds at seeps are not found in the water but in the sediment. "We're postulating that [the tubeworms] are using their roots to mine sulfides from the sediment. They are animals that live a very full life with deep roots," laughs Fisher.