Thriving colonies of undersea life, including three-foot-long tubeworms, limpets, mussels and clams, have been found on the floor of the Gulf of Mexico at vents where petroleum seeps out of natural underwater reservoirs, scientists reported Tuesday at an American Chemical Society meeting in New Orleans.
The organisms are very similar to those found at deep-ocean hydrothermal vents in the Pacific Ocean and at other underwater sites. The apparent ubiquity of these unusual organisms--which depend on chemicals rather than sunlight for energy--suggests that they may play a larger role in global ecology than had previously been thought.
"Instead of hindering the population of organisms on the sea floor, it appears that the oil seepage actually enhances it," said oceanographer Mahlon C. Kennicutt II of Texas A&M University's Geochemical and Environmental Research Group in College Station.
Kennicutt is not the first to find such organisms in the gulf. Biologist Barbara Hecker of Columbia University's Lamont-Doherty Geological Observatory in Palisades, N.Y., had observed some of the same organisms in 1984, but could not determine what they were using for an energy source. Kennicutt and marine biologist James Childress of the University of California, Santa Barbara, had also netted some of them from trawlers, but did not know their origin.
Earlier this year, however, Kennicutt made two dives about 150 miles off the Louisiana coast in the Johnson Sealink submersible and one in the U.S. Navy's experimental NR-1 submersible. A large new oil field is expected to be developed in that region in the next five to 10 years, Kennicutt said. And, with partial funding from the petroleum industry, he was looking for oil seepage as an indicator of good sites for drilling.
In the 2,000-foot-deep water, he found the seepage sites and, surrounding them, the unusual life. "It really surprised me because everyone had always thought the hydrocarbons in the oil would (kill off) most marine life," he said in a telephone interview. "But these were thriving quite well."
Kennicutt also found that the seeps release large amounts of oil. By analyzing the proportions of different components of the oil--in effect, producing a chemical fingerprint--he was also able to show that most of the oil polluting the gulf comes from the seeps rather than from human activities.
And even if additional oil and gas do find their way into the gulf waters, he added, it may not have a deleterious effect because the local ecology has already evolved to cope with a naturally polluted environment.
Not all biologists would agree with that conclusion, but most would agree that the new discoveries are changing our ideas about the fundamental nature of life.
Scientists once thought that all life on earth depended on energy from the sun to fuel its biochemical processes. Algae and other plants collect this sunlight and convert it into sugars and other chemicals that are consumed by insects and animals, which are in turn eaten by other animals, including man, higher up the food chain.
In 1969, however, fishermen working off the Northern California coast netted the first tubeworm, an unusual form of life that had no mouth and no gut. Scientists ultimately discovered that the tubeworms were filled with bacteria that could live on hydrogen sulfide--a noxious gas that, to most organisms, is more toxic than cyanide. The tubeworms appear to "harvest" the bacteria periodically to furnish energy and other chemicals they need to grow, said marine biologist Meredith Jones of the Smithsonian Institution in Washington.
In 1981, researchers found the first vents--as much as two miles below the ocean's surface--where hot water rich in hydrogen sulfide and methane gas boils up from underground. These vents were surrounded by huge biological communities. All the different species ultimately depended on bacteria that live on either hydrogen sulfide or methane.
"The fact that these colonies grow to such large sizes and support so many different organisms without energy from sunlight is overwhelming to biologists," Jones said. Scientists are just now beginning to understand their life processes, but many questions remain, he said, including how they reproduce and how they get from one vent to another.