Cave of the Sulfer Eaters

Article excerpt

Unassisted by solar energy or green plants, a complex food web has evolved in Cueva de Villa Luz in total darkness.

"Mother, Father, may we enter your cave and take from its bounty?"

Every spring, at the end of the dry season in the southeastern Mexican state of Tabasco, a group of whiteclad Soque elders-descendants of the Maya-perform the ceremony they call La Pesca de la Sardina (Harvesting of the Sardines) at the entrance to Cueva de Villa Luz, a sulfur-spring cave at the edge of the Chiapas highlands. Chanting in a Mayan language and witnessed by residents of the nearby town of Tapijulapa, the men ask the cave's guardian spirits to allow them to enter and harvest the small, pale pink cave fish-a special gift from their gods to sustain them until the rains bring new crops.

After the ceremony, about a thousand men, women, and children-equipped with torches, candles, and flashlights-enter the large front section of the cave, temporarily illuminating a subterranean world whose creatures are accustomed to total darkness. The harvesters scatter a powder made from the root of the barbasco vine into the milky white stream; the root's natural pesticide interferes with the fishes' respiration, and they rise, gasping, to the surface. Although thousands of pounds of fish are taken, enough remain (and recover from the toxin) to replenish the population the following year.

Cueva de Villa Luz's fish are linked to an unusual and extensive food web whose members depend for energy not on photosynthesis from sunlight but on an inorganic chemical process: the oxidation of sulfur compounds. When veteran cave explorer James Pisarowicz first entered Cueva de Villa Luz in 1987, he was struck by its strange geochemical features-the ubiquitous yellow sulfur, clear gypsum crystals, and multicolored slimes coating the walls. The "rotten egg" odor of hydrogen sulfide pervaded the air. Hanging from the ceilings were strange rubbery deposits that dripped sulfuric acid-massive colonies of sulfuroxidizing microorganisms. They looked like stalactites made of mucus, so Pisarowicz dubbed them snottites.

When he returned with a surveying crew the following year, Pisarowvicz had difficulty keeping them in the cave. "This is the first time I had ever been in a cave where the survey crew mutinied because they were being burned by acid," he wrote in his 1988 report. Burned flesh, pitted carbide lamps, and disintegrating clothes made his colleagues understandably skittish about remaining in the cave. But potential revelations about new life forms repeatedly lured Pisarowvicz back, and in 1996 he invited me to join a reconnaissance expedition.

Despite decades of experience as a cave geologist and explorer, I was unprepared for Villa Luz. Most caves are carved out by carbonic acid, the compound that forms when rainwater and melting snow pick up carbon dioxide from the air and soil. Slowly this acidthe same mild acid we drink in soda pop-trickles into cracks in the limestone and, over long periods of time, eats away the rock. I was aware that recent explorations in New Mexico's Carlsbad Caverns National Park had revealed caves with very different kinds of geochemical histories. One type seems to have been at least partially carved out by chemical reactions in the sulfur-rich water that rises from beneath the ground. Villa Luz quickly taught me that sulfur-based caves are not formed solely by inorganic chemical processes, however; they are also shaped by the densely concentrated microbial life forms they harbor. These bacteriawhich derive all their energy from inorganic chemical reactions-metabolize the hydrogen sulfide in the water and the oxygen in the cave's air to produce sulfuric acid, the same acid used in car batteries.

The sulfuric acid then reacts with the adjacent floor or wall, but rather than completely dissolving the rock, it converts the limestone (calcium carbonate) bedrock into gypsum (calcium sulfate). …