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Planet Earth

Cave-Dwellers in Romania

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In 1986 engineers drilling an exploratory hole at a possible construction site in southeastern Romania, near the Black Sea, discovered a cave 80 feet below ground. Taking advantage of the chance find, explorers from the Emil Racovita Speleological Institute of Bucharest soon clambered down the hole. They were stunned by what they saw: the cave was crawling with spiders, scorpions, leeches, millipedes--a rich variety of invertebrate animals, all thriving in total darkness and isolation. One of the explorers, a biologist named Serban Sarbu, later became a refugee from his country’s political troubles. He went to work at the University of Cincinnati for a time before returning to Romania--and the cave--in 1990. Last June, Sarbu and his Cincinnati colleagues finally published a report that showed just how extraordinary the Romanian cave is. It is the first known ecosystem on land that doesn’t derive its energy from sunlight through photosynthesis.

The base of the food web, the researchers discovered, was a thick scum of bacteria floating on five feet of water at the bottom of the cave. The bacteria practice chemosynthesis: they use hydrogen sulfide in the cave air, rather than sunlight, as a source of energy to make carbohydrates. Sarbu and his colleagues found that all the animals in the cave either fed on the bacteria directly or ate animals that did. Hot springs on the ocean floor support much the same kind of food chain, and the source of the hydrogen sulfide in the cave is probably geothermal as well; the water is relatively warm. I would expect that these kinds of ecosystems are more widespread, says Brian Kinkle, a Cincinnati microbiologist. We just happened to stumble across this one.

The ecosystem is also an ancient one, having been sealed by some geologic event 5.5 million years ago. Since then the trapped animals have developed the typical appearance of many cave creatures, turning blind and pale and small. They’ve also evolved into a number of new species; 33 of the 40 or 50 species that now live in the cave are found nowhere else. Meanwhile the bacteria may have done more than provide food: they may have enlarged the habitat. The sulfuric acid they excrete gnaws away at the cave’s limestone walls much faster than water alone would.

Kinkle is confident that other caves like the Romanian one will turn up on Earth--and perhaps on other planets. When NASA sent the Viking probe to look for life on Mars, it looked only on the surface, even though there is evidence of underground water. Drilling down tens of meters might be a better strategy, says Kinkle. If there’s life, it would be underneath the surface; and if it’s underneath the surface, it’s not going to be photosynthetic.

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