It is a scene straight out of a horror film set in Transylvania: isolated from the world for millions of years, an underground cave in Romania, shrouded in darkness, is crawling with unique life forms.
Entirely new species, ranging from bacteria to blind spiders, leeches and water scorpions, which have been cut off from the rest of the world for about 5 million years, have been discovered in the Movile Cave, in Dobrogea, west of the Black Sea, near the Casimcea Valley.
The cave, found by accident during construction work in 1986, contains at least 31 species new to science and a food chain that does not depend on the energy of the sun, but on energy from chemicals in the sulphurous ground water.
It is the first known subterranean ecosystem depending on chemistry rather than sunlight, Serban Sarbu, a biologist from the University of Cincinnati, told the American Association for the Advancement of Science in Baltimore.
On the earth's surface and in all but deepest parts of the ocean, creatures depend on sunlight to survive. If they do not harness sunlight directly, as with plants, they do so indirectly, by eating plants or plant-eaters.
The ecosystem is entirely different in the Movile Cave. In the darkness, "all the food is being produced inside the cave, using the energy that results from the oxidation of hydrogen sulphide", Dr Sarbu said.
The cave differs from others in important ways: its waters are much warmer than those of typical limestone caves, and are rich in the hydrogen sulphide that is apparently used to produce energy.
It is even possible that creatures in the cave are expanding their environment, by dissolving the limestone rocks and so enlarging the cave system.
At the bottom of the food chain are dense mats of microbes on the cave walls and the surface of the subterranean lakes. These use hydrogen sulphide to live, and produce sulphuric acid, which attacks the limestone and carves out more passages. The microbes are then eaten by creatures higher up the food chain, which so far appears to be occupied by spiders and leeches.
These are presumably the descendants of creatures trapped during the formation of the caves, when the Black Sea's level dropped dramatically about 5.5 million years ago.
In a pattern called troglomorphy, all the creatures in the cave show a reduction or loss of eyes and pigmentation, and enlargement of appendages and what scientists call extra-optic sensory structures, "antennae" of giant proportions.
One type of spider is born with the regulation eight eyes, but they all degenerate as it matures, so that it is blind by the time it becomes adult.
Although now at the University of Cincinnati, Dr Sarbu is from Romania. He started to explore the cave before 1990, but had to flee because of the oppression of Nicolae Ceausescu's regime. Only last summer was a team from the university able to restart explorations.
Dr Sarbu described their first findings yesterday. Researchers have proved that there are no links between the outside world and the cave's hidden galleries and air bells.
Sediment in the cave is devoid of cesium radionuclides, which is significant because surface sediments in Dobrogea contain high levels of these nuclides, owing to the 1986 Chernobyl accident.
The team developed fluorescent antibodies that bind only with certain strains of bacteria, and used them in the cave samples to see how abundant the bacteria were.
The environment is so fragile that only three people are allowed in at any time. The researchers also change clothes on entering the cave, to avoid bringing in "foreign" microbes.
"The ecosystem is the important thing, not the cave itself," Dr Sarbu said.
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