The Ayalon Cave and it's Impact on the Cave Ecosystem

The Ayalon Cave and its Impact on the Cave Ecosystem

In 2006, the Ayalon Cave was discovered in the Ramle, Israel. An area, located between Jerusalem and Tel Aviv. The cave was first discovered and explored by Prof. Amos Frumkin of the Hebrew University of Jerusalem geography department and his coworkers, behind a small opening made by a bulldozer during quarrying by the local cement factory. The cave system behind the opening consists of chambers and tunnels reaching a total length of about 2.5 km, and includes a room 30 m high with a diameter of 40 to 50 m, with an underground lake. The cave system dates back millions of years, and extends to a depth of 100 m beneath the surface of the quarry. The cave's surface is situated under a layer of chalk that is impenetrable to water. The underground lake is part of the Yarkon-Taninim aquifer, one of Israel's two aquifers, yet it is different in temperature and chemical composition from the main waters of the aquifer. The lake's temperature and salinity indicates that its source is deep underground. Sulfide is present in the lower layers of the water.

It rapidly became clear that the cave system houses a unique ecosystem, which includes at least eight previously unknown, ancient animal species – crustaceans and other invertebrates resembling scorpions, that have evolved in continuous darkness in the cave since the caves had been sealed off from the outside world millions of years ago. The invertebrate animals found in the cave – four seawater and freshwater crustaceans and four terrestrial species have been discovered thus far – are related to but different from other, similar life forms known to scientists. These novel forms of animal life are presently being characterized and described. It is already clear that more unusual animal life forms occur in the caves, and the true biodiversity and the nature of the food web in the cave is now under investigation. Following the discovery of this unique ecosystem, quarrying at the site has been halted, and the area is closed to the public and is restricted to scientific research, with full cooperation from the Israel Water Commission and from Nesher Industries, to which the quarry belongs.

The discovery of such a diverse and well developed macrofauna at a site that does not receive any sunlight, and in which also no other obvious sources of available organic carbon are present, raises the question about the source of primary production on which these macrobiota make a living. As photosynthesis does not occur at the site, the obvious alternative is chemosynthetic production. Sulfide is present in the anaerobic waters below the oxidized surface layer, and it is therefore more than probable that oxidation of sulfide by chemoautotrophic sulfur bacteria produces the organic carbon that presents the basic food source for the animal life in the cave. Microscopic examination of material suspended in the water in the cave showed dense accumulation of filamentous bacteria resembling Beggiatoa, filled with elemental sulfur (an intermediate in the oxidation of sulfide to sulfate by this bacterium).

The Ayalon Cave is not the first case of the discovery of a "sunlight-independent" ecosystem. Well-known examples are the habitats around deep-sea hydrothermal vents found at spreading centers at several 2-3 km deep sites at the bottom of the oceans. Complex ecosystems with unusual tube worms, clams, and other macroanimals develop there, all based on carbon produced by (in part symbiotic) sulfur oxidizing and methanotrophic bacteria that oxidize sulfide and methane expelled from the seafloor by volcanic activity. The first case of an underground cave in which the animal life may depend on chemoautotrophic bacterial production was reported with the discovery of the ecosystem of Movile Cave, Romania, in the early 1990s (Lascu et al., 1993; Sarbu and Kane, 1995; Sarbu et al., 1994a, 1994b, 1996). There are only few similar cave systems worldwide in which the importance of chemoautotrophic sulfur bacteria is so pronounced, and such caves are thus perfect model systems for the study of chemoautotrophic primary production. It is already clear that the Ayalon Cave presents us with such a model system. The finding of extensive growth of Beggiatoa-type colorless filamentous sulfur bacteria in the cave strengthens this assumption. The present (pre)proposal to GIF aims at the characterization of the community of chemoautotrophic sulfur bacteria and its importance to the unique cave ecosystem.