Snails Dine at Desert Dust Depot
Hartley, Karen, Science News
Snails dine at desert dust depot
Winds from the Arabian and Sinaipeninsulas sweep across the limestone rocks of Negev Desert Highlands in Israel, depositing dust in their wake. Long considered a major source of soil formation in the Negev, these winds apparently are not the only significant contributors. Researchers are finding that in the sands below, two species of snails may be equally responsible for soil formation.
Although plant-eating animals havebeen known to affect their ecosystems through overconsumption of a resource, such as overgrazing, these snails have a significant regulatory impact despite the small amount they consume, according to a report in the May 29 SCIENCE by Clive G. Jones of the Institute of Ecosystem Studies in Millbrook, N.Y., and Moshe Shachak and Yigal Granot of the Mitrani Center for Desert Ecology in Israel.
The two species, Euchondrus albulusMousson and Euchondrus desertorum Roch, are found throughout the desert at a rate of 21 snails per square meter and feed seven months out of a year during seasonal dew formation. The lichens they feed on, known for their toughness and low digestibility, grow under the rock surface at depths between 1 to 7 millimeters. Called endolithic lichens, they are cryptogams that don't bear seeds or flowers, and are dominant in limestone in extreme environments. The arid desert terrain these hardy lichens and snails call home is a hilly region some 5,000 square miles large and covered mostly by rock.
Videotapes of lab experiments showedthe snails foraging in short side-to-side motions for about 20 minutes, leaving behind a white trail in the process. Depths of the trails varied, say the researchers, possibly because the snails might rebrowse trails for the lichen that grew there within 48 hours of when they made their first feeding pass. …