An algae - Desert snail food chain: Energy flow and soil turnover.

Abstract

The feeding ecology of adult desert snails (Sphincterochila zonata), inhabiting a loess plain in the Negev Desert, was studied during a 7-year period. Energy flow and soil turnover determinations were made at the individual and population level on the basis of field observations and data derived from laboratory simulations. Sphincterochila zonata were only active on 8-27 winter days annually, otherwise they were dormant. The snails fed exclusively on algae that grew on the soil surface following rain. The mean annual dry-weight biomass of algae was 197.4(±118.1) gr·m-2. The dry weight biomass of snails ranged from 0.02-0.14 gr·m-2. Annual production in the food chain varied substantially from year to year (1-1539 Kj·m-2), but the net annual energy balance of the snails was always positive. Soil crust turnover, resulting from grazing of snails on algae, was estimated at 142 kg·hectare-1 during the study period.The annual magnitude of energy flow and soil turnover is determined by the soil surface moisture regime which in turn, is a function of rainfall patterns. Sphincterochila zonata may serve an important role in Negev ecosystems by dispersing soil algae and altering soil structure. The snails are not subject to substanding predation by rodents but may occasionally serve as an important food source for migrating birds.