Root mats in ground water: a fauna-rich cave habitat

An unusually rich cave fauna of 41 species is reported from a 20-m stretch of a shallow groundwater stream in Western Australia. Epigean waters do not occur upstream of the cave and, downstream, cave waters emerge at the surface after flowing about 100 m through a system of limestone caverns and collapses. Most of the aquatic cavernicoles collected from the cave stream, therefore, appear to be confined to the subterranean realm. Potential food sources for the aquatic fauna of the cave were investigated. Inputs of dissolved organic matter, surface debris, cadavers, and guano into the cave stream were lacking or too small to provide sufficient energy for the abundant aquatic cavernicoles. Aquatic root mats were shown to be the only substantial source of food available. They belong to the native tree Eucalyptus gomphocephala and consist of fine, highly branched, feeder rootlets growing in mycorrhizal association with fungi. Most of the animals, both in terms of density and species number, also occur in the submerged root mats. At least some of the aquatic cavernicoles graze directly on the living rootlets, some feed on root mat detritus, and others are predatory. We propose that tree roots provide an important source of energy for subterranean fauna in shallow groundwaters both in Australia and elsewhere.