The subterranean world is an unexplored, under researched frontier that we tend to regard as an empty place. Further exploration, although fragmentary, has revealed that a diverse range of fauna live underground.
The animals that live in aquifers, underwater pools and caves are called stygofauna. They inhabit a wide variety of groundwater environments – in both fresh and saline water, located in rock, clay, gravel, karst, sediment, fissures, cracks and caves. Stygofauna are found in all states of Australia, but appear particularly diverse in the desert regions where the underground water provides a refuge from the arid conditions on the surface above.
Stygofauna mainly consist of crustaceans, syncarids, snails, worms, diving beetles, mites, insects and fish. They are highly adapted to their localised niche within an aquifer. Commonly their adaptations are a lack of eyes, pale pigmentation, slow metabolism to cope with food shortages and long antennae and legs to provide sensory information in their pitch black world.
Australian stygofauna are closely related to stygofauna species in other continents. This indicates that these stygofauna species originally had a common ancestor in the ancient continents of Gondwana and Pangeae, and that the groundwater and its inhabitants were present before the ancient super continents split apart.
The vertebrate stygofauna are fish, two species that have been identified are the blind gudgeon and the blind cave eel. The blind cave eel is the world's longest cave fish, it is pure white and eyeless and may grow 40 cm. The blind gudgeon has been found in fresh and salt water at depths of 68 metres below the surface at water temperatures of 30 degrees C. They move widely through the water column, and adapt to the remarkable range of chemical and physical characteristics that exist in different water masses. They hunt other stygofauna and terrestrial insects accidentally introduced into the aquatic system. Very little is known of the biology and reproduction of either species. In view of the limited studies of stygofauna fish, there may be other species. There is anecdotal evidence of fish which could only have originated from underground aquatic systems swimming near the surface of deep bores.
Human pressure is threatening this newly discovered biodiversity through uncontrolled groundwater use, excavation, pollution and by contamination.
Stygofauna are very under researched but it is believed that they may have an important function in regulating and maintaining aquifers by preventing subsidence, bioremediation of waste, nutrient cycling and improving underground water quality. Our knowledge of these functional relationships is almost nonexistent and some scientists warn that we may only discover their significance as problems arise when groundwater biodiversity declines or disappears.