Most of us visualise fish swimming in rivers when we think of aquatic fauna. However, an unusual array of aquatic animals also live underground*. Just as we are starting to discover these creatures, threats to their existence mount.
There are several types of subterranean aquatic systems. They include different types of aquifer, water bodies associated with caves in limestone (karst) landscapes and even subterranean estuaries (anchialines). All can potentially support life.
The animals that live in these lightless environments are called stygofauna. Stygofauna consist predominantly of different types of crustaceans. These are the pale and generally diminutive cousins of the more familiar yabby and prawn. Their otherworldliness is matched by sci-fi names like isopod and amphipod.
Other invertebrates (creatures without backbones) such as worms, snails, and beetles are also found and even two species of blind fish.
It is likely that much of our stygofauna remains un-documented*. Surveys in new areas tend to unearth new species such as in the Pilbara region (Western Australia). There, a new genus of isopod and over 110 species of ostracod have been discovered. In addition, a high diversity of dytiscid diving beetles are the remnants of multiple independent colonisations of aquifers that subsequently became subterranean ‘islands’ isolated by the onset of aridity.
In fact one of the features of stygofauna is their high endemism (species confined to a particular region). This is because their habitats are often fragmented meaning they can’t move long distances.
While subterranean aquatic systems are often separated from each other they are connected with surface water systems such as streams. In dark environments without plants, most subterranean foodwebs rely on water percolating down from the surface to supply food (organic matter) and dissolved oxygen.
We are only beginning to understand what services these unseen systems are providing us on the surface. They support a diverse and often ancient array of fauna and can be a source of water. Studies also suggest groundwater ecosystems can break down contaminants (bioremediation), process nutrients that feed back into streams and streamside vegetation, and mitigate floods and erosion through absorbing water.
As surface waters deteriorate in quality and quantity there are increasing demands on groundwater. The rate of use can exceed the rate it is replenished for some time before the impacts of extraction on ecosystem services become apparent. Ironically more information about stygofauna is “coming to light” through impact assessments associated with mining proposals.
A better understanding of how these systems work is required if we are to understand what we may be losing and to effectively manage surface and groundwater together.
* The full article on which this piece is based is: Ecology and management of subsurface groundwater dependent ecosystems in Australia – a review. By: M. Tomlinson and A.J. Boulton. Marine and Freshwater Research, 2010, 61, 936–949