Beneath the arid landscape of outback Western Australia is a world of wonderful creatures.
Stygofauna (animals that live in underground pools) have been living secretly in arid areas of Australia for millions of years. Until recently no one even knew they existed, but now these amazing creatures are being studied and their secrets uncovered.
Subterranean amphipods. Image: Bill Humphreys, WA Museum
The desert land of the Yilgarn Region in central Western Australia is home to an extraordinary ecosystem of subterranean water animals known as stygofauna. Scattered throughout the region are hundreds of limestone deposits (calcretes), each containing a honeycomb of holes and crevices filled with water.
Map of the Yilgarn region in WA. New Scientist image: www.newscientist.com
Over millions of years these calcrete aquifers have evolved a variety of unique animal species adapted to living underground, including blind water beetles and a variety of crustaceans, such as shrimp-like amphipods and isopods.
The honeycomb structure of calcrete
Once considered the least likely place on Earth to find stygofauna, Australia is now considered a world hotspot for them, with biologists at the South Australian and Western Australian Museums and the University of Adelaide leading the way in describing the enormous diversity of species present.
Illustration: Alex Green, UK
More of Alex Green's work can be seen here
Underground Surprises
How was the stygofauna discovered?
The hot dry desert region of central WA is not the most likely place to find animals adapted to living in water, which is probably why the fauna remained undiscovered until the late 1990s.
The arid landscape of the Yilgarn Region
Bill Humphreys (left) and Chris Watts (right) fishing for stygofauna at a pastoral well
Dr Bill Humphreys from the Western Australian Museum had been finding amazing new species of stygofauna in limestone (calcrete) aquifers in the Cape Range and Pilbara regions of Western Australia. He suspected that animals might be found in the numerous other calcrete aquifers scattered through the Yilgarn region of central WA. He employed Stefan Eberhard, a local cave enthusiast, to find out by dropping a plankton haul net down a few wells and bore holes on Paroo Station. On the 24th of June, 1998, Stefan discovered what was to be the first species of an extraordinary new ecosystem.
Species of Stygofauna and Their Adaptions to Life Underground
The calcrete aquifers are home to the world's most diverse assemblage of subterranean water beetle species, with more than 100 species now described.
An extraordinary diversity of subterranean water beetles and two related surface species (top left with dark pigment). Image: Chris Watts, SA Museum
The diving beetles that live underground are related to those that live above ground. However the surface diving beetle species are dark in pigment and have eyes and wings to aid their dispersal. The underground species lost their eyes and wings and dark pigment and are now a golden translucent colour. At the same time they have evolved other characteristics to adapt to life underground, including a slower metabolism, with no need to continually come to the surface of the water to obtain oxygen, and an ability to survive long periods without food. They have longer life spans and an enhanced ability to crawl through crevices compared to their surface relatives, that are adapted for rapid diving and swimming. Their lack of wings and eyes means that they are no longer able to disperse through the air like their surface ancestors, and are now confined within a single isolated calcrete body, that is equivalent to an "island under the desert".
Subterranean amphipods. Image: Bill Humphreys, WA Museum
The desert land of the Yilgarn Region in central Western Australia is home to an extraordinary ecosystem of subterranean water animals known as stygofauna. Scattered throughout the region are hundreds of limestone deposits (calcretes), each containing a honeycomb of holes and crevices filled with water.
A new species of the isopod Haloniscus from Jimmy's Well, Carnegie, WA. Iimage: Stefano Taiti, Italy
There are also a variety of different crustacean species, including numerous shrimp-like amphipods, isopods of the genus Haloniscus, worm-like bathynellids and tiny copepods. These species also lack eyes and pigment, and have evolved new characteristics such as longer antennae for detecting food in the dark and flattened bodies for moving through crevices.
How did the stygofauna evolve?
Most of the species found in calcrete aquifers are closely related to species also found in surface water. For example, the subterranean water beetles are related to a number of surface species that were once widespread through the Yilgarn Region, at a time when river systems and fresh water lakes were a common feature of the landscape, some 30-10 million years ago. A dramatic change in the climate (10-5 million years ago) led to the drying of surface water and the lowering of the water table so that the only permanent sources of water in the region were in the ground. Animals, once adapted to living on the surface, followed the water table down and were able to avoid extinction by evolving new adaptations to living underground within the holes and crevices of calcrete.
Illustration: Alex Green, UK
Each isolated calcrete body appears to have evolved its own unique suite of species, suggesting that individual calcretes are equivalent to "islands under the desert".
With more than 200 major isolated calcrete bodies in the region and thousands of smaller deposits the diversity of stygofauna in the Yilgarn is likely to be enormous, yet scientists have only just scratched the surface in describing this extraordinary diversity.
Fishing in the Desert: A Typical Expedition
Remko Leijs fishing for stygofauna. Image: Bill Humphreys
Most of the calcrete aquifers are found on remote pastoral properties or mining lands in the Yilgarn region, about a day's drive north-east of Perth. There are few bitumen roads in the region and only the occasional town, so expeditions require the use of well equipped 4WD vehicles.
The stygofauna are captured in plankton nets that are hauled through the water of bore holes and wells in the calcrete, so a major task of an expedition is to search the landscape for these holes.
Chris Watts sorting stygofauna in the mobile lab. Image: Steve Cooper
We usually take a camper trailer, so that we can travel the countryside with freedom and pitch camp as soon as the sun sets. The tent of the trailer is also used as a laboratory for sorting the day's live catch of stygofauna under microscope.
Flood in the Yilgarn Region. Image: Remko Leijs
The weather can be all extremes in the Yilgarn region, ranging from very hot during the day to freezing cold at night. It is usually very dry, but occasionally some major storms sweep across the landscape and roads, once dry and dusty, can turn into slippery mud and be prone to major flooding. Getting bogged or spiking a tyre with a sharp branch or root of a mulga tree is a common occurrence when driving along the rough farm tracks in search of a pastoral well or bore hole. Your city life is left far behind in this remote landscape as you focus on the basics of life and the excitement of a new stygofauna discovery.
DNA Analyses
We use DNA sequence data to test for the existence of new species and investigate their evolutionary origins and relationships with other species. One of our main target genes for our study is the cytochrome oxidase subunit 1 gene, which is found in the DNA of mitochondria, located in the cytoplasm of all animal cells. In order to study this gene we need to generate millions of copies of it, so that we can use techniques to directly read off its DNA sequence. The method that we use is called the polymerase chain reaction or PCR, a wonderful technique invented by Kary B. Mullis in 1985.
Polymerase Chain Reaction: details of the method
Management and Conservation Issues
Mine in the Yilgarn Region
Much of the water in calcretes is used in the pastoral industry or as a source of water for mining activities. Calcrete itself is also utilised in mining operations to neutralise acid or for road building. Overuse of groundwater may lead to the lowering of the water table below the level of the calcrete, which may cause extinction of all the fauna within it.
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