Collecting in the Dark Zone

Article | Updated 2 months ago

Photo of a man climbing out of a hole taken during a subterranean biology field trip.

Photo taken during a subterranean biology field trip.
WA Museum

Beneath our feet lies a hotspot of subterranean biodiversity. The Terrestrial Zoology Department perform research on the ecology, biology and taxonomy of Australian subterranean organisms. Over the last few decades, a substantial number of new species discovered by the research team has contributed to increase our knowledge of the State’s biodiversity. However, this underground fauna lives in hidden habitats, often inaccessible for sampling.

Which methods do scientists employ to collect this fauna in the field?

Abseiling, crawling, diving

Subterranean environments come in many different shapes and sizes but the most obvious type in Australia is caves. Caves are underground voids mostly formed by water dissolving soluble rocks like limestone, which form interconnecting voids that can be colonised by animals, mostly invertebrates, which are adapted to underground life. To discover these habitats, cavers sometimes have to go on very long walks in challenging terrain. When a cave is identified, researchers organise an expedition on the field, bringing with them a mobile laboratory to perform the first analyses. Caves are often big enough for a human to crawl through or walk into and some are so deep that scientists need to abseil to get into them.

Image of a person abseiling in a cave

Abseiling; photo taken during a subterranean biology field trip.
Image copyright WA Museum 

Image of people looking around inside a cave

Into the cave; photo taken during a subterranean biology field trip.
Image copyright WA Museum 

Image of a person sitting at a table using laboratory equipment outside

Mobile laboratory; photo taken during a subterranean biology field trip
Image copyright WA Museum 

Photo of a man climbing out of a hole taken during a subterranean biology field

Photo taken during a subterranean biology field trip.
Image copyright WA Museum 

To collect the fauna, researchers seek the more humid parts and where roots, plant debris, or guano from bats or birds provide a food source. In the case of underwater habitats like the Bundera Sinkhole, the only way to observe subterranean life is to dive into the cave’s depths. Scientists wear very specific equipment, including a closed circuit breathing apparatus to prevent bubbles forming, which would upset the chemical balance in these fragile ecosystems.

A diver sitting at the surface of the water

A diver with a closed circuit breathing apparatus to prevent bubbles forming which would upset chemical balance in fragile ecosystems.
Image copyright WA Museum 

Digging, feeding, waiting

Most voids are so small that a human cannot enter, or else have no opening at the surface. To study the subterranean fauna living in these voids, scientists examine boreholes that have been drilled for mineral exploration or for water. A small container of sterilised dry leaf litter is dropped down into the borehole using a piece of fishing line and left for several months. When scientists return to pick it up, the litter has been colonised both by underground organisms feeding on leaves and predators. The collection is placed into a plastic bag, kept cool and sent to the Museum for further analyses. 

Man digging out a borehole

Dr Bill Humphreys, curator in subterranean biology at the WA Museum, digging out a borehole that has been covered up in the past.
Image copyright WA Museum 

Man crouched beside a borehole

Dr Bill Humphreys preparing a small container of sterilised dry leaf litter that will be dropped down into the borehole.
Image copyright WA Museum 

This technique is used to sample troglofauna, breathing animals living underground such as woodlice, insects, spiders, scorpions and their relatives, which can only survive in subterranean habitats and are typically pale in colour and eyeless.

Digging, netting, sampling

Diving beetles called stygofauna, also live in underground aquatic environments. The method employed to sample these organisms in very small habitats is quite the same as the previous method. The scientists need to find and get access to a borehole once again. However, they don’t use leaf litter, but a cone shaped sampling net made of fine mesh and with a collecting tube at the bottom. Using a piece of fishing line, researchers drop the weighted nets down the holes and pull it back up through the water column, catching organisms living in the groundwater. The tubes are put into a collecting preservative and bought back to the Museum for further study.

Image of a net used for collecting

Example of a sampling net used to collect aquatic subterranean fauna.
Image copyright WA Museum 

Image of a collecting tube containing diving beetles

In this photo we can see many little diving beetles swimming around in the collecting tube.
Image copyright WA Museum 

Piping, pumping, picking

Each habitat requires a different technique. To sample inhabitants of the hyporheic zones, found in gravels below and next to rivers and stream beds, scientists drive a pipe down into the gravel and the rocky substrate of a dry gravel stream until the groundwater is reached. The distance between the surface and the water table is sometimes measured in tens of centimetres, sometimes in metres. Then, the research team attach a hand pump to the pipe and pump the water out into a bucket and a sieve. If there is a fauna to study, organisms pumped will be trapped in the sieve. In these small habitats, called “interstitial spaces” underneath and next to the riverbank, lies a very specified fauna including in particular water mites, ostracods and copepods modified to live in these environments. 

Man kneeling beside a river

Sampling in the hyporheic zone.
Image copyright WA Museum 

Further Information

To learn more about subterranean biology see this talk given by Dr Bill Humphreys about life underground, or a talk Presented by Dr Mark Harvey about the methods employed by scientists to study the subterranean fauna.