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Tiny subterranean Texas salamanders could be extinct in 100 years

  • A recent study has revealed the existence of three previously undescribed species living underground within an aquifer system in Central Texas.
  • The authors say one of these species is critically endangered due to human over-use of the aquifer. In all, they say that this unsustainable use could mean the extinction of all aquifer salamanders in the next century.
  • The researchers urge the creation of policies that would regulate groundwater usage, as well as greater protection of particularly at-risk species through the U.S. Endangered Species Act.

There’s another world beneath the soil of Central Texas, one that is dark, wet, and mysterious. It’s an isolated kingdom ruled by a unique group of underground salamanders. Now, new research has officially added three new species to its roster.

But this world is not safe from aboveground pressures, and the researchers who discovered these new species say one is already critically endangered. Their study, published in Proceedings of the National Academy of Sciences, also indicates another previously described species is much more imperiled than they thought.

The researchers write that, ultimately, all of the underground salamanders living in this particular aquifer system could disappear in the next century.

An ongoing mystery

Central Texas is underlain by limestone, which over millennia has been eroded by water to form aquifers comprised of vast mazes of caves and channels. The top predators in here are small, pale aquatic salamanders of the Eurycea genus that have evolved to live their lives entirely underground. Many are blind or nearly so, having no need to see when their world is pitch black.

Researchers still know relatively little about them, including how many there are or even what they eat.

“We don’t know that all that much about their diet, but generally any aquatic invertebrate they can fit in their mouth, and perhaps the occasional other salamander (if it’s small enough),” said study coauthor Tom Devitt, who was a post-doctoral researcher at UT Austin when he conducted the study and is currently an environmental scientist with the City of Austin’s Watershed Protection Department.

Austin blind salamander (Eurycea waterlooensis), one of the species that lives in the aquifer below Central Texas. Photo by David Hillis.

The way water flows in this underground ecosystem has isolated some salamander populations from others, which has given rise to multiple species in a single aquifer. But because the caves can be so small and extend so far underground, researchers still don’t know exactly how many species there are. And even salamanders that have already been collected haven’t been genetically analyzed to see how related they are to others.

To help address this issue, Devitt and his colleagues at the University of Texas at Austin sequenced the DNA from more than 300 salamanders collected throughout the Edwards-Trinity aquifer system, which extends some 200 miles (around 300 kilometers) from Austin down to San Antonia and over to the border with the Mexican state of Coahuila. Their results reveal several more species live there than previously thought. The three new species have yet to be named and occupy very different parts of the aquifer system.

Researchers think there may still be much to learn about the amphibian inhabitants of the Edwards-Trinity aquifer system. But access to them can be difficult, if not impossible.

“There have been salamanders observed several hundred feet down in the aquifer, but we really don’t yet know how deep they can live,” said study coauthor David Hillis, a professor of integrative biology at UT Austin.

Compounding the problem of depth is that many of the channels and caves inhabited by salamanders are way too small for humans to squeeze through. Hillis said they’ve gotten around this in the past by sticking cameras into some of these more restricted portions.

Study coauthor David Hillis explores a rare human-size area of the aquifer. Photo courtesy of David Hillis.

“We are developing methods to amplify environmental DNA from wells, so that we can ‘see’ what is down there without trapping or finding salamanders on underwater video cameras,” Hillis told Mongabay.

Environmental DNA, or eDNA, is genetic material from skin, scales, hair, or waste products collected from where an organism lives rather than from the organism itself. Using eDNA can be very useful for researchers studying animals that are hard to find – or hard to reach.

An uncertain future

Salamanders aren’t the only ones that rely on the Edwards-Trinity aquifer system. It also provides water for millions of people who live in the region, as well as for industry and agriculture. This, say the researchers, is putting a lot of pressure on the aquifer system – and the animals that live in it.

“Significant water table drawdown has already occurred over large portions of the study area, especially in the northern segment of the Edwards Aquifer,” they write. “Intensive pumping in the Trinity over the last several decades has resulted in water table declines, decreased well yields, and diminished baseflow to springs and streams.”

David Hillis climbs down a well to check on the aquifer. Under Texas state law, there is no limit on the volume of groundwater a landowner is allowed to pump from a well like this. Photo courtesy of David Hillis.

The researchers write that because of human water use, all salamander species in the Edwards-Trinity aquifer system are highly vulnerable to extinction in the next century. Of particular concern is one of the newly discovered species, a tiny golden creature that is only found in a restricted area west of Austin, which the researchers say qualifies as critically endangered. Their study also indicates that the Georgetown salamander (Eurycea naufragia), already considered threatened, has a far smaller distribution than previously thought and is likely more endangered.

A big problem, write Devitt and his colleagues, is that Texas considers its groundwater to be private property governed under rule-of-capture law. This basically means it’s used as a first-come, first-serve resource with no enforceable regulations aimed at maintaining aquifer levels.

“The rule-of-capture law for groundwater was adopted from British common law when Texas became a republic in 1836,” Devitt said, calling the law “very outdated” and adding that it “predates our knowledge of the hydrologic cycle and our understanding of aquifers.”

The researchers recommend the creation of policies that would regulate groundwater usage, as well as greater protection of particularly at-risk species through the U.S. Endangered Species Act.

“I think the U.S. Fish and Wildlife Service should review the status of all these salamanders in light of the new evidence,” Hillis said. “They are part of the rich biological heritage of Texas, and losing these groundwater salamanders would be a huge loss for our state’s biodiversity.

“Importantly, protecting these salamanders also means protecting the quality and quantity of fresh water that Texans rely upon.”

 

 

Banner image: One of the three newly identified species of salamander in the Edwards-Trinity aquifer system. This one, which lives only in one small area west of Austin, is considered critically endangered. Photo by Tom Devitt.

Citation: Devitt, T. J., Wright, A. M., Cannatella, D. C., & Hillis, D. M. (2019). Species delimitation in endangered groundwater salamanders: Implications for aquifer management and biodiversity conservation. Proceedings of the National Academy of Sciences, 201815014.

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