- Southern dusky salamanders used to be abundant in Georgia, Florida and parts of Alabama. But that all changed in the 1970s when researchers started noticing sudden declines throughout their distribution.
- Today, southern duskies are found in less than 1 percent of their former range.
- Researchers are conducting the first range-wide study of the species to try to figure out why exactly so many have vanished and what their disappearance has meant to the surrounding environment.
- The researchers say they hope their results can be used to prevent the southern dusky from becoming extinct, as well as help save other declining salamander species.
TALLAHASSEE, Florida — Biologists Chace Holzheuser and Bruce Means are on their hands and knees in a Florida swamp, pawing through dark water, leaves and muck as cicadas hum unceasingly in the treetops far above them. Suddenly, Means lurches forward.
“Got one!” he yells. He turns around and carefully opens his hands to reveal a tiny dark salamander. It’s smaller than a baby carrot and has a long tail and short legs that belie its agility as it attempts a surprisingly effective leap to freedom. But Holzheuser is ready and catches it mid-air. He puts it in a clear plastic sandwich bag so we can get a better look.
What at first seemed like a nondescript, uniformly mud-colored creature turns out to have striking reddish spots along its sides, each with an even smaller light spot inside them. They lead up to large orange patches behind the salamander’s cheeks that are reminiscent of ears – which, it turns out, is how it got its Latin name: Desmognathus auriculatus.
This is the southern dusky salamander, a species that once occurred from Georgia, through much of Florida and into southern Alabama. In the 1940s and 1950s, it was easy to find southern duskies. So much so, in fact, that scientists regarded the species as the most abundant salamander in its habitat.
But that’s no longer the case. In the mid-1970s, scientists started noticing that many populations had suddenly vanished. Today, the southern dusky salamander is gone from almost all of its historic range.
And nobody knows why.
But Holzheuser is trying to solve this mystery. He’s embarked on a multi-year study to figure out what happened to them in the hopes of that it will help pull them back from the edge of extinction.
He’s hoping his study’s results will not only help save southern duskies, but other salamander species as well.
Unlikely inhabitants
Southern dusky salamanders are members of the dusky salamander genus Desmognathus, which comprises some two-dozen species found in the U.S. east of the Mississippi River. All Desmognathus species have a unique adaption – they open their mouths upside down. Most jawed animals open their mouths by swinging their lower jaws down. But not dusky salamanders. For them, the lower jaw remains stationary while the upper jaw and the cranium swing upward, making them look a bit like enthusiastic headbangers when they’re eating.
Desmognathus is nested in Plethodontidae, a huge family of salamanders native to North America. Plethodontid salamanders are distinctive in that they lack something that most other terrestrial vertebrates have: lungs. Instead of lungs, these salamanders breathe through their skin and by gulping air into their mouths, which are lined with tissue filled with oxygen-absorbing blood vessels.
Because they don’t have lungs and rely on their skin to absorb oxygen, plethodontids tend to be quite small – the size of your pinkie finger or smaller – and can live only in wet, cool areas where their skin can remain moist.
Most dusky salamander species live in cool stream habitats in the Appalachian Mountains. But a few, including the southern dusky, are also found in an area of southeastern North America called the Coastal Plain. Stretching more than 3,000 miles from Massachusetts to Texas and down the Atlantic coast of Mexico, the Coastal Plain is a seaward-sloping skirt of land full of swamps and streams that boasts dramatic biodiversity.
The Coastal Plain is home to more than a thousand plant species found nowhere else in the world. It’s also a paradise for amphibians with more frog species living here than anywhere else in the U.S. and Canada. And it boasts six of the planet’s nine families of salamanders.
Several dusky salamander species are native to areas of the Coastal Plain in Georgia and Florida. But this shouldn’t be the case, given how hot and sometimes dry the region is. So how are amphibians whose ancestors evolved in cool, moist Appalachian ecosystems able to live down here?
Herpetologists think it has something to do with a geological oddity called a “steephead.” Found most commonly in Florida, steepheads are spring-fed ravines that form backwards as soil erodes towards the spring. At the bottom of each ravine runs a cold, clear stream. As time advances, the steam gets longer and the ravine gets steeper and deeper. Some steepheads can be more than 80 feet deep, cutting dramatic, branching canyons in Florida’s otherwise pancake landscape.
Steephead ravines are microhabitat refuges for animals and plants that wouldn’t normally be able to persist in the southern U.S. The cold springs that form them flow year-round, keeping the bottoms perpetually wet and significantly cooler than the land above – the perfect oasis for an amphibian whose ancestors evolved in northern mountain streams.
Researchers believe these steepheads allowed dusky salamanders to colonize the Coastal Plain of the southern U.S. And once they got there, they diversified into several species – among them the southern dusky.
A “shocking” disappearance
Southern dusky salamanders were once thought to range all the way from Virginia to Texas. However, recent studies indicate that the western and northern populations belong to different species and that true southern dusky range is limited to Florida, parts of Georgia, and just over the border in Alabama.
Surveys of southern dusky populations in the 1940s to 1960s found lots of them in these areas. So many, that it was considered the most abundant salamander species where it was found.
But all this changed sometime around 1970 when, seemingly simultaneously, almost all of the hundreds of known populations crashed.
“We’ve identified the period of decline starting in at least the late 1960s and going until 1977,” Holzheuser said. “From 1977 to now, we have not seen any sort of rebound in those populations where they’ve disappeared. We’ve gone back to pretty much all of the original populations, we’ve identified 300 sites throughout Florida where they used to occur, where they were verified and documented before the 1980s, and we’re only finding them in a handful of river systems.”
Overall, Holzheuser and his colleagues have found that the range of southern dusky salamanders has shrunk by more than 99 percent. They’re now completely gone from Alabama and are found only at a handful of sites in Georgia and the Florida panhandle.
“I find it quite shocking that such a large disappearance could’ve occurred in such a short amount of time across a large geographic area,” Holzheuser said.
Holzheuser isn’t the only researcher perplexed by the sudden decline of southern dusky salamanders.
“I spent a whole year on my hands and knees crawling around in several hundred ravines and found zero– absolutely none,” said Bruce Means, a research ecologist and professor at Florida State University in Tallahassee. Means also runs the Coastal Plains Institute, a nonprofit organization that aims to help preserve the biodiversity of the southeastern U.S.
Means has been studying dusky salamanders for decades, and was part of the research team that discovered northern and western populations of southern duskies were actually different species. His work placed him front and center when southern duskies started vanishing and he has coauthored several papers on their decline.
But so far, researchers like Means haven’t been able to find a smoking gun that explains how so many salamanders in so many places vanished so quickly. They do, however, have a few ideas, which is where Holzheuser comes in. He’s embarking on the first range-wide study of the southern dusky salamander as part of his PhD work at Florida State University, during which he’ll be documenting how many are left, where they are and what they eat, and trying to figure out why exactly so many have vanished.
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Pollution, pigs and pathogens
The Florida panhandle looks pretty different today than it did in the 1950s. A drive outside Tallahassee reveals miles and miles of suburban sprawl and cleared land, with new and widened roads to connect the sprawl.
“It’s all over,” Means says with a dry chuckle.
Underlying this new development is honeycombed, porous limestone that feeds water coming from above to the aquifer below.
“Our great water supply in Florida comes from that limestone,” Means says. “Everything we do on the surface works its way down into the limestone and comes out in our tap water.”
And not just tap water. Pollution is also affecting the region’s wetlands. Holzheuser brings up Wakulla Springs, a freshwater spring and cave system 14 miles south of Tallahassee.
“Wakulla Springs used to be crystal clear – I mean it used to be clear enough that they would film underwater movies at this place,” he says. “But because of Tallahassee’s urban growth, the drainage has leached into the aquifer system. And now the water coming up is brown. They don’t even run glass-bottom boats anymore because you can’t see the bottom.”
Because of their thin, porous skin, salamanders and other amphibians are particularly sensitive to water pollution. For instance, research has linked the emergence of hermaphroditic frogs in suburban Connecticut ponds to runoff of the herbicide Atrazine from nearby farm fields. Pollution can also indirectly harm amphibians; studies have implicated parasitic flatworms as a cause of grotesque frog malformations, parasites spread by snails that had proliferated due to fertilizer runoff.
So could increased levels of water pollution have killed off southern dusky salamanders? Maybe, say Means and Holzheuser. But one confounding factor to this hypothesis is that many areas from which the southern dusky disappeared are still home to other salamanders species, even other kinds of duskies. If pollution levels were high enough to kill off one kind of salamander, why weren’t others as affected?
Feral hogs are also a big problem in Florida, as they are in pretty much all the other places they’ve been introduced. The U.S. Department of Agriculture estimates they cost the country around $1.5 billion every year for crop damage and control measures. And a study published in Nature’s Scientific Reports earlier this year singles out pigs as one of the most harmful invasive species in the world when it comes to conservation, one that poses a threat to more than 87 percent of imperiled species in the contiguous U.S.
For salamanders, hogs pose a double threat.
“One is that they root up the environment and they eat salamanders directly and/or they destroy the breeding habitat of the salamander,” Means said. Though he added that he doesn’t think pigs could completely wipe out an entire population.
“The other is that they can be carriers of pathogens.”
One of these pathogens is the amphibian chytrid fungus Batrachochytrium dendrobatidis (Bd). First detected by scientists in the 1970s, Bd spread quickly around the world and has been implicated in the declines or extinctions of around 200 amphibian species. While Bd seems to have a preference for frogs, salamanders can also be infected.
So far, Holzheuser says he and his colleagues “haven’t found a whole lot of evidence to suggest that Bd was the cause.” But since you can only test for one kind of chytrid fungus at a time (and there are a lot of different kinds of chytrid out there) he says that it’s possible they haven’t looked for the right one yet.
But there’s a wrench in this hypothesis, too: in the few places where southern dusky salamanders still live, they seem to be doing pretty well. One of these is along the Sopchoppy River in Apalachicola National Forest.
“Whatever affected the rest of the population for some reason skipped over this entire area,” Holzheuser said. “And given that there’s so much flow of invasive species and human traffic through here, you would think that if it was a pathogen of some sort then it would’ve been introduced by one of these many carriers that come in and out of the area, especially because they’ve disappeared from river systems so close to this one.
“So if it is a pathogen, we have to come up with an explanation as to why it did not invade this specific region.”
Critical habitat
Encompassing more than 600,000 acres, Apalachicola National Forest is Florida’s biggest such forest. It’s situated about 50 miles from Tallahassee and comprised of dense forest, winding rivers, and swamps the color of over-steeped tea. It’s also home to the largest known population of southern dusky salamanders left in the world.
Driving down the road to Holzheuser’s Apalachicola study site is like going back through time. Rural development and open land give way to tracts of longleaf pine (Pinus palustris) that get thicker and taller and older the deeper we go into the national forest. While none of this is intact forest – nearly all forests in the southeastern U.S. have been logged over the last few centuries – its status as a protected area means it’s been given a chance to grow back and provide important habitat for plants and animals that have few other options.
“An awful lot of [terrestrial] animals in the southeastern United States that are considered endangered or threatened lived in this kind of environment,” Means says. “And there’s less than 2 percent of it left now from Virginia to East Texas.”
Southern dusky salamanders aren’t the only rare animals found in Apalachicola National Forest; Holzheuser points to some pines marked with white paint, which he says indicates they’re used as nesting trees by endangered red cockaded woodpeckers. The only bird known to excavate holes in living trees (apparently by infecting them with a wood-decaying fungus), these woodpeckers make certain holes in which to roost and other ones in which to nest. There’s an easy way to distinguish which are nesting holes, even from the ground: the nest holes are framed by moats of sap.
“They’ll scrape around the edge of the hole to make the sap drain like that to protect the hole from predators like snakes,” Holzheuser says.
At the study site, Holzheuser and Means have no trouble finding southern dusky salamanders, catching one before barely getting their boots wet. As they venture further into the blackwater swamp, they catch another and then another as huge spiders watch warily from the trunks of black tupelo and cypress trees growing right up out of the water.
“Unfortunately, what you see here gives you a jaded view because everywhere else in Florida they used to be this abundant,” Holzheuser says. “However, they’re not anymore. If we go to a river system that’s immediately adjacent to this one, we won’t find anything at all.”
According to Holzheuser, all known remaining southern dusky salamanders are found only in protected areas – places like national and state forests and wildlife refuges – that have been spared the levels of development experienced by much of the rest of the region.
Holzheuser and Means think another clue to the salamanders’ success here might be the extreme acidity of the water. Most natural water bodies in the U.S. have pH values between 6.5 and 8.5. Acid rain has a pH of around 4.3 and many, if not most, aquatic and semi-aquatic animals can’t live in water with a pH value below 5.
But at Holzheuser’s study site, one of the last strongholds of the southern dusky salamander? The pH here can be as low as 3.2.
“The acidity comes from the decomposition of all this organic matter, and that’s what turns the water black as well,” Holzheuser says. “So [southern dusky salamanders] are highly adapted to acidic environments. But we did find them in spring-type habitats as well like the steephead springs, which are more basic. So they can obviously tolerate a range of acidities in their habitat.”
Could this acidity be keeping something, a pathogen perhaps, out of the water at this study site? Holzheuser hopes his study will provide the answer.
He’s also examining the stomach contents of southern duskies to figure out what they eat and how their disappearance has affected the surrounding environment. He does this by giving salamanders “gastric lavages” – a pretty word for a stomach pump – that induce vomiting while not harming the animals.
“Given their abundance, southern dusky salamanders were probably pretty impactful on the carbon cycles of these steams because they consume a lot of the arthropods and other creepy-crawlies that are in the streams,” he said. “And with them being gone, a lot of those insects are left to reproduce in high abundance. So the stream’s actually lost an important predator with their disappearance.”
Preparing for disaster
Once he finishes up his study next summer, Holzheuser’s planning on using it to try and convince the federal government to list the southern dusky salamander as endangered. This would open up more avenues and funding sources for its conservation, which both Holzheuser and Means say are sorely needed if the southern dusky is to be saved.
“And if we are able to find that cause, then that’s the first step in fixing it,” Holzheuser said. “If we can fix the problem and prevent the species from going extinct and help them spread back to their original habitat, I think that as a biologist and a conservationist, that’s the number one goal for me – that’s the gold medal.”
While Holzheuser’s main goal is to shed light on the plight of the southern dusky, he says the results of his research could also be used to help other salamander species in the U.S. Specifically, his findings could provide information about what happens in the event of cataclysmic salamander die-offs due to, say, a fast-spreading disease.
Such a situation may not be that far-fetched – and it may not be that far off. In 2008, a mysterious disease started killing fire salamanders in the Netherlands; since then, it has wiped out more than 99 percent of fire salamanders in affected areas in the Netherlands, Germany and Belgium. In 2013 scientists identified the culprit: Batrachochytrium salamandrivorans, or Bsal, a chytrid fungus related to Bd. But unlike Bd, Bsal targets salamanders.
While Bsal hasn’t yet been detected in the U.S., researchers believe it’s just a matter of time until it gets here. And they say that when it does, it could be devastating. North America is the world’s hotspot of salamander species richness, and the U.S. has more salamander species than any other single country. Preliminary research suggests half of all U.S. species could be susceptible to Bsal. Plethodontid salamanders like the southern dusky seem to be particularly affected.
Holzheuser says the southern dusky probably isn’t as at-risk as many other salamanders given that Bsal prefers places cooler than Florida, but the prospect of a U.S. Bsal invasion still scares him. And his tests do indicate that southern duskies are susceptible to Bsal infection.
“The fact this species is in such a precarious position is really kind of frightening to me,” Holzheuser said. “And what I really want to emphasize is the disappearance of this species and our investigation of that disappearance is not just for this one species – it’s for all salamanders in the U.S.
“This can be a case study to show what happens to a species if it goes extinct, how it can go extinct, and what happens [ecologically] as a result of that.”
Banner image: A southern dusky salamander, courtesy of Chace Holzheuser.
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