When Batrachochytrium dendrobatidis, or Bd, emerged in the mid-twentieth century, scientists and conservationists watched helplessly as the fungus swept like a biblical flood through amphibian populations across the planet. Commonly known as chytrid, the disease spread rapidly and crippled nearly every new amphibian species it encountered, exhibiting a particular violence towards frogs and toads. It soon claimed 90 species and affected nearly 500 others.
Chytrid hit so hard and spread so quickly that by the time the public knew what it was around the late 1980s, there was little chance to save many of these affected species. For that reason, some have called Bd an ecological supervillain. Others refer to it as the doomsday fungus. Both monikers, regrettably, tend more toward fact than hyperbole.
Today, we’re on the brink of another outbreak.
As Bd continues its rampage among toads and frogs, a new insidious threat has begun to emerge, this time targeting a different class of amphibians: salamanders. In 2013, scientists described a second species of chytrid fungus, Batrachochytrium salamandrivorans, or Bsal, when it arrived in Europe from Southeast Asia and spread to the vulnerable fire salamanders of the Netherlands. Living at the edge of its geographic range and confined to small populations with low genetic diversity, this species stood as a perfect target for the fungus. In three years, fire salamander numbers declined by 96 percent. The scientific name of the fungus, which means “salamander devourer” in Latin, rang true: It was indeed the devourer of salamanders.
In the southeastern United States, a hotspot of salamander biodiversity, the amphibians are safe from this new chytrid fungus, for now. But as scientists watch the demise of the fire salamanders from across the sea, many of them agree: Bsal is on its way.
“We have to think of it as more of a matter of when it gets here than if,” says Debra Miller, a professor at the University of Tennessee and a co-leader of the disease task team with Southeast Partners in Amphibian and Reptile Conservation. “With all the salamander species we have throughout Appalachia, we could lose a huge portion of them.”
Roughly 20 percent of the world’s salamander species live in the American Southeast. Many of them make their home nowhere else on the planet. The region contains numerous examples of isolated species living in small populations, vulnerable to a quick extinction with any sort of disruption to their health or environment much like the fire salamander. There’s the Pigeon Mountain salamander, for example, endemic to a single mountaintop in the state of Georgia, and the Black Warrior waterdog, found only within the Black Warrior River Basin in Alabama. There’s also the South Mountain gray-cheeked salamander, the Peaks of Otter salamander, the Caddo Mountain salamander — and the list goes on.
It’s the same environmental anomalies that make the Appalachian region such a perfect home for salamander biodiversity that have also led to this sort of speciation and separation. Over the millions of years salamanders have evolved in the Southeast, the various mountain ranges and elevation gradients have acted as natural barriers to connectivity. Certain species prefer lower elevations while others prefer higher, and this separation has led to the emergence of unique populations in isolated regions.
But that speciation makes some of these species particularly vulnerable. Any small disturbance here — habitat destruction, climate change, or, perhaps most menacingly, an invasive fungal infection like Bsal — could spell immediate doom.
As the advent of Bsal approaches, many scientists are preparing for its onslaught. Having learned harsh lessons from Bd, they carry a haunting sense of déjà vu. But they also see this next wave of chytrid as a second chance at saving amphibians and preempting another extinction crisis. “When Bd first hit, we didn’t know anything,” Miller says. “We’re still learning, and now investigating Bsal as well.”
Mystery still shrouds much of the biology and virulence of these diseases, and therefore inhibits attempts to create effective treatment protocols. This lack of understanding is one of the primary reasons that Bd has been so destructive to amphibians, and why Bsal would be too.
Ordinarily, the response to this sort of marauding infection would be to secure a captive population of the imperiled species in order to shield at least some portion from the disease, and to enable the possibility of reintroduction once the environment can again support them. But Miller is quick to point out that captive propagation programs — often referred to as ex situ conservation — are notoriously difficult to carry out for even a single species, not to mention the dozens that would be impacted simultaneously if Bsal were to reach the Southeast.
They have certainty proved challenging in the case of toads and frogs at risk from Bd. “We lost a lot of species because we didn’t know how to successfully care for and breed these animals in captivity,” Miller says. In the case of vulnerable salamanders, she suggests that we learn from the past and use the time we have to prepare ahead of Bsal’s arrival.
“I don’t think it would be a far-fetched idea at all to have something in place to do [ex situ],” says Miller. “And we don’t need to wait until it gets so close that it’s a last resort.”
There exists a tendency in conservation to rarely initiate ex situ programs until the threat has already begun taking its toll. For a menace like Bsal — one that we know is coming — a last resort measure could perhaps be better seen as a preemptive defense against an imminent onslaught.
“When we think of conservation, we think of intact systems and wild animals in those systems thriving,” says Kat Diersen, Southeast representative for Defenders of Wildlife. “Ex situ conservation is not that. Ex situ is Noah’s Ark.”
Diersen acknowledges the difficulty in breaking from these traditional views, but also recognizes the unique danger Bsal poses to the vulnerable biodiversity of southeastern salamanders. “These are animals that are challenged on multiple fronts,” she says. “Their adaptive capacity, their representation, their redundancy and their resiliency are all hugely negatively impacted. For those species, the introduction of a disease? It could be an overnight wipe-out,” she adds, snapping her fingers, her eyes cold, her face set grimly. “For most species, ex situ conservation would normally be considered extreme measures, but for southeastern salamanders it’s going to need to be a foundational element of our strategy for saving them.”
Ex situ conservation requires huge amounts of money, capacity, collaboration and commitment — and belief, at the end of the day, that these expenditures are worthwhile and that the salamanders of the Southeast are worth investing in. This shift toward preemptive conservation requires a fundamental change in practices, fueled by an influx of public support.
Even if this support materializes, realistically, these efforts will be confined to the most vulnerable species. And while screening efforts are in place to prevent Bsal’s arrival through the pet trade, they are admittedly inadequate to reliably stop the pathogen in its tracks.
That’s why other conservation avenues must also be pursued if we are to become truly ready for Bsal’s eventual landfall. It is this understanding that drives the work of Diersen and her partners.
“These diseases are going to come,” says Diersen. “The best thing we can do for species in the wild that are facing these threats from all directions is to give them the resiliency they need to bounce back from a systemic event like the introduction of disease. If we can connect, protect and restore their habitat, their overall adaptive capacity will be greater. We know what these creatures need: protection, restoration, connectivity. Those are the key.”