During the first World Congress of Herpetology in 1989, several amphibian biologists were sharing their studies when they realized all of the findings were strikingly similar: amphibians were dying off at an abnormally fast rate in the 1980s. Joseph Mendelson, the director of research at Zoo Atlanta, recalled that the scientists were having trouble locating known populations of frogs in several countries such as Costa Rica, the US, and Australia.
The findings culminated a worldwide comprehensive survey of 5,000-plus species of amphibians conducted by these scientists. The 2014 study published in Science demonstrated that amphibians are far more threatened than either birds or mammals. The researchers found that 30% of amphibian species were at risk of extinction. Since then, more surveys and studies about amphibian extinctions have followed. A 2013 national survey, for instance, revealed that amphibian populations in the US declined at a rate of 3.7% a year from 2002 to 2011.
According to Vox, a liberal-leaning American news and opinion website owned by Vox Media, a 2010 survey of 25,780 species of vertebrates found that 41% of the amphibians were threatened with extinction. “On a per-species basis, amphibians are in an especially dire situation, suffering the double jeopardy of exceptionally high levels of threat coupled with low levels of conservation effort,” the study noted.
Why Amphibians Are Dying Off at an Abnormal Rate
Amphibians, a unique group of vertebrates containing over 7,000 known species, are threatened worldwide. These animals have existed on our planet for over 300 million years. However, they have been facing an alarming number of extinctions in the past few decades. Nearly 168 species are believed to have gone extinct and at least 2,469 (43%) more have populations that are declining. These findings indicate that the number of extinct and threatened species will probably continue to rise.
While the major factor why amphibian populations continue to decline is habitat destruction, the recent cause of the amphibian collapse is an emerging disease called chytridiomycosis, a disease caused by the fungal chytrid pathogen Batrachochytrium dendrobatidis. Previous studies associated this pathogen with the global loss of hundreds of species of amphibians and represents a spectacular loss of biodiversity. The disease, which is also called BD, is thought to be the main culprit behind the 200 frog species extinctions seen in the past several decades.
Reid Harris, a biologist and director of international disease mitigation at the Amphibian Survival Alliance, said that BD is known to infect pretty much every species of amphibian. The journal Nature reported in 2012 said that this makes "the greatest disease-driven loss of biodiversity ever documented.” A 2019 study found out that the deadly disease has the worst impacts on Australia, Central America, and South America.
"The disease is caused by the chytrid fungus, which likely originated in Asia where local amphibians appear to have resistance to the disease," lead researcher Dr. Ben Scheele from the Fenner School of Environment and Society of the Australian National University (ANU) said.
According to Science Daily, an American website that aggregates press releases and publishes lightly edited press releases about science, the findings revealed that the disease has caused dramatic population declines in more than 500 amphibian species, including 90 extinctions, over the past 50 years. However, this will not end here. Over the next 10 to 20 years, many amphibian species will still be at high risk of extinction due to chytridiomycosis. "Knowing what species are at risk can help target future research to develop conservation actions to prevent extinctions,” Scheele said.
The disease was mainly driven by globalization and wildlife trade, enabling to spread more in animals. A groundbreaking study published in 2018 revealed that the fungus most likely emerged in the Korean peninsula, sometime during the 1950s. The scientists theorized that human activities inadvertently spread it far and wide, which led to amphibian die-offs across the Americas, Africa, Europe, and Australia.
“[The pathogen's spread] could have happened from any one event, from the cumulative number of events, or maybe some big anthropogenic events like the Korean War,” lead author Simon O’Hanlon from the Imperial College London said.
Long Lost Toad Species Back From Extinction
The deadly disease has heavily infected frogs, leading to the extinction of some species. One of these frog species is the Atelopus mindoensis, commonly known as the Mindo harlequin toad. The toad hadn’t been seen alive in 30 years. The chytrid, which can disrupt the animals’ ability to absorb oxygen and water through their skin, has hit species within the Atelopus genus harder than most. The rediscovery of the harlequin toad gives hope to scientists that many amphibian species can come back from extinction.
Since the 1980s, more than half of the harlequin toad species haven’t been seen. Several species of Atelopus are currently classified as either threatened, critically endangered or presumed extinct. According to National Geographic, an American pay television network and flagship channel that is owned by National Geographic Partners, the reappearance of the toad makes it the ninth species in the Atelopus genus to come back from the dead since 2003.
“Every Atelopus species that is 'rediscovered' highlights the importance of continued surveillance, and the opportunity we have to learn from these resilient creatures about the mechanisms of recovery after epidemics," Cori Richards-Zawacki, a herpetologist at the University of Pittsburgh, said.
The toad was discovered by University of New Brunswick scientists last August 2019. Since then, they have seen toads five more times when they returned to the same reserve. They found out that several amphibians have developed a resistance to chytrid. Among them: Sierra Nevada yellow-legged frogs, variable harlequin frogs, and common rocket frogs. However, Jamie Voyles, a disease ecologist at the University of Nevada in Reno, said that there hasn’t been enough testing to know the true scope of the recovery.
“We know from lots of diseases, including the current pandemic, that infectious diseases and outbreaks tend to subside. There’s an outbreak stage, but then frequently, there's a drop-off in terms of the severity of disease within a population. And so we have experienced a similar thing with amphibians,” Voyles said.