🔗 Share this article Galápagos Had No Indigenous Amphibians. Until Hundreds of Thousands of Frogs Arrived On her daily walk to the scientific station, biologist Miriam San José crouches near a shallow pond covered by dense vegetation and collects a small plastic sound recorder. The device was left there overnight to capture the characteristic croaks of the Fowler's snouted treefrog, recognized by local scientists as an invasive species with consequences that experts are starting to comprehend. Despite teeming with remarkable wildlife – such as ancient giant tortoises, swimming iguanas, and the famous finches that sparked Charles Darwin's theory of evolution – the Galápagos archipelago off the shoreline of South America had historically been devoid of frogs and toads. During the 1990s, this shifted. Several tiny amphibians made their way from continental Ecuador to the islands, probably as stowaways on transport vessels. Fowler’s snouted tree frogs came in the 1990s and have taken hold on multiple Galápagos islands. DNA studies suggest that, through time, there have been repeated unintentional arrivals to the archipelago, and the frogs now have a strong presence on several islands: Isabela and Santa Cruz. The numbers is expanding so quickly that researchers have been struggling to keep track, calculating numbers in the millions on each island, across developed and agricultural areas, but also in the conservation Galápagos national park. When San José marked amphibians and attempted to find them in the following week and a half, she could find only a single tagged frog from time to time, indicating their numbers were enormous. They estimated 6,000 frogs in a single pond. "Our estimates are still very conservative," states the researcher. "I'm quite certain there are even more." Acoustic Chaos and Growing Concerns The amphibians' proliferation is clear from the acoustic chaos they cause. "The number of frogs and the noise – it's really incredible," comments the scientist. For the researchers, their nightly mating calls are useful in estimating their presence in remote areas, using recorders like the one near the office. But local farmers say the calls are so raucous they keep them up at night. "During the wet season, I constantly hear their croaks and they're extremely loud," says a local coffee farmer from the island. "At first it was a shock, observing the initial frogs in the area," says Larrea Saltos, who started noticing their large numbers about several years ago when one jumped on her hand as she was stepping out of her front door. Ecological Impact Remains Unclear The sound isn't the primary problem, though. While the species has been in the Galápagos for almost three decades, scientists still know very little about its impact on the islands' delicately balanced land and water ecosystems. Scientists are discovering more about the frogs, including that they can remain as larvae for as long as six months. On archipelagos, it is very typical for non-native species to prosper, as they have none of their enemies. The Galápagos counts 1,645 invasive species, many of which are seriously disrupting the survival of its endemic ones. A 2020 research indicates the non-native amphibians are hungry bug consumers, and might be disproportionately consuming rare bugs found only on the islands, or depleting the food sources of the islands' rare avian species, disrupting the food chain. Unique Characteristics and Control Challenges The Galápagos amphibians have shown some atypical traits, including surviving in slightly salty water, which is rare for amphibians. Their metamorphosis process is also extremely inconsistent, with some larvae becoming frogs very quickly and others taking a extended period: the researcher witnessed one which remained as a larva in her lab for half a year. "We really don't know this part," she says, concerned the larvae could be impacting the region's freshwater, a very scarce resource in the islands. More research is required to establish the best way to control the amphibians without affecting other organisms. Techniques to curb the frogs in the beginning of the century were mostly unsuccessful. Park rangers tried capturing significant quantities by manual methods and gradually increasing the salt content of lagoons in vain. Studies indicates spraying caffeine – which is extremely poisonous to frogs – or using electrocution could assist, but these approaches aren't always safe for other rare Galápagos species. Without answers to more of the basic issues about their lifestyle and impact, culling the amphibians might not even be the right way to proceed, says the biologist. Funding Challenges for Study While she expects the growing use of environmental DNA techniques and DNA examination will help her group make sense of the invader, financial support for the research has been difficult to come by. "Everyone wants to give funding for preserving frogs," says the researcher. "But it's more difficult to find funding for an invasive frog that you might want to control."