🔗 Share this article Galápagos Lacked Any Indigenous Amphibians. Then Hundreds of Thousands of Amphibians Made Their Home During her daily walk to the scientific station, scientist the researcher crouches near a small water body covered by dense plants and collects a small green audio recorder. The device was left there overnight to capture the characteristic croaks of the Scinax quinquefasciatus, recognized by local scientists as an invasive threat with consequences that experts are starting to understand. Although teeming with unique animals – such as ancient giant tortoises, swimming lizards, and the well-known birds that inspired Charles Darwin's theory of evolution – the Galápagos archipelago near the coast of South America had long remained devoid of frogs and toads. In the late 1990s, this changed. Several tiny amphibians made their way from continental Ecuador to the archipelago, probably as hitchhikers on transport vessels. The invasive species arrived in the 90s and have taken hold on multiple Galápagos islands. Genetic studies indicate that, through time, there have been multiple unintentional arrivals to the archipelago, and the amphibians now have a firm foothold on two locations: Isabela and Santa Cruz. The numbers is growing so quickly that scientists have been struggling to keep track, calculating numbers in the millions on each island, across urban and agricultural areas, but also in the protected Galápagos national park. When San José marked frogs and attempted to find them in the following 10 days, she could find just one marked frog from time to time, suggesting their populations were enormous. They estimated 6,000 frogs in a single pond. "The calculations are still very low," states the researcher. "I am pretty sure there are even more." Acoustic Chaos and Rising Worries The amphibians' abundance is clear from the acoustic disruption they cause. "The amount of frogs and the sound – it's truly incredible," says the scientist. For the researchers, their nightly vocalizations are helpful in estimating their presence in far-flung areas, using audio devices like the one near San José's workplace. But local farmers say the calls are so raucous they keep them up at night. "During the rainy period, I constantly hear their calls and they're really loud," says a local coffee farmer from Santa Cruz. "At first it was a shock, seeing the first frogs in the region," says the farmer, who started observing their abundance about several years ago when one leaped on her hand as she was stepping out of her front door. Ecological Impact Remains Unknown The sound isn't the primary problem, though. While the species has been in the Galápagos for almost 30 years, scientists still know limited information about its impact on the archipelago's delicately balanced terrestrial and aquatic ecosystems. Scientists are finding out more about the amphibians, including that they can stay as larvae for as long as six months. On archipelagos, it is very typical for invasive species to thrive, as they have none of their enemies. The Galápagos counts over sixteen hundred introduced species, many of which are seriously disrupting the safety of its endemic ones. A 2020 study suggests the non-native amphibians are hungry insect eaters, and might be unevenly eating uncommon insects found exclusively on the archipelago, or depleting the nutrition of the islands' rare birds, disrupting the food chain. Unusual Traits and Control Challenges The island amphibians have shown some atypical characteristics, including surviving in brackish water, which is uncommon for amphibians. Their metamorphosis stage is also extremely variable, with some tadpoles becoming frogs very rapidly and others taking a long time: the researcher witnessed one which remained as a larva in her laboratory for half a year. "We truly don't know this aspect," she says, concerned the tadpoles could be affecting the islands' freshwater, a very scarce resource in Galápagos. More research is needed to determine the optimal way to control the frogs without harming other organisms. Techniques to curb the amphibians in the early 2000s were largely unsuccessful. Park rangers tried collecting large numbers by manual methods and slowly increasing the salinity of ponds in vain. Research indicates applying coffee – which is extremely toxic to amphibians – or using electrocution could help, but these approaches aren't always secure for other uncommon island species. Lacking answers to more of the fundamental issues about their biology and effect, removing the frogs might not even be the correct way to proceed, says the biologist. Financial Obstacles for Research While she expects the growing use of eDNA techniques and DNA analysis will assist her team understand of the invader, funding for the research has been difficult to come by. "Everybody wants to give support for preserving frogs," says San José. "But it's harder to find funding for an introduced frog that you might want to control."