🔗 Share this article The Galápagos Islands Had No Indigenous Amphibians. Then Countless Numbers of Frogs Arrived During her daily walk to the scientific station, biologist Miriam San José crouches near a small water body covered by thick plants and retrieves a small plastic audio recorder. The device was left there through the night to record the distinctive croaks of the Fowler's snouted treefrog, recognized by local researchers as an invasive threat with consequences that experts are starting to comprehend. Despite abounding with unique wildlife – including ancient giant tortoises, swimming iguanas, and the well-known birds that inspired Charles Darwin's evolutionary theory – the Galápagos archipelago near the coast of South America had long remained devoid of amphibians. In the late 1990s, this changed. Several small tree frogs traveled from continental the mainland to the islands, probably as stowaways on transport vessels. The invasive species arrived in the 1990s and have become established on multiple Galápagos islands. DNA studies suggest that, through time, there have been multiple accidental introductions to the islands, and the amphibians now have a strong presence on two islands: multiple locations. The population is growing so quickly that researchers have been struggling to keep track, estimating populations in the millions on each island, across developed and farming areas, but also in the conservation Galápagos national park. When San José marked amphibians and attempted to find them in the following 10 days, she could find only a single marked frog occasionally, suggesting their populations were enormous. They calculated 6,000 frogs in a solitary pond. "Our estimates are still very conservative," states San José. "I'm pretty sure there are even more." Acoustic Chaos and Growing Concerns The amphibians' abundance is evident from the acoustic disruption they create. "The number of frogs and the sound – it's truly insane," says the scientist. For the researchers, their nightly mating calls are helpful in determining their existence in remote areas, using audio devices like the one outside the office. But local agricultural workers say the calls are so loud they keep them up at night. "In the wet season, I constantly hear their croaks and they're really loud," says a local coffee farmer from the island. "At first it was a shock, observing the first frogs in the region," says Larrea Saltos, who started noticing their large numbers about several years ago when one leaped on her palm as she was stepping out of her front door. Ecological Impact Remains Unknown The noise isn't the fundamental problem, though. While the species has been in the Galápagos for almost three decades, experts still know limited information about its effect on the islands' delicately balanced land and water ecosystems. Researchers are discovering more about the amphibians, including that they can stay as tadpoles for as long as six months. On archipelagos, it is very common for invasive species to prosper, as they have few of their natural predators. The islands counts over sixteen hundred introduced species, many of which are seriously affecting the safety of its native ones. A recent study indicates the invasive amphibians are hungry insect eaters, and might be unevenly eating rare bugs found only on the archipelago, or reducing the nutrition of the islands' rare avian species, affecting the ecosystem balance. Unusual Traits and Control Challenges The Galápagos frogs have shown some unusual traits, including surviving in brackish water, which is rare for amphibians. Their metamorphosis stage is also highly inconsistent, with some tadpoles becoming frogs very rapidly and others taking a extended period: San José observed one which remained as a larva in her laboratory for half a year. "We truly don't know this part," she says, worried the larvae could be impacting the islands' freshwater, a very limited resource in Galápagos. Additional studies is required to determine the best way to control the frogs without affecting other organisms. Methods to control the frogs in the beginning of the century were mostly ineffective. Park rangers tried collecting large numbers by manual methods and slowly increasing the salinity of lagoons in vain. Studies indicates applying coffee – which is extremely poisonous to amphibians – or using electrocution could help, but these approaches aren't necessarily secure for other uncommon Galápagos species. Lacking answers to more of the basic questions about their biology and impact, culling the frogs might not even be the correct way to advance, says San José. Financial Obstacles for Research While she expects the growing use of environmental DNA methods and DNA examination will help her group understand of the invader, funding for the project has been difficult to obtain. "Everybody wants to give support for preserving frogs," says San José. "But it's harder to find financial backing for an invasive frog that you might want to manage."