Galápagos Lacked Any Indigenous Amphibians. Then Countless Numbers of Frogs Made Their Home

On her regular commute to the research facility, scientist Miriam San José crouches near a shallow water body surrounded by dense plants and retrieves a compact green audio recorder.

She had placed there through the night to capture the distinctive calls of the Fowler's snouted treefrog, recognized by local scientists as an non-native species with effects that experts are starting to understand.

Despite abounding with remarkable animals – including centuries-old large turtles, marine iguanas, and the well-known birds that sparked Charles Darwin's theory of evolution – the island chain near the shoreline of Ecuador had long remained free of frogs and toads.

In the late 1990s, this changed. Several small amphibians traveled from mainland the mainland to the islands, likely as stowaways on transport vessels.

DNA studies suggest that, through time, there have been repeated unintentional introductions to the islands, and the amphibians now have a strong foothold on several locations: multiple locations.

The numbers is expanding so quickly that researchers have been finding it difficult to monitor, calculating populations in the hundreds of thousands on every island, across urban and farming areas, but also in the protected Galápagos national park.

When San José marked amphibians and attempted to recapture them in the subsequent 10 days, she could find just one tagged frog from time to time, indicating their populations were enormous.

They calculated six thousand frogs in a single pond. "The calculations are still very conservative," states the researcher. "I am quite certain there are additional numbers."

Acoustic Chaos and Growing Concerns

The frogs' abundance is evident from the acoustic disruption they create. "The number of frogs and the sound – it's really insane," comments San José.

For the scientists, their nocturnal mating calls are useful in determining their existence in far-flung areas, using recorders like the one near San José's workplace.

But local farmers say the calls are so loud they keep them up at night.

"During the rainy period, I constantly hear their calls and they're extremely loud," says Jadira Larrea Saltos from Santa Cruz.

"At first it was a surprise, seeing the first frogs in the area," says the farmer, who started observing their abundance about three years ago when one leaped on her hand as she was walking out of her house.

Ecological Impact Remains Unknown

The sound isn't the fundamental problem, though. While the species has been in the Galápagos for almost 30 years, experts still know very little about its impact on the islands' precariously balanced terrestrial and aquatic ecosystems.

On archipelagos, it is very common for invasive organisms to prosper, as they have none of their enemies. The islands has over sixteen hundred invasive species, many of which are seriously affecting the safety of its endemic ones.

A recent research suggests the non-native amphibians are voracious insect consumers, and might be disproportionately consuming uncommon insects found exclusively on the archipelago, or depleting the food sources of the region's rare avian species, disrupting the ecosystem balance.

Unusual Traits and Control Challenges

The island amphibians have exhibited some atypical characteristics, including living in brackish water, which is uncommon for amphibians.

Their development process is also extremely inconsistent, with some tadpoles turning into frogs very rapidly and others taking a extended period: San José observed one which remained as a tadpole in her laboratory for half a year.

"We truly don't know this part," she says, worried the tadpoles could be affecting the islands' freshwater, a very scarce commodity in Galápagos.

Methods to control the frogs in the early 2000s were mostly unsuccessful. Park rangers tried capturing large numbers by manual methods and slowly raising the salinity of ponds in vain.

Research indicates spraying coffee – which is extremely poisonous to amphibians – or using electrical methods could help, but these approaches aren't necessarily secure for other rare Galápagos organisms.

Lacking answers to more of the basic issues about their biology and impact, culling the frogs might not even be the correct way to proceed, says the biologist.

Funding Challenges for Study

While she expects the growing use of eDNA techniques and DNA examination will help her team make sense of the invader, financial support for the research has been hard to come by.

"Everyone wants to give funding for preserving frogs," says San José. "But it's more difficult to find financial backing for an introduced frog that you might want to control."