🔗 Share this article

During her regular commute to the scientific station, biologist Miriam San José crouches near a small water body covered by dense plants and collects a small green audio device.

The device was left there through the night to capture the distinctive croaks of the Scinax quinquefasciatus, recognized by local researchers as an non-native threat with effects that scientists are just beginning to comprehend.

Although abounding with unique animals – such as ancient large turtles, swimming lizards, and the famous finches that inspired Charles Darwin's theory of evolution – the Galápagos archipelago off the shoreline of Ecuador had historically been free of amphibians.

In the late 1990s, this shifted. Some small amphibians made their way from mainland the mainland to the archipelago, probably as stowaways on cargo ships.

DNA studies indicate that, over the years, there have been repeated accidental introductions to the archipelago, and the amphibians now have a strong foothold on two islands: multiple locations.

The numbers is growing so rapidly that researchers have been struggling to keep track, calculating numbers 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 following week and a half, she could find just one tagged frog from time to time, indicating their numbers were massive.

They calculated 6,000 frogs in a single pond. "Our estimates are still very conservative," states San José. "I'm quite certain there are even more."

Acoustic Chaos and Growing Concerns

The amphibians' abundance is evident from the acoustic disruption they create. "The amount of frogs and the noise – it's truly incredible," says the scientist.

For the scientists, their nightly vocalizations are helpful in determining their existence in far-flung areas, using recorders like the one outside San José's office.

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

"In the rainy period, I constantly hear their calls and they're really loud," says Jadira Larrea Saltos from the island.

"At first it was a shock, seeing the first frogs in the area," says the farmer, who started noticing their abundance about several years ago when one jumped on her hand as she was stepping out of her front door.

Ecological Impact Remains Unknown

The sound isn't the primary problem, however. While the amphibians has been in the Galápagos for nearly three decades, experts still know very little about its effect on the islands' precariously balanced land and water ecosystems.

On archipelagos, it is very common for invasive organisms to thrive, as they have few of their enemies. The Galápagos has over sixteen hundred introduced species, many of which are seriously disrupting the survival of its endemic ones.

A recent research indicates the non-native frogs are voracious insect eaters, and might be disproportionately consuming rare bugs found exclusively on the islands, or reducing the food sources of the region's uncommon avian species, affecting the ecosystem balance.

Unique Characteristics and Control Challenges

The Galápagos amphibians have shown some atypical traits, including living in brackish water, which is uncommon for frogs.

Their metamorphosis stage is also extremely inconsistent, with some larvae becoming frogs very rapidly and others taking a extended period: San José observed one which stayed as a larva in her laboratory for half a year.

"We really don't know this part," she says, worried the larvae could be affecting the region's freshwater, a very limited commodity in Galápagos.

Techniques to control the frogs in the early 2000s were largely unsuccessful. Park rangers tried capturing significant quantities by manual methods and slowly increasing the salt content of ponds in vain.

Studies indicates applying caffeine – which is highly poisonous to amphibians – or using electrocution could help, but these methods aren't always safe for other rare Galápagos organisms.

Lacking solutions to more of the fundamental questions about their biology and effect, removing the amphibians might not even be the correct way to proceed, says the biologist.

Financial Obstacles for Study

While she hopes the increasing use of eDNA techniques and genetic examination will help her team make sense of the invasive species, financial support for the project has been hard to come by.

"Everybody wants to give funding for protecting frogs," says the researcher. "But it's harder to find funding for an invasive frog that you might want to manage."