The Galápagos Islands Had No Indigenous Amphibians. Then Countless Numbers of Amphibians Made Their Home

During her daily walk to the scientific station, biologist the researcher crouches near a shallow water body surrounded by thick plants and retrieves a compact green sound device.

The device was left there through the night to capture the characteristic calls of the Fowler's snouted treefrog, recognized by Galápagos researchers as an non-native species with effects that experts are just beginning to comprehend.

Although abounding with unique wildlife – such as ancient giant tortoises, marine lizards, and the famous birds that sparked Darwin's theory of evolution – the Galápagos archipelago off the coast of Ecuador had historically been devoid of frogs and toads.

In the late 1990s, this changed. Some tiny amphibians made their way from mainland Ecuador to the islands, probably as stowaways on transport vessels.

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

The population is expanding so rapidly that researchers have been struggling to keep track, calculating populations in the millions on each island, across developed and farming areas, but also in the protected natural reserve.

When San José tagged amphibians and attempted to recapture them in the following 10 days, she could locate only a single marked frog from time to time, indicating their numbers were massive.

They calculated six thousand frogs in a solitary pond. "The calculations are still very conservative," states San José. "I'm pretty sure there are even more."

Deafening Noise and Growing Concerns

The amphibians' proliferation is evident from the sound disruption they cause. "The amount of frogs and the sound – it's really incredible," says San José.

For the researchers, their nightly mating calls are helpful in determining their presence in remote areas, using audio devices like the one outside the office.

But nearby agricultural workers say the calls are so raucous they prevent sleep at night.

"In the wet season, I regularly hear their calls and they're extremely loud," says Jadira Larrea Saltos from Santa Cruz.

"Initially it was a shock, seeing the first frogs in the area," says Larrea Saltos, who started observing 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 fundamental problem, however. While the amphibians has been in the islands for nearly three decades, scientists still know very little about its effect on the archipelago's delicately balanced terrestrial and aquatic ecosystems.

On archipelagos, it is very typical for non-native organisms to thrive, as they have few of their enemies. The Galápagos has over sixteen hundred introduced types, many of which are seriously affecting the safety of its native ones.

A 2020 study suggests the invasive frogs are voracious insect eaters, and might be unevenly consuming rare bugs found only on the archipelago, or depleting the nutrition of the islands' uncommon avian species, affecting the ecosystem balance.

Unique Characteristics and Control Challenges

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

Their metamorphosis process is also extremely inconsistent, with some larvae turning into frogs very rapidly and others taking a extended period: the researcher witnessed one which remained as a tadpole in her lab for half a year.

"We really don't know this part," she says, concerned the tadpoles could be affecting the region's freshwater, a very scarce commodity in the islands.

Methods to curb the frogs in the early 2000s were largely ineffective. Park rangers tried capturing significant quantities by manual methods and slowly increasing the salinity of ponds in vain.

Studies suggests applying coffee – which is highly poisonous to frogs – or using electrical methods could help, but these methods aren't necessarily secure for other uncommon island organisms.

Without answers to more of the basic questions about their biology and impact, culling the frogs might not even be the correct way to proceed, says San José.

Funding Challenges for Study

While she expects the growing use of eDNA techniques and genetic examination will help her team understand of the invasive species, financial support for the research has been difficult to obtain.

"Everybody wants to give support for protecting frogs," says San José. "But it's harder to find funding for an introduced frog that you might want to control."