Galápagos Had No Native Amphibians. Then Hundreds of Thousands of Frogs Arrived

During her regular commute to the research facility, scientist Miriam San José crouches near a shallow pond covered by thick vegetation and collects a compact plastic sound recorder.

The device was left there through the night to capture the distinctive calls of the Scinax quinquefasciatus, recognized by Galápagos researchers as an invasive threat with effects that scientists are starting to comprehend.

Although abounding with unique wildlife – including ancient giant tortoises, marine iguanas, and the famous birds that inspired Darwin's theory of evolution – the Galápagos archipelago near the coast of Ecuador had historically been free of amphibians.

In the late 1990s, this shifted. Several tiny amphibians traveled from continental the mainland to the islands, likely as hitchhikers on transport vessels.

Genetic studies indicate that, over the years, there have been multiple unintentional introductions to the islands, and the frogs now have a strong foothold on several islands: multiple locations.

The numbers is growing so rapidly that scientists have been struggling to monitor, estimating populations in the hundreds of thousands on every island, across developed and farming areas, but also in the conservation Galápagos national park.

When the biologist tagged frogs and attempted to find them in the subsequent 10 days, she could find only a single marked frog from time to time, suggesting their populations were massive.

They estimated six thousand frogs in a solitary pond. "The calculations are still very low," states the researcher. "I am quite certain there are even more."

Acoustic Chaos and Rising Worries

The amphibians' abundance is clear from the acoustic chaos they create. "The number of frogs and the sound – it's truly insane," says the scientist.

For the researchers, their nocturnal vocalizations are helpful in estimating their existence in far-flung areas, using audio devices like the one near the office.

But nearby farmers say the sounds are so raucous they prevent sleep at night.

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

"At first it was a surprise, seeing the first frogs in the region," says Larrea Saltos, who started observing their abundance about several years ago when one leaped on her hand as she was walking out of her front door.

Environmental Consequences Stays Unclear

The noise isn't the fundamental problem, however. While the amphibians has been in the Galápagos for nearly three decades, experts still know very little about its impact on the archipelago's delicately balanced terrestrial and aquatic ecosystems.

On islands, it is very typical for non-native species to prosper, as they have none of their natural predators. The Galápagos counts over sixteen hundred introduced types, many of which are seriously affecting the survival of its native ones.

A 2020 research suggests the non-native frogs are voracious insect eaters, and might be disproportionately consuming rare insects found exclusively on the archipelago, or reducing the nutrition of the region's uncommon avian species, affecting the ecosystem balance.

Unique Characteristics and Management Difficulties

The Galápagos amphibians have shown some unusual characteristics, including living in slightly salty water, which is rare for amphibians.

Their development stage is also extremely variable, with some tadpoles becoming frogs very quickly and others taking a extended period: the researcher witnessed one which remained as a larva in her lab for six months.

"We truly don't know this aspect," she says, worried the tadpoles could be impacting the islands' clean water, a very limited commodity in Galápagos.

Techniques to control the amphibians in the beginning of the century were largely ineffective. Conservation officers tried capturing large numbers by manual methods and slowly raising the salinity of lagoons in without success.

Research suggests applying caffeine – which is highly toxic to frogs – or using electrocution could assist, but these methods aren't always safe for other rare island organisms.

Without solutions to more of the basic questions about their lifestyle and effect, removing the frogs might not even be the correct way to proceed, says San José.

Financial Obstacles for Research

While she expects the growing use of environmental DNA methods and genetic examination will assist her group make sense of the invader, funding for the research has been difficult to come by.

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