Galápagos Had No Native Amphibians. Until Hundreds of Thousands of Amphibians Made Their Home

During her daily commute to the research facility, scientist Miriam San José crouches near a small water body covered by dense vegetation and collects a compact green audio device.

The device was left there overnight to record the distinctive croaks of the Scinax quinquefasciatus, recognized by Galápagos scientists as an non-native threat with effects that scientists are just beginning to comprehend.

Despite abounding with remarkable wildlife – such as ancient large turtles, swimming iguanas, and the well-known birds that inspired Darwin's evolutionary theory – the Galápagos archipelago off the shoreline of Ecuador had long remained devoid of amphibians.

In the late 1990s, this changed. Several small amphibians made their way from mainland the mainland to the islands, probably as hitchhikers on transport vessels.

Genetic studies suggest that, through time, 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 expanding so rapidly that scientists have been finding it difficult to keep track, estimating populations in the hundreds of thousands on every island, across developed and agricultural areas, but also in the protected Galápagos national park.

When San José tagged frogs and attempted to recapture them in the following week and a half, she could find only a single tagged frog from time to time, indicating their populations were massive.

They calculated 6,000 frogs in a single pond. "The calculations are still very low," says San José. "I'm pretty sure there are additional numbers."

Acoustic Chaos and Rising Worries

The frogs' proliferation is evident from the acoustic disruption they cause. "The number of frogs and the noise – it's truly incredible," says San José.

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

But nearby farmers say the calls are so loud they prevent sleep at night.

"In the rainy period, I constantly 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 region," says the farmer, who started observing their large numbers about three years ago when one leaped on her hand as she was stepping out of her front door.

Ecological Impact Remains Unknown

The noise isn't the fundamental problem, though. While the amphibians has been in the Galápagos for almost three decades, scientists still know very little about its effect on the islands' delicately balanced land and water environments.

On archipelagos, it is very common for invasive organisms to prosper, as they have few of their natural predators. The islands counts 1,645 invasive species, many of which are significantly disrupting the safety of its native ones.

A recent study indicates the non-native amphibians are voracious insect eaters, and might be disproportionately eating uncommon bugs found exclusively on the archipelago, or depleting the nutrition of the region's rare avian species, disrupting the ecosystem balance.

Unusual Traits and Management Difficulties

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

Their metamorphosis stage is also highly variable, with some tadpoles turning into frogs very rapidly and others taking a long time: the researcher witnessed 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 affecting the islands' freshwater, a very limited resource in Galápagos.

Techniques to curb the amphibians in the early 2000s were mostly unsuccessful. Conservation officers tried capturing significant quantities by manual methods and gradually raising the salt content of ponds in vain.

Research indicates spraying caffeine – which is extremely poisonous to frogs – or using electrocution could help, but these methods aren't necessarily secure for other rare Galápagos species.

Without answers to more of the basic questions about their lifestyle and impact, removing the frogs might not even be the correct way to advance, says the biologist.

Financial Obstacles for Research

While she expects the growing use of eDNA methods and genetic examination will assist her team make sense of the invasive species, financial support for the research has been hard to come by.

"Everybody wants to give support for protecting frogs," says the researcher. "But it's more difficult to find financial backing for an introduced frog that you might want to manage."