🔗 Share this article

On her daily commute to the research facility, scientist the researcher crouches near a small pond covered by dense plants and collects a small green sound device.

She had placed there overnight to capture the characteristic calls of the Scinax quinquefasciatus, recognized by local scientists as an non-native species with effects that scientists are starting to comprehend.

Despite teeming with unique wildlife – including ancient large turtles, swimming iguanas, and the well-known birds that inspired Darwin's evolutionary theory – the Galápagos archipelago off the shoreline of South America had historically been devoid of frogs and toads.

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

DNA studies suggest that, through time, there have been repeated accidental introductions to the archipelago, and the frogs now have a firm foothold on two locations: multiple locations.

The numbers is growing so quickly that researchers have been struggling to monitor, estimating populations in the millions on each island, across developed and farming areas, but also in the protected Galápagos national park.

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

They estimated six thousand frogs in a single pond. "The calculations are still very low," states San José. "I'm pretty sure there are additional numbers."

Acoustic Chaos and Rising Worries

The amphibians' proliferation is evident from the acoustic chaos they cause. "The number of frogs and the sound – it's truly incredible," comments San José.

For the scientists, their nightly mating calls are useful in determining their presence in remote areas, using audio devices like the one outside San José's office.

But nearby agricultural workers say the sounds are so loud they prevent sleep at night.

"During the wet season, I constantly hear their croaks and they're extremely loud," says Jadira Larrea Saltos from the island.

"Initially it was a surprise, seeing the initial frogs in the area," says the farmer, who started observing their large numbers about three years ago when one leaped on her palm as she was stepping out of her front door.

Ecological Impact Remains Unclear

The noise isn't the primary problem, though. While the amphibians has been in the islands for nearly three decades, scientists still know limited information about its effect on the archipelago's delicately balanced terrestrial and aquatic ecosystems.

On archipelagos, it is very common for non-native organisms to thrive, as they have few of their enemies. The islands counts 1,645 introduced species, many of which are seriously disrupting the survival of its native ones.

A recent study indicates the invasive amphibians are voracious insect consumers, and might be disproportionately consuming uncommon bugs found exclusively on the islands, or reducing the nutrition of the islands' uncommon avian species, affecting the ecosystem balance.

Unusual Traits and Management Difficulties

The island frogs have exhibited some unusual traits, including surviving in brackish water, which is rare for frogs.

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

"We really don't know this aspect," she says, concerned the larvae could be impacting the region's freshwater, a very limited resource in Galápagos.

Methods to control the amphibians in the early 2000s were mostly unsuccessful. Park rangers tried capturing significant quantities by manual methods and slowly raising the salt content of lagoons in without success.

Studies suggests spraying coffee – which is extremely toxic to amphibians – or using electrocution could help, but these approaches aren't always safe for other uncommon Galápagos species.

Lacking answers to more of the fundamental issues about their lifestyle and impact, removing the amphibians might not even be the right way to advance, says San José.

Funding Challenges for Study

While she hopes the growing use of environmental DNA techniques and DNA examination will help her team understand of the invader, funding for the project has been hard to obtain.

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