🔗 Share this article

During her daily walk to the scientific station, biologist the researcher stoops near a shallow pond covered by dense plants and retrieves a small green sound device.

She had placed there through the night to capture the distinctive calls of the Fowler's snouted treefrog, recognized by local researchers as an invasive threat with consequences that scientists are starting to comprehend.

Despite teeming with remarkable wildlife – such as centuries-old large turtles, marine iguanas, and the famous finches that sparked Darwin's evolutionary theory – the Galápagos archipelago near the coast of South America had historically been free of frogs and toads.

During the 1990s, this changed. Several small tree frogs made their way from continental Ecuador to the archipelago, likely as hitchhikers on cargo ships.

Genetic studies suggest that, through time, there have been multiple unintentional introductions to the islands, and the amphibians now have a firm presence on two locations: multiple locations.

The population is growing so quickly that scientists have been finding it difficult to keep track, calculating populations in the hundreds of thousands on every island, across urban and agricultural areas, but also in the conservation natural reserve.

When the biologist marked frogs and attempted to find them in the subsequent week and a half, she could locate just one tagged frog occasionally, suggesting their numbers were enormous.

They estimated six thousand frogs in a single pond. "Our estimates are still very conservative," says San José. "I am quite certain there are additional numbers."

Acoustic Chaos and Growing Concerns

The amphibians' proliferation is clear from the sound chaos they create. "The amount of frogs and the sound – it's truly insane," comments the scientist.

For the scientists, their nocturnal mating calls are useful in determining their presence in remote areas, using recorders like the one near the workplace.

But local 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 the island.

"Initially it was a surprise, observing the initial frogs in the region," says Larrea Saltos, who started observing their large numbers about three years ago when one jumped on her hand as she was walking out of her house.

Environmental Consequences Stays Unclear

The sound isn't the primary problem, though. While the amphibians has been in the islands for nearly 30 years, experts still know very little about its impact on the islands' precariously balanced land and water ecosystems.

On islands, it is very common for non-native organisms to prosper, as they have none of their enemies. The islands counts over sixteen hundred introduced types, many of which are significantly disrupting the safety of its native ones.

A 2020 research indicates the invasive amphibians are voracious insect eaters, and might be unevenly consuming rare insects found only on the islands, or depleting the nutrition of the region's uncommon avian species, disrupting the ecosystem balance.

Unique Characteristics and Management Difficulties

The island frogs have exhibited some unusual traits, including surviving in slightly salty water, which is uncommon for amphibians.

Their metamorphosis stage is also highly inconsistent, with some tadpoles becoming frogs very rapidly and others taking a extended period: the researcher witnessed one which remained as a tadpole in her lab for six months.

"We really don't know this aspect," she says, concerned the larvae could be impacting the islands' clean water, a very scarce resource in Galápagos.

Techniques to control the frogs in the early 2000s were mostly unsuccessful. Conservation officers tried capturing large numbers by hand and slowly increasing the salinity of ponds in vain.

Studies indicates applying coffee – which is highly poisonous to frogs – or using electrocution could assist, but these approaches aren't always secure for other uncommon Galápagos organisms.

Without solutions to more of the fundamental issues 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 DNA examination will help her group understand of the invader, financial support for the project has been hard to obtain.

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