Galápagos Lacked Any Indigenous Amphibians. Then Hundreds of Thousands of Amphibians Arrived

During her daily commute to the scientific station, biologist Miriam San José stoops near a small water body surrounded by dense plants and retrieves a small plastic audio device.

The device was left there through the night to record the characteristic croaks of the Scinax quinquefasciatus, known by Galápagos scientists as an non-native species with effects that experts are starting to understand.

Although teeming with remarkable wildlife – such as ancient large turtles, swimming lizards, and the famous finches that inspired Darwin's evolutionary theory – the island chain off the coast of Ecuador had long remained devoid of amphibians.

In the late 1990s, this changed. Some tiny tree frogs traveled from continental the mainland to the archipelago, likely as stowaways on cargo ships.

DNA research suggest that, over the years, there have been multiple accidental arrivals to the archipelago, and the frogs now have a firm foothold on two islands: Isabela and Santa Cruz.

The population is expanding so quickly that researchers have been struggling to monitor, calculating populations in the hundreds of thousands on each island, across urban and agricultural areas, but also in the conservation natural reserve.

When San José marked amphibians and attempted to find them in the subsequent 10 days, she could locate only a single marked frog occasionally, indicating their numbers were enormous.

They calculated six thousand frogs in a single pond. "The calculations are still very conservative," states the researcher. "I'm quite certain there are even more."

Acoustic Chaos and Rising Worries

The frogs' proliferation is evident from the acoustic disruption they cause. "The amount of frogs and the noise – it's really insane," comments the scientist.

For the researchers, their nocturnal vocalizations are helpful in estimating their presence in remote areas, using audio devices like the one near San José's office.

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

"During the rainy period, I regularly hear their croaks and they're really loud," says a local coffee farmer from the island.

"Initially it was a surprise, observing the first frogs in the area," says the farmer, who started noticing their abundance about three years ago when one jumped on her palm as she was walking out of her house.

Environmental Consequences Remains Unclear

The noise isn't the primary problem, though. While the species has been in the Galápagos for almost 30 years, experts still know limited information about its effect on the archipelago's delicately balanced terrestrial and aquatic ecosystems.

On archipelagos, it is very common for invasive species to thrive, as they have none of their enemies. The islands counts 1,645 invasive species, many of which are significantly disrupting the survival of its native ones.

A 2020 research suggests the invasive frogs are hungry bug consumers, and might be disproportionately eating rare insects found exclusively on the islands, or depleting the nutrition of the islands' uncommon avian species, disrupting the ecosystem balance.

Unique Characteristics and Control Challenges

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

Their metamorphosis process is also extremely variable, with some larvae becoming frogs very rapidly and others taking a extended period: San José observed one which stayed as a larva in her laboratory 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 commodity in the islands.

Methods to curb the frogs in the early 2000s were largely unsuccessful. Conservation officers tried capturing large numbers by manual methods and slowly increasing the salinity of lagoons in vain.

Studies indicates applying coffee – which is highly toxic to amphibians – or using electrocution could assist, but these methods aren't always secure for other uncommon island organisms.

Lacking solutions to more of the fundamental questions about their biology and effect, culling the amphibians might not even be the right way to proceed, says San José.

Financial Obstacles for Research

While she expects the increasing use of environmental DNA methods and genetic analysis will assist her group understand of the invasive species, funding 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 financial backing for an invasive frog that you might want to control."