The Galápagos Islands Lacked Any Indigenous Amphibians. Until Countless Numbers of Frogs Arrived

On her regular walk to the research facility, biologist Miriam San José stoops near a shallow water body surrounded by dense vegetation and retrieves a compact plastic audio recorder.

She had placed there through the night to capture the characteristic croaks of the Scinax quinquefasciatus, recognized by local scientists as an non-native species with effects that experts are just beginning to understand.

Despite abounding with remarkable animals – such as ancient large turtles, swimming iguanas, and the well-known birds that sparked Charles Darwin's evolutionary theory – the Galápagos archipelago off the coast of Ecuador had historically been free of amphibians.

In the late 1990s, this shifted. Several tiny amphibians made their way from mainland the mainland to the islands, probably as stowaways on transport vessels.

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

The population is expanding so quickly that researchers have been struggling to keep track, estimating numbers in the hundreds of thousands on every island, across developed and farming areas, but also in the protected Galápagos national park.

When the biologist marked amphibians and attempted to recapture them in the subsequent week and a half, she could locate only a single tagged frog occasionally, suggesting their populations were massive.

They estimated 6,000 frogs in a solitary pond. "The calculations are still very low," says the researcher. "I am quite certain there are even more."

Acoustic Chaos and Growing Concerns

The amphibians' abundance is clear from the acoustic chaos they cause. "The amount of frogs and the noise – it's truly incredible," comments San José.

For the scientists, their nightly vocalizations are useful in determining their presence in remote areas, using recorders like the one near the office.

But local agricultural workers say the calls are so loud they keep them up at night.

"During the wet season, I regularly hear their calls and they're extremely loud," says a local coffee farmer from Santa Cruz.

"At first it was a surprise, seeing the initial frogs in the area," says Larrea Saltos, who started observing their large numbers about several years ago when one jumped on her palm as she was stepping out of her front door.

Environmental Consequences Remains Unclear

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

On islands, it is very common for invasive organisms to prosper, as they have none of their enemies. The Galápagos counts 1,645 invasive types, many of which are significantly affecting the safety of its endemic ones.

A recent study suggests the invasive frogs are hungry insect consumers, and might be unevenly consuming rare insects found only on the islands, or reducing the food sources of the region's uncommon avian species, disrupting the ecosystem balance.

Unique Characteristics and Management Difficulties

The Galápagos frogs have exhibited some unusual characteristics, including living in slightly salty water, which is uncommon for amphibians.

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

"We really don't know this part," she says, concerned the tadpoles could be affecting the region's freshwater, a very limited commodity in the islands.

Methods to curb the frogs in the early 2000s were mostly ineffective. Conservation officers tried capturing large numbers by manual methods and slowly increasing the salinity of ponds in without success.

Research indicates applying caffeine – which is extremely toxic to amphibians – or using electrocution could help, but these approaches aren't always secure for other rare Galápagos organisms.

Without answers to more of the fundamental issues about their biology and impact, removing the amphibians might not even be the correct way to proceed, says San José.

Financial Obstacles for Research

While she hopes the growing use of environmental DNA techniques and genetic analysis will help her team make sense of the invasive species, funding for the project has been hard to come by.

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