🔗 Share this article

On her regular commute to the scientific station, scientist the researcher stoops near a small water body covered by thick plants and retrieves a small plastic sound recorder.

The device was left there overnight to record the characteristic croaks of the Scinax quinquefasciatus, known by Galápagos researchers as an invasive threat with effects that experts are starting to understand.

Despite abounding with remarkable animals – such as centuries-old large turtles, marine iguanas, and the famous finches that sparked Darwin's theory of evolution – the island chain near the coast of Ecuador had historically been devoid of amphibians.

In the late 1990s, this changed. Several small tree frogs traveled from continental the mainland to the archipelago, probably as stowaways on transport vessels.

Genetic studies suggest that, over the years, there have been repeated accidental introductions to the archipelago, and the amphibians now have a strong presence on two locations: Isabela and Santa Cruz.

The population is expanding so quickly that researchers have been struggling to monitor, estimating numbers in the millions on each island, across urban and farming areas, but also in the conservation Galápagos national park.

When San José marked frogs and attempted to find them in the subsequent 10 days, she could find only a single tagged frog from time to time, indicating their populations were enormous.

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

Acoustic Chaos and Rising Worries

The frogs' proliferation is evident from the acoustic disruption they create. "The number of frogs and the sound – it's really insane," says San José.

For the scientists, their nocturnal mating calls are helpful in determining their existence in remote areas, using recorders like the one near San José's workplace.

But nearby agricultural workers say the calls are so raucous they keep them up at night.

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

"At first it was a surprise, seeing the initial frogs in the region," says Larrea Saltos, who started noticing their abundance about three years ago when one jumped on her hand as she was walking out of her house.

Ecological Impact Stays Unclear

The sound isn't the primary problem, though. While the amphibians has been in the islands for nearly three decades, scientists still know very little about its impact on the islands' delicately balanced terrestrial and aquatic environments.

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

A recent research indicates the non-native amphibians are voracious insect eaters, and might be unevenly consuming uncommon bugs found only 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 atypical characteristics, including surviving in slightly salty water, which is uncommon for amphibians.

Their metamorphosis stage is also highly variable, with some tadpoles turning into frogs very quickly and others taking a long time: the researcher observed 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 affecting the islands' clean water, a very scarce resource in the islands.

Methods to control the frogs in the early 2000s were largely ineffective. Park rangers tried capturing significant quantities by hand and slowly raising the salinity of lagoons in vain.

Studies suggests spraying caffeine – which is highly toxic to amphibians – or using electrical methods could assist, but these methods aren't necessarily safe for other uncommon Galápagos species.

Without solutions to more of the basic questions about their biology and effect, removing the amphibians might not even be the correct way to advance, says San José.

Financial Obstacles for Study

While she expects the increasing use of eDNA methods and DNA analysis will assist her group make sense of the invasive species, funding for the research has been hard to come by.

"Everybody wants to give funding for preserving frogs," says San José. "But it's more difficult to find financial backing for an invasive frog that you might want to control."