🔗 Share this article

On her daily commute to the scientific station, scientist Miriam San José crouches near a shallow pond surrounded by dense vegetation and retrieves a compact green sound recorder.

She had placed there through the night to record the distinctive calls of the Scinax quinquefasciatus, recognized by Galápagos scientists as an invasive species with effects that experts are just beginning to comprehend.

Despite teeming with unique animals – such as centuries-old giant tortoises, marine lizards, and the well-known finches that inspired Darwin's evolutionary theory – the island chain near the coast of Ecuador had long remained free of frogs and toads.

During the 1990s, this changed. Some tiny tree frogs made their way from mainland Ecuador to the islands, likely as stowaways on transport vessels.

DNA studies indicate that, over the years, there have been repeated accidental arrivals to the islands, and the amphibians now have a firm presence on two islands: multiple locations.

The numbers is growing so rapidly that researchers have been struggling to monitor, estimating numbers in the hundreds of thousands on each island, across developed and agricultural areas, but also in the protected natural reserve.

When San José marked amphibians and attempted to find them in the subsequent week and a half, she could locate just one marked frog from time to time, indicating their populations were enormous.

They calculated 6,000 frogs in a single pond. "The calculations are still very conservative," says the researcher. "I'm pretty sure there are additional numbers."

Deafening Noise and Rising Worries

The frogs' proliferation is clear from the acoustic disruption they cause. "The number of frogs and the sound – it's really insane," comments the scientist.

For the researchers, their nocturnal mating calls are helpful in determining their existence in remote areas, using recorders like the one outside the office.

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

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

"Initially it was a shock, observing the initial frogs in the region," says the farmer, who started noticing their large numbers about three years ago when one jumped on her palm as she was stepping out of her house.

Ecological Impact Remains Unclear

The noise isn't the fundamental problem, however. While the amphibians has been in the islands for nearly three decades, experts still know very little about its impact on the islands' precariously balanced terrestrial and aquatic environments.

On archipelagos, it is very common for non-native species to thrive, as they have few of their natural predators. The islands has over sixteen hundred introduced species, many of which are significantly affecting the safety of its endemic ones.

A recent research suggests the non-native frogs are voracious insect eaters, and might be unevenly consuming rare insects found exclusively on the archipelago, or depleting the nutrition of the islands' rare avian species, disrupting the ecosystem balance.

Unique Characteristics and Control Challenges

The island amphibians have shown some unusual characteristics, including living in slightly salty water, which is rare for amphibians.

Their metamorphosis process is also highly inconsistent, with some larvae becoming frogs very quickly and others taking a long time: the researcher observed one which remained as a larva in her lab for half a year.

"We really don't know this part," she says, worried the tadpoles could be impacting the region's clean water, a very limited resource in Galápagos.

Techniques to curb the amphibians in the early 2000s were largely ineffective. Park rangers tried collecting large numbers by manual methods and slowly increasing the salt content of lagoons in vain.

Research suggests spraying coffee – which is extremely toxic to amphibians – or using electrical methods could help, but these approaches aren't always safe for other rare Galápagos organisms.

Lacking answers to more of the basic questions about their biology and impact, removing the frogs might not even be the correct way to advance, says San José.

Financial Obstacles for Research

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

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