The Galápagos Islands Had No Native Amphibians. Then Countless Numbers of Amphibians Made Their Home
On her regular commute to the scientific station, biologist the researcher crouches near a small water body surrounded by thick vegetation and collects a small plastic audio device.
She had placed there through the night to capture the distinctive croaks of the Scinax quinquefasciatus, known by Galápagos scientists as an invasive threat with consequences that scientists are just beginning to understand.
Although abounding with remarkable animals – including 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 devoid of frogs and toads.
During the 1990s, this changed. Several tiny amphibians traveled from mainland Ecuador to the archipelago, likely as hitchhikers on transport vessels.
DNA research suggest that, through time, there have been repeated accidental arrivals to the archipelago, and the amphibians now have a strong foothold on several islands: multiple locations.
The numbers is growing so rapidly that scientists have been struggling to monitor, estimating numbers in the hundreds of thousands on each island, across developed and agricultural areas, but also in the conservation Galápagos national park.
When San José tagged amphibians and attempted to find them in the subsequent 10 days, she could find only a single marked frog from time to time, suggesting their populations were massive.
They calculated six thousand frogs in a single pond. "Our estimates are still very low," states the researcher. "I'm pretty sure there are even more."
Acoustic Chaos and Growing Concerns
The frogs' proliferation is clear from the sound chaos they create. "The amount of frogs and the noise – it's really insane," comments San José.
For the researchers, their nightly mating calls are helpful in determining their existence in far-flung areas, using audio devices like the one near the workplace.
But local farmers say the sounds are so loud they prevent sleep at night.
"In the wet season, I regularly hear their croaks and they're extremely loud," says a local coffee farmer from Santa Cruz.
"At first it was a shock, observing the first frogs in the region," says Larrea Saltos, who started observing their abundance about several years ago when one leaped on her palm as she was walking out of her house.
Ecological Impact Remains Unknown
The noise isn't the fundamental problem, though. While the amphibians has been in the Galápagos for almost 30 years, scientists still know very little about its effect on the islands' precariously balanced terrestrial and aquatic ecosystems.
On islands, it is very typical for non-native species to prosper, as they have few of their enemies. The Galápagos has over sixteen hundred introduced types, many of which are seriously affecting the survival of its endemic ones.
A recent study indicates the non-native frogs are hungry insect eaters, and might be unevenly eating rare insects found exclusively on the islands, or depleting the nutrition of the region's rare birds, affecting the ecosystem balance.
Unique Characteristics and Control Challenges
The Galápagos frogs have shown some atypical traits, including surviving in slightly salty water, which is uncommon for frogs.
Their metamorphosis process is also highly inconsistent, with some tadpoles becoming frogs very rapidly and others taking a extended period: San José observed one which remained as a tadpole in her lab for six months.
"We truly don't know this part," she says, concerned the larvae could be affecting the islands' freshwater, a very scarce commodity in the islands.
Methods to control the frogs in the beginning of the century were largely ineffective. Conservation officers tried collecting 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 electrocution could help, but these approaches aren't always safe for other rare Galápagos organisms.
Lacking solutions to more of the basic questions about their biology and impact, culling the amphibians might not even be the right way to proceed, says San José.
Funding Challenges for Research
While she hopes the increasing use of eDNA methods and genetic examination will help her group understand of the invasive species, financial support for the project has been hard to come by.
"Everybody wants to give support 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."
