Galápagos Had No Indigenous Amphibians. Until Countless Numbers of Frogs Invaded

On her daily walk to the research facility, biologist the researcher crouches near a shallow water body covered by thick vegetation and collects a small plastic audio recorder.

She had placed there through the night to capture the characteristic croaks of the Fowler's snouted treefrog, recognized by local scientists as an non-native species with effects that scientists are starting to comprehend.

Despite teeming with unique animals – such as centuries-old giant tortoises, marine lizards, and the famous birds that inspired Charles Darwin's evolutionary theory – the island chain off the coast of Ecuador had long remained devoid of amphibians.

During the 1990s, this shifted. Several tiny amphibians traveled from continental the mainland to the archipelago, probably as stowaways on transport vessels.

DNA studies indicate that, over the years, there have been repeated unintentional introductions to the archipelago, and the frogs now have a strong presence on two islands: Isabela and Santa Cruz.

The numbers is growing so rapidly that scientists have been struggling to monitor, calculating numbers in the hundreds of thousands on each island, across urban and farming areas, but also in the conservation Galápagos national park.

When the biologist marked frogs and attempted to find them in the following week and a half, she could locate only a single marked frog occasionally, suggesting their numbers were massive.

They calculated six thousand frogs in a single pond. "Our estimates are still very conservative," states San José. "I am quite certain there are additional numbers."

Deafening Noise and Rising Worries

The amphibians' abundance is evident from the acoustic disruption they cause. "The amount of frogs and the noise – it's truly insane," says San José.

For the scientists, their nocturnal vocalizations are helpful in determining their presence in far-flung areas, using audio devices like the one near the office.

But local farmers say the sounds are so loud they keep them up at night.

"During the rainy period, I regularly hear their calls and they're extremely loud," says Jadira Larrea Saltos from the island.

"Initially it was a shock, seeing the initial frogs in the area," says Larrea Saltos, who started noticing their large numbers about several years ago when one jumped on her hand as she was stepping out of her house.

Environmental Consequences Stays Unknown

The noise isn't the primary problem, however. While the amphibians has been in the islands for almost three decades, experts still know limited information about its effect on the islands' precariously balanced terrestrial and aquatic ecosystems.

On islands, it is very typical for invasive organisms to prosper, as they have none of their natural predators. The islands counts 1,645 invasive species, many of which are seriously affecting the safety of its native ones.

A recent research suggests the invasive amphibians are hungry insect consumers, and might be unevenly eating rare insects found exclusively on the archipelago, or reducing the food sources of the region's uncommon birds, affecting the ecosystem balance.

Unusual Traits and Management Difficulties

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

Their development stage is also extremely variable, with some larvae becoming frogs very rapidly and others taking a long time: the researcher observed one which stayed as a larva in her laboratory for six months.

"We truly don't know this aspect," she says, concerned the larvae could be impacting the region's freshwater, a very limited resource in the islands.

Techniques to control the frogs in the early 2000s were mostly ineffective. Park rangers tried collecting significant quantities by manual methods and gradually increasing the salt content of ponds in without success.

Studies indicates spraying coffee – which is extremely poisonous to frogs – or using electrical methods could help, but these approaches aren't necessarily safe for other rare island organisms.

Lacking solutions to more of the fundamental issues about their biology and effect, removing the frogs might not even be the right way to advance, says San José.

Financial Obstacles for Study

While she expects the growing use of eDNA methods and DNA examination will assist her team make sense of the invader, financial support for the project has been hard to obtain.

"Everyone wants to give funding for protecting frogs," says the researcher. "But it's more difficult to find financial backing for an invasive frog that you might want to control."