When a new island Appearing in the South Pacific in 2015, it presented an unprecedented opportunity not only for geologists and volcanologists, but also for biologists and ecologists.
The appearance of a new island offers the opportunity to learn how ecosystems begin, beginning with microbial pioneers, which in this way colonize new land before plants or animals appear.
The island of Hunga Tonga-Hunga Ha’apai (Hunga Tonga) didn’t last long – after being formed by a volcanic eruption in 2015 destroyed by another eruption in early 2022.
However, in the seven years of its existence, the island has revealed some interesting secrets.
In a new study, researchers report evidence of an unexpected community of microbes on the island that metabolize sulfur and atmospheric gases, similar to organisms that inhabit very different habitats: hot springs or deep-sea hydrothermal vents.
“We didn’t see what we expected” says microbial ecologist Nick Dragone of the University of Colorado.
“We thought we would see organisms found when a glacier retreats, or cyanobacteria, more typical early colonizer species – but instead we found a unique group of bacteria that metabolize sulfur and atmospheric gases.”
Dragone and other researchers collected 32 soil samples from the island on surfaces ranging from sea level to the crater’s top and about 120 meters high. They then extracted and sequenced DNA from the samples.
Plants populated the island fairly quickly after it formed, likely thanks to seeds found in bird droppings, but researchers focused their collection efforts on bare surfaces.
They found bacteria and archaea in all of their samples from the volcano’s cone, although these microbes were less diverse than microbes from nearby vegetation areas — and very different.
It would make sense for the first microbes on a new island to come from either seawater or bird droppings, but that doesn’t seem to be the origin of these strange bacteria and archaea. Rather, the researchers suspect that these microbes could come from deep underground.
“One of the reasons we think we’re seeing these unique microbes is because of properties associated with volcanic eruptions: lots of sulfur and hydrogen sulfide gas, which likely power the unique taxa we’ve found,” Dragone said says.
“The microbes were most similar to those found in hydrothermal vents, hot springs like Yellowstone and other volcanic systems. Our best guess is that the microbes came from these types of sources.”
The opportunity to study such a system is rare. Big eruptions are one thing; Seeing an undescribed ecosystem evolve on a newly formed volcanic island is another.
In the past 150 years, Hunga Tonga is only the third such landmass to appear and persist for more than a year, the researchers say, and the first in the tropics.
While scientists also flocked to study the arrival of life on previously newly formed islands, they focused more on plants and animals than microbes.
“These types of volcanic eruptions happen all over the world, but they don’t usually produce islands,” Dragone said says. “We had an incredibly unique opportunity. Never before had anyone comprehensively studied the microorganisms on such an island system at such an early stage.”
And no one will again have the opportunity to study the inhabitants of the island, at least not directly. Seven years after emerging from the Pacific, Hunga Tonga disappeared spectacularly.
When the volcano erupted again in January 2022, it produced the largest explosive eruption of the 21st century, with the highest vapor and ash cloud in recorded history. Hunga Tonga was wiped out – but not before scientists were able to learn intriguing details about its short life.
“We’re obviously disappointed that the island disappeared, but now we have a lot of predictions about what happens when islands form,” Dragone said says.
“So if something forms again, we would like to go there and collect more data. We would have a game plan on how to investigate it.”
The study was published in mBio.
