Mexico’s Yucatan Peninsula is inarguably most famous for one thing: It was ground zero for the asteroid-capped dinosaurian apocalypse 66 million years ago. The entire region, however, is full of unexplored caves and cenotes (sinkholes), and a new study has revealed that some of them are teeming with unconventional life too.
The adventurous team that made the discovery – led by Texas A&M University at Galveston and the United States Geological Survey (USGS) – were conducting a comprehensive ecological study of the Ox Bel Ha cave network, which is found running up along the northeastern coast of the peninsula.
They found that within it there are bacterial colonies that live in low-oxygen waters and in near-pitch darkness. There isn’t even much organic matter falling from above to feed on. Instead, they live by consuming invisible, dissolved matter primarily comprised of carbon and methane.
They’re not alone. The team explain that these bacteria are the “lynchpin” for the entire submarine ecosystem, and that their odd way of getting nutrition has been adopted by some of the crustaceans that they live alongside.
Writing in Nature Communications, the international team of scientists explain that, for example, around 21 percent of the diet of one shrimp species is solely methane.
Unlike the deep ocean, where methane ekes upwards from hydrothermal vent systems and seafloor bacteria, this labyrinth’s methane forms beneath the jungle floor up at the surface. It eventually seeps downwards into these flooded caves, which ultimately forms the basis for this bizarre ecosystem.
As food webs go, this is as far from conventional as you’re likely to get.
Methane may seem odd to us oxygen-breathing land-walkers, but it’s actually a vital component used by life that lives in the world’s oft-unexplored extreme environments.
It’s well known that plenty of areas deep within the oceans and concealed beneath Arctic permafrost and vast Antarctic ice sheets contain methanogens, microbial organisms belonging to the archaea domain of life that produce methane. The methane-consuming ecosystem within the Ox Bel Ha caves adds a delightful new wrinkle to the story.
Although this is an indubitably very cool discovery for evolutionary ecologists, it does highlight a worrying pattern that’s being seen across the world’s oceans at present. Thanks to increased amounts of carbon dioxide and methane in the world’s oceans – something largely driven by climate change – oxygen levels are dropping off.
“Deoxygenation is a growing concern,” co-author John Pohlman, a USGS biogeochemist, said in a statement. “The processes we are investigating in these [cave] systems are analogous to what is happening in the global ocean.”
In short, methane’s great for extremophiles, but the more of it that seeps into the oceans, the less likely a plethora of other lifeforms will survive in the long term.