Underwater caves have been described as one of Earth’s final unexplored frontiers. An international team recently delved into the flooded caves of the Yucatan Peninsula in Mexico and found methane and dissolved organic carbon sustain the food web in these caves, with an ecosystem similar to that of deep ocean cold seeps.

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Mayan lore described the underwater caves in Mexico as a fantastical underworld. While the caves aren’t mythical, they did hold surprises for the 10 scientists who recently conducted what the United States Geological Survey (USGS) described as “the most detailed ecological study ever for a coastal cave ecosystem that is always underwater.” These researchers found methane and the bacteria that eat it serve as the linchpin for the ecosystem. Study lead author David Brankovits of Texas A&M University at Galveston said in a statement, “Finding that methane and other forms of mostly invisible dissolved organic matter are the foundation of the food web in these caves explains why cave-adapted animals are able to thrive in the water column in a habitat without visible evidence of food.”

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They researched the Ox Bel Ha cave network, a subterranean estuary complex about the same size as Galveston Bay. Naturally-forming methane in these caves migrates downward, instead of upward as it normally would when formed in soils, so bacteria and microbes can feed on the methane.

Prior studies posited that vegetation and detritus comprised the majority of organic material for microbe food in the caves, according to USGS, so the scientists were surprised to discover just how important methane is to the caves’ food web. There’s little surface debris to serve as food deep in the caves, so microbes depend on methane as well as other dissolved organics that filter down from the caves’ ceiling. One cave-adapted shrimp species receives around 21 percent of its nutrition via methane.

The journal Nature Communications published the research online in late November. Scientists from institutions in the United States, Switzerland, the Netherlands, Norway, and Mexico contributed to the work.

Via the United States Geological Survey

Images via © HP Hartmann and the United States Geological Survey