Researchers Discover 'Cryptic' Methane-Fueled Ecosystem in Mexico’s Yucatan Peninsula

A new study has led to the fantastical discovery of a methane based-ecosystem under water. 

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The cave-diving researchers went down the Ox Bel Ha cave network of the northeastern Yucatan, to unearth what the USGS, called a "cryptic" process. 

The Ox Bel Ha cave network is described as a subterranean estuary since the flooded cave passages consist of distinct water layers like freshwater by rainfall and salt water from the coastal ocean, the United States Geological Survey, USGS, which called the process "cryptic" noted. 

This subterranean estuary complex covers the region nearly the size of Galveston Bay, which is the seventh largest surface estuary in the United States.

“The processes we are investigating in these stratified groundwater systems are analogous to what is happening in the global ocean, especially in oxygen minimum zones where deoxygenation is a growing concern,"  John Pohlman, study's coauthor and a USGS biogeochemist whose work from the early 90s motivated the research, told the United States Geological Survey, USGS. 

"Although accessing these systems requires specialized training and strict adherence to cave diving safety protocols, relative to the complexity of an oceanographic expedition, the field programs we organize are simple and economical."

Scientists from Texas A&M University at Galveston, TAMUG, the U.S. Geological Survey, along with a team of collaborators from Mexico, The Netherlands, Switzerland along with other U.S. institutions, were involved in the research known to be one of the most detailed ecological studies ever conducted for a coastal cave ecosystem. 

"The opportunity to work with an international team of experts has been a remarkable experience for me," David Brankovits, the paper’s lead author, said, according to USGS. 

"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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The study revealed an interesting phenomenon of how the microbes deep within the caves were surviving on dissolved organic material like methane that percolated through the ceiling of the caves. 

"The freshwater portion of the caves and the sinkholes, which are used to access the caves and are referred to locally as cenotes, are important sources of freshwater for communities throughout the Yucatan," USGS's website elucidated.

Adding, "Methane in the caves forms naturally beneath the jungle floor." 

The microbes and the bacteria which form the basis of the cave ecosystem then feed on the methane produced, further fueling a food web that is dominated by crustaceans, like a cave-adapted shrimp species that obtains about 21 percent of its nutrition from methane. 

"Providing a model for the basic function of this globally-distributed ecosystem is an important contribution to coastal groundwater ecology and establishes a baseline for evaluating how sea level rise, seaside touristic development, and other stressors will impact the viability of these lightless, food-poor systems,"  Tom Iliffe, a marine biology professor at TAMUG told the USGS.