There is a surprising mangrove ecosystem in Tabasco, Mexico. Photo: Octavio Aburto / Mares Mexicanos
More than 100 miles from the Gulf of Mexico, an ecosystem of salt-tolerant trees is flourishing along a freshwater river. A team of researchers recently investigated how this green oasis has gone so far from its typical habitat, and found that the forest was deserted on land during the last interglacial period more than 100,000 years ago.
“We found these beautiful lagoons, a beautiful forest of red mangroves,” marine ecologist Octavio Aburto said during a phone call. “It’s like a lost world.”
Aburto, of the Scripps Institution of Oceanography in UC San Diego, is part of a team that recently conducted a genetic analysis of the forest along with a geological analysis to determine its age. They also examined the flora in the area (in addition to the red mangroves) and performed sea level modeling to determine where the ocean was during the Pleistocene epoch, which ended nearly 12,000 years ago. All that out-of-place ecosystem research was published today in the Proceedings of the National Academy of Sciences.
Lilypads in the mangrove forest, where many plants now typically live in marine environments. Photo: Octavio Aburto
The forest is located on the banks of the San Pedro Mártir River and was discovered by Carlos Burelo, a botanist at the Universidad Juárez Autónoma de Tabasco who co-authored the recent paper. “I used to fish here and play on these mangroves as a child, but we never got to know exactly how they got there,” Burelo said in a UC San Diego press release. “That was the question that brought the team together.”
Geological analysis by the team found fossils of marine gastropods, indicating that the area was not always a freshwater environment, an idea corroborated by sea level modeling. During the last interglacial period, the Earth was warm enough for the ice caps to melt completely. Sea levels were 20 to 30 feet higher than today, and the water now relegated to the Gulf of Mexico was much farther from land. The mangroves grew where it once was the edge of the ocean, but when the sea water receded, the forest remained. The ecosystem is what is called a wreck: a vestige of the ancient past that has managed to persist.
The team thinks the mangrove population has survived in the area thanks to the type of freshwater that has replaced the sea. The water is rich in calcium carbonate, thanks to the limestone rocks in the Tabasco region. Red mangroves can set up shop in calcium waters – without any sea water needed – although the situation is “very rare,” according to Aburto, who led the recent paper.
This mangrove forest hosts other organisms that typically live in saltwater ecosystems; the team recognized nearly 100 species that normally live near the oceans, including some cacti and orchids, and yet several miles were found off any coast.
Forests are under threat from humans, mainly due to agriculture. Photo: Octavio Aburto
Unfortunately, the ancient forest is under threat. Farming and hunting in the area have seen mangroves cut down and burned. By the 1970s, mangroves covered a wider stretch of the Tabasco region, but efforts to establish herds of cattle near the river relegated the last pieces of forest to the river banks.
“We hope this research will create support for further protection of this biodiversity reservoir,” Aburto said. “It can help us to understand not only the past conditions of this planet, but also to help us understand how we can better adapt to future changes.”
Although salt water is what allowed mangroves to set up shop in the first place, too much of a good thing can be a hassle. While these mangroves are far from land today, other mangrove forests are at imminent risk of drowning – being inundated by the very waters that call home.