If you enter the heart of the Yucatan peninsula, you may come across a relic of the ancient past of the Earth.
Mangroves usually exist on the coasts : they are forests that flourish on the banks of the mouths of rivers but, in this case, deep in the Yucatan peninsula, a team of researchers has discovered a mangrove forest in the river San Pedro Mártir , more than 200 kilometers from the ocean, between the El Petén rainforest in Guatemala and the Balancán region in Tabasco, Mexico.
The experts, who present their discovery in the journal Proceedings of the National Academy of Sciences, have revealed a wonderful river ecosystem of red mangroves that is, in essence, a time capsule. It has been “trapped in time for more than 100,000 years,” explains Octavio Aburto-Oropeza, a marine ecologist at the Scripps Institution of Oceanography at UC San Diego and a co-author of the work.
It looks like nothing known
This mangrove forest is genetically distinct from other populations of red mangroves. It has existed in isolation, resisting the changes in the environment that have occurred on our planet over the decades.
Living organisms in this environment can shed light on our past, revealing how nature adapted to ancient climate change and survived.
“We hope that our results will convince the government of Tabasco and the Mexican environmental administration of the need to protect this ecosystem,” the authors write. “The history of the Pleistocene glacial cycles is written in the DNA of your plants waiting for scientists to decipher it but, more importantly, the San Pedro mangroves warn us about the dramatic impact that climate change could have in the coastal plains of the Gulf of Mexico if we do not take urgent action to stop the emission of greenhouse gases ”.
A vision of the past
Along the banks of the San Pedro Mártir river grows a lush ecosystem of red mangroves. Because the red mangrove ( Rhizophora mangle ) and other species present in this unique ecosystem are necessarily dispersed by ocean water, their presence inland in the El Petén rainforests is puzzling and difficult to explain , scientists say.
By integrating genetic, geological, and vegetation data with sea-level models, they found that the San Pedro mangrove forests reached their current location during the last interglacial period, about 125,000 years ago, and have persisted at this location in isolation through as the oceans receded during the last ice age . According to their study, this lost mangrove forest was between 6 and 9 meters higher than it is today, high enough to flood the lowlands of Tabasco and reach what are currently the rainforests on the banks of the San Pedro River.
“We certainly need to find out more about how many species in this ecosystem have adapted to different environmental conditions over the last 100,000 years. The study of these past adaptations will change. It is very important to better understand future climate conditions , “say the researchers.
The authors note that the region surrounding the study sites was systematically deforested in the 1970s by a wrong development plan; the banks of the San Pedro river were only saved because the machines could not reach the area. The area is still threatened by human activities, so they have emphasized the need to protect this biologically important area.
Reference: Octavio Aburto-Oropeza, Carlos Manuel Burelo-Ramos, Exequiel Ezcurra, Paula Ezcurra, Claudia L. Henriquez, Sula E. Vanderplank, and Felipe Zapata. Relict inland mangrove ecosystem reveals Last Interglacial sea levels. PNAS, 2021 DOI: 10.1073 / pnas.2024518118
