Hidden mangrove forest in Yucatan Peninsula reveals ancient sea levels
In the heart of the Yucatan Peninsula, an ancient mangrove ecosystem flourishes more than 200 kilometers (124 miles) from the nearest ocean. This is unusual because mangroves – salt tolerant trees, shrubs, and palms – are typically found along tropical and subtropical coasts.
A new study led by system researchers from the University of California in the United States and researchers from Mexico focuses on this lush red mangrove forest. This “lost world” is located far from the coast along the banks of the San Pedro Martir River, which stretches from the rainforests of El Petén in Guatemala to the Balancán region in Tabasco, Mexico.
Because the red mangrove (mutilate Rhizophora) and other species present in this unique ecosystem only grow in salty or slightly salty water, the binational team set out to discover how coastal mangroves became established so deep inland in fresh waters completely isolated from the ocean. Their findings were published in the Proceedings of the National Academy of Sciences of the United States of America.
By integrating genetic, geological and plant data with sea level modeling, the study provides a first glimpse of an ancient coastal ecosystem. Researchers found that the mangrove forests of San Pedro reached their current location during the last interglacial period, around 125,000 years ago, and persisted there in isolation as the oceans retreated during the last ice age.
The study provides a snapshot of the global environment during the last interglacial period, when the Earth got very hot and the polar ice caps completely melted, causing global sea level to rise much higher than today.
“The most amazing part of this study is that we were able to examine a mangrove ecosystem that has been trapped in time for over 100,000 years,” said study co-author Octavio Aburto-Oropeza, an environmentalist. sailor at the Scripps Institution of Oceanography at UC San. Diego and a PEW Marine member. “There is certainly more to discover about how the many species in this ecosystem have adapted to different environmental conditions over the past 100,000 years. Studying these past adaptations will be very important for us to better understand future conditions in a changing climate.
By combining multiple data sources, the study demonstrates that the rare and unique mangrove ecosystem of the San Pedro River is a relic, i.e. organisms that survived an earlier period, of a world warmer where the relative sea level was six to nine. meters (20 to 30 feet) higher than today, high enough to inundate the Tabasco Lowlands in Mexico and reach what are now tropical rainforests on the banks of the San Pedro River.
The study highlights the vast landscape impacts of past climate change on the world’s coasts and shows that during the last interglacial period much of the lowland coastal areas of the Gulf of Mexico were underwater. In addition to providing important insight into the past and revealing the changes undergone by the Mexican tropics during the Ice Ages, these results also open up opportunities to better understand future scenarios of relative sea level rise as the change. climate is advancing in a man-dominated world.
Carlos Burelo, botanist at the Universidad Juárez Autónoma de Tabasco and native of the region, drew the attention of the rest of the team to the existence of this relict ecosystem in 2016. “I used to fish here. and playing in those mangroves as a child, but we never knew exactly how they got there, ”said Burelo. “It was the driving question that brought the team together. “
Burelo’s fieldwork and surveys of biodiversity in the region laid the solid foundation for the study. His remarkable discovery of the ancient ecosystem is documented in “Memories of the Future: the modern discovery of a relic ecosystem”, a Award-winning short film produced by former Scripps student Ben Fiscella Meissner (MAS MBC ’17).
Felipe Zapata and Claudia Henriquez from the University of California at Los Angeles (UCLA) led the genetic work to estimate the origin and age of the relict forest. By sequencing segments of the red mangrove genome, they were able to establish that this ecosystem migrated from the coasts of the Gulf of Mexico to the San Pedro River over 100,000 years ago and remained isolated there after the ocean receded. when temperatures dropped. While mangroves are the most notable species in the forest, they have found nearly 100 other smaller species that also have ocean lineage.
“This discovery is extraordinary,” said Zapata. “Not only are the red mangroves here with their origins imprinted in their DNA, but the entire coastal lagoon ecosystem of the last interglacial found refuge here.”
Paula Ezcurra, scientific program manager at the Climate Science Alliance, carried out the sea level modeling, noting that the coastal plains of the southern Gulf of Mexico are so low that a relatively small change in sea level can produce dramatic effects inland. She said that a fascinating part of this study is how it highlights the benefits of working collaboratively between scientists from different disciplines.
“Not every piece of history alone is enough, but when taken together, genetics, geology, botany and field observations tell an incredible story. Each researcher involved brought their expertise to help us uncover the mystery of a forest over 100,000 years old, ”said Ezcurra, a former student of Scripps Oceanography (MAS CSP ’17).
Fieldwork was led by the team’s ecologists: Octavio Aburto-Oropeza, Paula Ezcurra, Exequiel Ezcurra from UC Riverside and Sula Vanderplank from Pronatura Noroeste. By visiting the study sites several times starting in 2016, they collected rocks, sediments and fossils for laboratory analysis, which helped them identify evidence from the past compatible with a marine environment.
The authors note that the region surrounding the study sites was systematically deforested in the 1970s by an ill-advised development plan; the banks of the San Pedro River were only spared because bulldozers could not reach it. The area is still threatened by human activities, so the researchers stressed the need to protect this biologically important area in the future.
“We hope that our results will convince the government of Tabasco and the environmental administration of Mexico of the need to protect this ecosystem,” they said. “The story of the Pleistocene ice cycles is written in the DNA of its plants while it waits for scientists to decipher it but, more importantly, the mangroves of San Pedro warn us of the dramatic impact that climate change could have. have on the coastal plains of the Gulf of Mexico if we don’t take urgent action to stop greenhouse gas emissions. “
– This press release was originally posted on the University of California – San Diego website