Deep 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 coastlines.
A new study led by researchers across the University of California system in the United States and researchers in Mexico focuses on this luxuriant red mangrove forest. This “lost world” is located far from the coast along the banks of the San Pedro Martir River, which runs from the El Petén rainforests in Guatemala to the Balancán region in Tabasco, Mexico.
Because the red mangrove (Rhizophora mangle) and other species present in this unique ecosystem are only known to grow in salt water or somewhat salty water, the binational team set out to discover how the coastal mangroves were established so deep inland in fresh water completely isolated from the ocean. Their findings were published Oct. 4 in the Proceedings of the National Academy of Sciences of the United States of America.
Integrating genetic, geologic, and vegetation data with sea-level modeling, the study provides a first glimpse of an ancient coastal ecosystem. The researchers found that the San Pedro mangrove forests reached their current location during the last interglacial period, some 125,000 years ago, and have persisted there in isolation as the oceans receded during the last glaciation.
The study provides a snapshot of the global environment during the last interglacial period, when the earth became very warm and polar ice caps melted entirely, making global sea levels much higher than they are 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 more than 100,000 years,” said study co-author Octavio Aburto-Oropeza, a marine ecologist at Scripps Institution of Oceanography at UC San Diego and a Pew Marine Fellow. “There is certainly more to discover about how the many species in this ecosystem adapted throughout 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.”
Combining multiple lines of evidence, the study demonstrates that the rare and unique mangrove ecosystem of the San Pedro River is a relict—that is, organisms that have survived from an earlier period—from a past warmer world when relative sea levels were six to nine meters (20 to 30 feet) higher than at present, high enough to flood the Tabasco lowlands of Mexico and reach what today are tropical rainforests on the banks of the San Pedro River.
About Scripps Oceanography
Scripps Institution of Oceanography at the University of California San Diego is one of the world’s most important centers for global earth science research and education. In its second century of discovery, Scripps scientists work to understand and protect the planet, and investigate our oceans, Earth, and atmosphere to find solutions to our greatest environmental challenges. Scripps offers unparalleled education and training for the next generation of scientific and environmental leaders through its undergraduate, master’s and doctoral programs. The institution also operates a fleet of four oceanographic research vessels, and is home to Birch Aquarium at Scripps, the public exploration center that welcomes 500,000 visitors each year.
About UC San Diego
At the University of California San Diego, we embrace a culture of exploration and experimentation. Established in 1960, UC San Diego has been shaped by exceptional scholars who aren’t afraid to look deeper, challenge expectations and redefine conventional wisdom. As one of the top 15 research universities in the world, we are driving innovation and change to advance society, propel economic growth and make our world a better place. Learn more at ucsd.edu.