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Scientists have discovered the origin of a mysterious mangrove forest landlocked in the heart of Mexico’s Yucatán Peninsula.
Normally trees of this species – known as red mangroves, or mutilate Rhizophora – only grow in salt water, along tropical coasts. But this forest is located near the San Pedro River in the state of Tabasco, more than 200 kilometers from the nearest ocean. Somehow, these mangroves have adapted to live exclusively in this freshwater environment of southeastern Mexico.
The exact way in which this ecological conundrum came about has baffled scientists. But now, an international, multidisciplinary team of researchers has revealed that this displaced ecosystem began to develop around 125,000 years ago, when sea level was much higher and the ocean covered most of the land. region.
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“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,” lead author Octavio Aburto-Oropeza, marine ecologist at the Scripps Institution of Oceanography in the university. from California, San Diego, said in a press release. It was like reconstructing a “lost world”, he added.
How did it come to this?
Researchers have only recently started studying the San Pedro mangrove system, but local people have benefited from this unique ecosystem for generations.
“I used to fish here and play in these mangroves when I was a kid, but we never knew exactly how they got there,” co-author Carlos Burelo, botanist at the Autonomous University Juárez of Tabasco in Mexico who grew up near the forest, said in the statement. “It was the driving question that brought the team together.”
To find out how this coastal ecosystem got stranded so many kilometers from the coast in an alien environment, the researchers analyzed the DNA in the mangroves to see how different they were from other mangrove populations.
“Mangrove genomes accumulate mutations with each generation at a rate of about one in 300 million letters of the genetic code, which will be passed on to future generations,” Richard Nichols, an evolutionary geneticist at Queen Mary University in London who was not involved in the study, Live Science said. “By counting the number of differences between two genomes, it is possible to estimate the number of generations since these two genomes share an ancestor.”
This is one of the most accurate ways to date when two populations have isolated themselves. “If two populations have become isolated from each other, the most recent common ancestors of individuals from different populations must predate the period of isolation,” Nichols said.
Based on the number of genetic mutations accumulated in mangrove DNA, the team determined that mangroves have been isolated from the geographically closest coastal mangroves for around 125,000 years. Because global sea level was much higher 125,000 years ago due to warmer air temperatures, researchers suspect the region was once a coastline.
Therefore, the mangrove forest likely took root when the ocean was higher and managed to survive after retreating to modern levels, leaving the coastal ecosystem trapped inland and forcing it to retreat. adapt to the freshwater conditions provided by the San Pedro River.
Sea level change
Global sea levels have risen and fallen several times throughout Earth, due, in part, to the subtle changes in Earth’s orbit around the sun that cause the planet to receive more or less solar radiation, depending on the National Oceanic and Atmospheric Administration (NOAA).
During times when the Earth receives the least radiation, called ice maximums or ice ages, atmospheric temperature drops and ice caps cover much larger areas in the polar regions. When the planet receives the greatest amount of radiation, known as the interglacial period, the temperature rises and the ice caps melt, releasing more water into the oceans.
The last interglacial period ended about 120,000 years ago, according to NOAA, which agrees with researchers’ theory of mangrove forest and sea level rise.
However, previous models did not predict that the sea level at this time would be high enough to cover the mangrove forest, which currently sits 9 meters above sea level.
The region surrounding the forest is so low that a relatively small change in sea level can produce dramatic effects inland. the statement.
The researchers hope the findings could help predict how the region might be affected by climate change “Studying these past adaptations will be very important for us to better understand future conditions in a changing climate,” said Aburto-Oropeza.
Ancient relic
The researchers described the mangrove forest in the San Pedro River as a “relic,” an ecosystem that has survived an earlier period. And it’s not just the mangroves that have managed to survive – a hundred other species that thrived in or near the ancient ocean, including fish, turtles and plants, according to the statement.
“This discovery is extraordinary,” co-author Felipe Zapata, a geneticist at the University of California, Los Angeles, said in the statement. “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.”
Researchers aren’t sure exactly how the mangroves and the species that live there were able to adapt to freshwater conditions, but other researchers can now use the site to investigate these questions. “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,” said Aburto-Oropeza.
However, without protected status, the forest could be in danger. In the 1970s, a misguided development plan led to large parts of the region being affected by Deforestation, and the mangroves barely avoided destruction. But the forest is still very vulnerable to a similar situation 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,” the researchers wrote in their article. “The story of Pleistocene glacial cycles are written in the DNA of its plants, waiting for scientists to decipher them. “
The study was published on October 4 in the journal Proceedings of the National Academy of Sciences.
Originally posted on Live Science.
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