When botanist Carlos Burelo was a young boy, he used to play among a grove of red mangroves along the banks of the San Pedro Martir River in the middle of Mexico’s Yucatan Peninsula. The funny thing is that mangroves typically grow in coastal salt waters, while these ones thrive in freshwater 124 miles inland.

“I used to fish here and play on these mangroves as a kid, but we never knew precisely how they got there,” said Burelo in a press release. Now, this question is the driving force behind research that may help us understand the impacts of past climate change on coastlines as well as predict the impacts of future sea level rise.

Thanks to Burelo’s initial curiosity, the research team decided to take a closer look at the mangroves and the unique ecosystem they support. The scientists studied the genetic history of the trees to figure out exactly when they were separated from their native saltwater coasts. They detailed their findings in an article published in the Proceedings of the National Academy of Sciences of the United States of America.

“[Mangroves’] genomes accumulate mutations every generation at a rate of about one in every 300 million letters of the genetic code, which will be passed on to future generations,” said Richard Nichols, an evolutionary geneticist at Queen Mary University of London who is not associated with the study in question. “By counting up the number of differences between two genomes it is possible to estimate the number of generations since those two genomes shared an ancestor.”

The researchers used this method to determine that the inland grove separated from coastal mangroves around 125,000 years ago, during the last interglacial period when the planet’s temperature was warmer, completely melting the polar ice caps and effectively raising sea levels by 20 to 30 feet.

This unique series of events makes the mangrove forest an ecosystem that has been preserved from a bygone era. According to Live Science, in addition to the mangroves themselves, the researchers discovered that nearly 100 other species native to the forest had ocean origins, such as turtles, fish, and vegetation.

Study co-author Felipe Zapata from UC Los Angeles was excited about this extraordinary discovery. “Not only are the red mangroves here with their origins printed in their DNA,” Zapata exclaimed, “but the whole coastal lagoon ecosystem of the last interglacial has found refuge here.”

These findings and continued work will help scientists predict how our current climate crisis may influence the region in the future, but this can only happen if the mangroves are maintained and preserved.

“We hope our results convince the government of Tabasco and Mexico’s environmental administration of the need to protect this ecosystem,” said the study authors. “The story of Pleistocene glacial cycles is written in the DNA of its plants waiting for scientists to decipher it but, more importantly, the San Pedro mangroves are warning us about the dramatic impact that climate change could have on the coastal plains of the Gulf of Mexico if we do not take urgent action to stop the emission of greenhouse gases.”

Source image: Gizmodo/Octavio Aburto