Carlos Duarte of the University of Western Australia in Perth and his colleagues sequenced the DNA of the seagrass Posidonia oceanica at 40 sites across 2,100 miles of seafloor, from Spain to Cyprus, NewScientist.com reported Monday.
Posidonia oceanica reproduces by cloning, like all seagrass, so meadows spanning many miles are genetically identical and considered one organism, Duarte said.
One patch off the island of Formentera near Spain was identical over 9 miles of coastline, and given the plant's annual growth rate the researchers said they calculated the Formentera meadow must be between 80,000 and 200,000 years old, making it the oldest living organism on Earth.
Despite its longevity, Duarte says the patch of P. oceanica is now threatened by climate change as the Mediterranean is warming three times faster than the world average and P. oceanica meadows decline annually by around 5 percent.
"They have never experienced the speed of climate that the Mediterranean is currently experiencing," he said.