marți, 7 februarie 2012

Patch of seagrass is world's oldest living organism - 80.000 years old !

It's green and very, very old. A swathe of seagrass in the Mediterranean could be the oldest known living thing on Earth.

Carlos Duarte of the University of Western Australia in Perth sequenced the DNA of Posidonia Oceanica at 40 sites spanning 3500 kilometres of seafloor, from Spain to Cyprus. One patch off the island of Formentera was identical over 15 kilometres of coastline.

Like all seagrasses, Posidonia oceanica reproduces by cloning, so meadows spanning many kilometres are genetically identical and considered one organism.

Given the plant's annual growth rate the team calculated that the Formentera meadow must be between 80,000 and 200,000 years old, making it the oldest living organism on Earth. It trumps a Tasmanian seagrass, Lomatia tasmanica, believed to be 43,600 years old.

The endemic Mediterranean seagrass Posidonia oceanica ranks amongst the slowest-growing and longest-lived plants in existence . This structural species lacks native competitors and major predators in the littoral marine habitat (0–40 m) it occupies, leading to the development of extensive, monospecific meadows .However, these are presently declining throughout its range. Previous studies provided evidence that Posidonia oceanica meadows have grown continuously at particular locations for over 6000 years and that clone mates occur at distances up to at least 80 metres that can only be covered over a minimum of 600 to 700 years of clonal growth. Altogether these results suggest that P. oceanica clones can achieve millenary life spans.

Despite its historical robustness, Duarte says the patch of P. oceanica is now threatened by climate change. The Mediterranean is warming three times faster than the world average, and each year P. oceanica meadows decline by around 5 per cent. "They have never experienced the speed of climate that the Mediterranean is currently experiencing," he says.

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