The ancient organism in the bay
Off the coast of Porquerolles, one of the Îles d'Hyères, lies an immense, ancient organism. It is a vast underwater meadow of Neptune Grass (Posidonia oceanica), a species of seagrass endemic to the Mediterranean. Genetic studies have revealed that some of these meadows are clonal colonies, meaning thousands of distinct-looking plants spread over many kilometers are actually a single individual connected by underground rhizomes. The largest known clone of P. oceanica, located between the Spanish islands of Ibiza and Formentera, stretches 8 kilometers across and is estimated to be around 100,000 years old, making it one of the oldest living things on Earth. The meadows within the Port-Cros National Park, which includes Porquerolles, are part of this same remarkable biological phenomenon.
This organism's extreme age is a result of its slow growth and method of reproduction. Posidonia oceanica spreads primarily through asexual reproduction, sending out horizontal underground stems called rhizomes. The growth is incredibly slow, with horizontal rhizomes extending just 1 to 6 centimeters per year. This gradual expansion, over millennia, allows a single plant to colonize huge areas of the seabed. The plant forms a dense mat of rhizomes and roots that can be several meters thick, trapping sediment and building up the seafloor over centuries. The individual leaves have a lifespan of about a year, but the organism as a whole persists, steadily growing outward.