Marine vegetation
Mediterranean seagrass
Posidonia oceanica
Epipelagic zone
Some Posidonia meadows form a single clonal organism over 100,000 years old, potentially making it one of the oldest living things on the planet.
🗺️ Geographic range
Endemic to the Mediterranean Sea, where it forms vast meadows on sandy seabeds, from the shoreline down to 35 meters depending on water clarity.
📊 Population
Declining at an estimated 5% per year due to climate warming, coastal pollution, and boat anchoring, these meadows are strictly protected under the European Union's Habitats Directive.
Habitat
- Mediterranean Sea · Epipelagic zone · Permanent
🥚 Reproduction
Reproduces mainly asexually by cloning, allowing a single individual to spread over several kilometers and persist for tens of thousands of years; sexual reproduction through flowering exists but remains rare and poorly understood.
Behaviour
- Diet
- Autotrophic: it produces its own organic matter through photosynthesis, capturing light through its long ribbon-like leaves.
- Hunting
- None: it is a photosynthetic plant, not a predator.
- Communication
- None known.
- Social life
- Forms vast dense meadows ('underwater prairies') that host exceptional biodiversity and stabilize sandy seabeds.
Physiology
- Anatomy
- Unlike an alga, it is a true flowering plant with roots, stems, and ribbon-like leaves that can exceed a meter in length.
- Respiration
- Gas exchange through its leaves, releasing large amounts of oxygen into the surrounding water.
- Vision
- None: it has no sensory organs.
- Adaptations
- Its ability to clone itself indefinitely means it could theoretically persist without a time limit — one individual has been dated at over 100,000 years old.
🔗 Web of marine life
Predators
Partners
⚡ Its extraordinary abilities
- A single clonal individual may be over 100,000 years old, one of the oldest known living things
- Captures up to 15 times more CO2 per hectare than an equivalent area of Amazon rainforest
🏆 Records
Among the oldest living organisms ever recorded
A study dated one clonal Posidonia meadow at between 80,000 and 200,000 years old, potentially making it one of the oldest living things on Earth.
If you cross paths with this animal…
Risk: No danger to humans.
Behaviour: Motionless; dead-leaf 'banquettes' washed up on beaches play a protective role against coastal erosion.
Advice: Avoid anchoring a boat directly on a meadow, one of the main causes of its decline, and use designated mooring areas instead.
💡 Did you know?
- One Posidonia meadow discovered in the Mediterranean may be a single clonal organism between 80,000 and 200,000 years old.
- It captures up to 15 times more CO2 per hectare than an equivalent area of Amazon rainforest.
