More than a billion years ago, a green glow appeared in ancient waters. It was discreet, almost invisible. Inside a cell lay a fragment of sunshine: a cyanobacterium, captured and domesticated, that became a tiny light-powered factory. This was how the first algae arose, long before dinosaurs, trees or even jellyfish. This partnership between two worlds, bacterial and eukaryotic, gave rise to one of the oldest kingdoms on our blue planet.

Submerged flowering plants have stems, leaves and rhizomes: underground stems that gradually spread horizontally. Seagrass meadows play a vital role in aquatic ecosystems, generating substantial quantities of oxygen, up to 14 litres a day per square metre. Beyond their remarkable contribution to oxygen production, these underwater meadows provide essential habitat, sheltering between 20% and 25% of the animal and plant species found in the Mediterranean. Their presence is therefore crucial to biodiversity and healthy marine ecosystems.