The seagrass Posidonia oceanica is a plant endemic to the Mediterranean, meaning it is found only in this sea. Its distribution is restricted to the infralittoral zone, extending from the surface down to a depth of 40 meters. As a marine plant, it is notable for its ability to form extensive meadows; these constitute one of the most productive communities in the coastal ecosystem, owing to their high primary productivity, the resident fauna they harbor, their role as a refuge for the larvae, juveniles, and adults of numerous fish species—including some of commercial importance—and their capacity to export organic matter through their decaying remains. In the islands, these meadows are popularly known as alguers or negre.