Posidonia seagrass

Photo: Chalon Boesel · CC BY-NC

Posidonia oceanica is the Mediterranean's keystone benthic ecosystem engineer, producing oxygen, sequestering carbon at rates comparable to tropical mangroves, and providing nursery habitat for over 400 fish species including most commercially important Mediterranean fish. The Steno meadow extends across sandy flats between 8 and 18 m depth, its mats of dead compressed leaf material ('matte') representing centuries of growth — Posidonia grows at just 1 to 7 cm per year, making established meadows potentially thousands of years old. Anchoring damage to Posidonia meadows is an acute conservation issue in Crete, and Steno's healthy meadow edge reflects the site's restricted access.