Posidonia Oceanica, also known as Neptune Grass, is an endemic seagrass from the Mediterranean. It is commonly mistaken with algae but in fact it is a plant and it is particularly important for the ecosystems as it produces 5 times the amount of oxygen as a byproduct compared to the Amazon rainforest.

Posidonia meadows are also key markers for clean water and lack of pollution and act as a shelter for around 1.000 different species including endangered Noble Pen Shells (Pinna Nobilis), Nudibranchs and Pipefish.

Another important function is helping keep coastal erosion under control. The roots and rhizomes fixed on sandy bottoms prevent the loss of sediment due to currents and waves.

Interestingly, the same thing happens when the leaves die and wash up onshore, creating big organic deposits that act as buffers when swells hit the beaches, preventing sand loss.

Posidonia meadows represent only 3% of the total Mediterranean underwater surface and one of the largest known meadows is located south of Ibiza island stretching as far as Formentera, ranging approximately 8km and being 100.000 old.

In 1999 it was declared Human Heritage

Research shows in between 13% and 38% of the total posidonia coverage has been lost over the past 60 years and current meadows have lost over a 50% density (Source: Biological Conservation)

Water pollution from untreated sewage and runoffs and recreational sailing negligent anchoring and major threats for the meadows and several organisations such as Manu San felix’s Associació Vell Marí are fighting to protect the Posidonia and to raise awareness about the importance of it for a healthy ecosystem and a cristal clear water.

Photo and Text by Marc Dura