You are going to be sailing in areas where there are Posidonia seagrass meadows. We urge you to be extremely vigilant. These meadows form crucial underwater ecosystems in the Mediterranean, but they are fragile and threatened by a number of human activities, in particular anchoring of recreational craft.

An underwater plant of the Mediterranean

Posidonia (Posidonia oceanica) is a unique marine plant that’s endemic to the Mediterranean Sea. It is not a seaweed but a true flowering plant, with roots, stems, leaves and flowers. You’ll recognise it by its long, green, ribbon-shaped leaves. Posidonia grows in meadows, forming vast underwater prairies. It reproduces mainly by rhizomes and sometimes by seeds.
Posidonia meadows are found in the shallow coastal waters of the Mediterranean, from a depth of 1 to around 40 metres, in clear, well-lit waters. These meadows are particularly abundant in sheltered bays where conditions of temperature, salinity and light are ideal for their growth.
Practically the whole of the Mediterranean coastline is involved here: the shores of France, Italy, Croatia, Greece, Spain, Turkey, Tunisia, and more. 

An essential ecological role

Posidonia seagrass meadows provide a habitat and a source of food for a multitude of marine species, including fish, molluscs and crustaceans. They are also ideal spawning grounds and nurseries for young fish.
Like real underwater forests, seagrass beds act as carbon sinks, helping to combat climate change: they can store up to 300 tonnes of carbon per hectare. That’s 3 to 5 times more than tropical forests, and this, over hundreds of thousands of hectares. And not to mention their contribution to the production of oxygen, the protection of coasts by attenuating the impact of waves, the preservation of beaches where it accumulates in banks, etc. The loss of these meadows would have serious ecological and economic consequences for the Mediterranean.

A protected species under threat

Despite their importance, Posidonia meadows are extremely fragile and are threatened by a number of human activities. Boat anchoring, pollution, coastal urbanisation, trawling and climate change are all factors that contribute to their degradation. Seagrass beds are particularly sensitive to anchoring by boats: anchors can uproot these plants and create almost irreparable ‘scars’ in Posidonia meadows, as Posidonia rhizomes grow very slowly (a rate of just 1 cm per year).The presence of these meadows dates back between 60 and 100 million years, when terrestrial flowering plants, which resembled the rushes plant family of today, returned to the marine environment where their distant ancestors came from. Don’t be the one to destroy this extraordinary heritage in a matter of minutes.

Please note: Posidonia has been a protected species throughout the Mediterranean since 1995 and is classed as a habitat of European interest. Ensure you are aware of the regulations in force!

As a boater, you have a key role to play in protecting Posidonia meadows. Here are a few measures you can take to minimise your impact:

• 1. Before setting off, consult the maps that indicate the presence of Posidonia meadows. There are several free apps that can help you, such as Nav&Co or Donia. Download them.
• 2. Don’t anchor in Posidonia meadows: opt for sandy bottoms or consider picking up a mooring buoy whenever possible.
• 3. Respect protected areas: some regions have marine protected areas where anchoring and other activities are regulated to protect the seagrass meadows.
• 4. In all cases, adapt your anchoring technique: to avoid scraping the seabed, you must take care to bring your anchor back up in line with the boat, even if you are on sand.
• 5. Avoid generating any pollution at sea.
• 6. Share with others: not all boaters are aware of the importance of Posidonia seagrass meadows. And set an example!

By adopting these practices, you’ll be helping to preserve Posidonia seagrass meadows and the health of Mediterranean marine ecosystems. Protecting these underwater treasures is an essential and shared responsibility for future generations.

This blog article was created in collaboration with Alliance Posidonia.
For more information, visit their website: https://www.alliance-posidonia.fr/