2021. Warning. Endangered Posidonia, forest of the sea

Welcome to the special section “GdV 5th Years.” We are introducing you, day by day, An article from the archives of the Journal of Sailing, starting in 1975. A word of advice, get in the habit of starting your day with the most exciting sailing stories-it will be like being on a boat even if you are ashore.

Posidonia, the fragile forest of the Mediterranean Sea

Taken from the 2021 Sailing Journal, Year 47, No. 04, May, pp. 82/87.

Posidonia the lung that supplies the Mediterranean with oxygen is disappearing. To save the fragile forest of our seas we all need to mobilize. Because there are steps and actions we can take and urge to save the seas. And ourselves.

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Those sailing along the Italian coasts may happen to come across one of those bright green prairies that stand out from the seabed across the blue sea. At first glance they look like algae, but they are actually aquatic plants and constitute not only a valuable habitat for marine species, but exactly like tropical forests on land through photosynthesis they enrich the sea with oxygen, so much so that they are considered the “green lung” of the Mediterranean. We are talking about Posidonia Oceanica, a marine plant that in spite of its scientific name lives only in the Mediterranean and grows in a few centimeters of water up to more than 40 meters deep because like any plant, even underwater. Under the right conditions, Posidonia forms roots, stems, leaves and flowers and colonizes sandy or gravelly bottoms, forming vast, very dense prairies that exceed 700 plants per square meter. These green forests represent the most productive natural environments in the Mediterranean. In fact, within them they provide food and shelter for about 400 plant species and 1,000 animal species.

A valuable plant that produces oxygen and protects the seabed

Posidonia meadows then play an important role as a barrier against seabed erosion. In fact, with their leaves they brake wave motion and currents, while the dense network of roots holds back sand and other sediment. Even when it dies, Posidonia continues to serve the environment: its leaves carried by currents along our coasts form shoals that protect shorelines and sand dunes from storm surges. But Posidonia ‘s most important function is that it produces oxygen: it is estimated that each square meter of healthy seagrass can release up to 14-16 liters of oxygen per day. It acts in other words as a true biological system that regulates the uptake of CO2 into the sea and the atmosphere. From all this it is clear how Posidonia Oceanica has an extraordinary value for the Mediterranean. A value, however, that is destined to decline if we do not take action soon.

Threatened by pollution, artificial beaches and trawling

Posidonia currently occupies 3 percent of the Mediterranean Sea, which corresponds to an area of 38,000 km2. Unfortunately, however, its meadows are disappearing at a rapid rate: researchers estimate that 34 percent of Posidonia has already disappeared in the Mare Nostrum in the past 50 years, and its rate of regression is 5 percent per year. In practice, every 30 minutes we lose an area covered with Posidonia equivalent to a soccer field. An alarm raised as early as 1990 when Posidonia was put on the red list of protected species because it is endangered. Threatening the “green lung” of our sea are widespread pollution, the presence of microplastics, but also trawling and the construction of coastal works, artificial beaches and breakwaters that change the rate of sedimentation in the sea. Added to all this is climate change, which causes strong changes in sea currents and altered conditions of temperature, salinity and composition of the sea in which Posidonia lives. The trouble is that this aquatic plant grows very slowly, just 2 cm per year, so such losses are irreversible, as Posidonia recovery takes several centuries.

Less seagrass means a poorer Mediterranean.

Losing Posidonia means having a Mediterranean Sea poorer in oxygen, health and biodiversity. Which also translates into economic damage affecting the entire Mare Nostrum community: less catch for the fishing industries, a more suffering blue economy, nautical and beach tourism penalized. Not to mention the enormous costs of reforesting the seabed. Do you know how much it costs to reconstitute one square meter of seagrass? About 800 to 1,000 euros. For all these reasons, Posidonia meadows are considered an ecosystem to be safeguarded by the European Community and subject to specific protection laws that have also been ratified in Italy, such as the EEC Directive No. 43/92 relating to the “conservation of natural and semi-natural habitats and of wild flora and fauna,” as well as the 1979 Bern Convention relating to the “Conservation of European Wildlife Habitats” and the 1995 Barcelona Convention for the Protection of the Mediterranean Sea from Pollution.

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Here’s how we boaters can save it

However, the protection of Posidonia cannot only come through restrictive laws, but enter into our environmental consciousness. We yachtsmen can also contribute, for example by avoiding, when we stop at anchor, dropping anchor on a Posidonia meadow. In fact, the anchor and the chain of our sailboats with their continuous movements caused by wind, currents and wave motion have a strong impact on the prairie, because they tear up its roots, stems and leaves: consider that every time you pull the anchor away from a Posidonia prairie on average you can destroy up to 34 bundles of plants, or about one square meter. In short, to anchor at anchor in an environmentally friendly and nature-friendly way, all that remains is to take advantage of sandy or rocky bottoms.

Environmentally friendly anchors and green behavior

Once we have dropped anchor on a safe, Posidonia-free seabed, we boaters can then implement other behaviors that are respectful of this fragile aquatic plant. For example, it is important not to discharge black water and gray water into the sea: each cabin cruiser should embark two dedicated tanks for responsible discharge in port. Another basic rule of the “eco” yachtsman is not to litter the sea, especially plastic, as well as detergents, sunscreen, oils, hydrocarbons and other toxic liquids that would contaminate the surrounding sea and Posidonia meadows. Finally, it would be good not to disturb the inhabitants of the green prairies with disturbing noises or bumping into leaves when swimming or diving.

Download the Donia App to avoid the grasslands.

Precisely in an effort to limit the phenomenon of destructive anchoring of Posidonia by sea-goers, the company Andromède Océanologie recently launched Donia(www.donia.fr), a free app that allows boaters and fishermen to locate anchorage sites free of seagrass so as not to damage them with anchors and chains. Available on smartphones and tablets, the app’s cartography indicates the nature of the seabed, depth, regulations at sea, satellite images, but also ports and especially anchorage areas. The accuracy of the data thus allows users to anchor away from underwater grasslands, while respecting the law and safeguarding marine ecosystems.

Posidonia transplantation: is it possible?

In recent years in Italy, the idea of protecting Posidonia has been developed through transplanting interventions that can accelerate the slow colonization of these plants and encourage the restoration of the degraded ecosystem by compensating for the damage caused by the construction of ports or coastal infrastructure or the laying of submarine cables. Reforestation of our seabed has already been experimented in Civitavecchia where 10,000 square meters of Posidonia were transplanted, but the same has also been done in Puglia, Calabria, Sicily Sardinia, Tuscany and Lazio. It is not easy to carry out the transplantation successfully because there are so many critical factors: the donor and recipient bottoms must have very similar characteristics of water temperature and salinity, then wave motion, currents, the presence of algae, etc. influence the transplantation. There is currently an EU-funded project, Life Seposso(www.lifeseposso.eu) that is evaluating the most effective techniques for reforestation and raising awareness of the importance of Posidonia. He who destroys, must rebuild, that is the axiom. After all, someone said that a civilized country is also distinguished by the way it treats its plants, including marine plants like Posidonia, which make the Mediterranean breathe and with it all of us.

by David Ingiosi

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