Posidonia oceanica

Posidonia oceanica , the posidonie of the Mediterranean , is a species of plants to flowers, of the family of the Posidoniaceae . It is not a Algue, although she lives under water. It is indeed about an underwater plant Angiosperme Monocotylédone. Like all the plants with flowers, they have root S, and reproduce thanks to the Fruit S which they produce.

On the 9 species of Posidonia , 8 are on the Australian coasts. Posidonia oceanica is for its part endemic of the the Mediterranean.

Description

This last growth on the funds between surface and 40 m of depth and the shape of vast herbaria. These herbaria constitute the major ecosystem of the Mediterranean. Drawing its name from the Greek god of the sea Poséidon, it plays several fundamental roles for the littoral seamen circle.

The herbaria which it form are places of spawning ground and nursery for many animal species. It also constitutes a source of food, sometimes important, for certain herbivorous species (sea urchin S, saupes, etc). Part of the production of sheets of an herbarium will be found exported, in the form of litter, worms of other distant ecosystems (beach, underwater canyon,…) where it will constitute an important source of carbon for the operation as of these ecosystems. It makes it possible to fix sea-beds thanks to the interlacing of its Rhizome S. Those pile up one year on the other, contributing to increase the level of the bottom gradually (approximately a Mètre by Siècle). It " piège" suspended particles and sediment, thus contributing to the maintenance of the clearness of water. The herbaria with Posidonia oceanica are regarded as essential formations in the storage of atmospheric carbon and the oxygenation of the medium.

In addition, the scientific discoveries of these last years make it possible to use Posidonia oceanica like indicator of the quality of the medium. Indeed, it informs, by its presence and its vitality, about the quality of the medium in which it develops. Its use is in particular recommended (as a magnoliophyte marine) to evaluate the ecological good state of the coastal water masses, within the framework of the Parent directive on Water of the European Community (N°2000/60/CE, of the European Parliament and the council - October 23rd, 2000).

The decline of the herbaria is mentioned on many Mediterranean coasts, and although it can have an origin naturalness, the human activities are often the cause. Indeed, this plant is threatened today by the urbanization and pollution of the shores (rejections of worn water and polluting substances, constructions on the Littoral, trawling and damping of the boats,…), and by the proliferation of the alga Caulerpa taxifolia .

Characteristics

Reef barrier

When the herbaria of posidonie develop with the bottom of splits very low depth, the plants level surface and can create a reef barrier, contributing to the formation of a particular Biotope.

Leashes of sea

The movements of the sea tend sometimes to lacerate the dead sheets and to gather them in balls of the size of a table tennis ball or tennis which one frequently finds on the Plage S.

Protection of the littoral

The dead sheets of posidonies are often brought back on the edges of beaches, where they pile up, forming compact and imputrescibles heaps sometimes. These heaps then prevent the erosion of sand by the waves. Nevertheless, like these beaches, naturally protected, are not favourable with the development of the Tourisme, the Municipalité S often make them withdraw, thus exposing the littoral to the whims of the sea. The posidonie belongs to five protected spaces on the French Mediterranean coasts, just like the black Oursin, the Grande mother-of-pearl, the brown mérou and the Cigale of sea.

Life cycle of the Posidonia oceanica

The posidonie, as all the plants with flowers reproduces by seeds.

The buttons appear in September, the flowers opening out in October and November. The Pollen is disseminated by the currents and will cling to the Pistil close plants.

The Fruit S are formed then in Hiver. In the month of May and June, they are detached from the plant. They resemble then, by the size, the form and the color, with a green Olive. They then will float during ten to fifteen days, with the liking of the current , then to rot and let escape a single seed which, while running, will germinate if the conditions of depth and basic allow it.

Nevertheless, this flowering and this fructification are seldom observed and the " mode; reproduction" privileged remains the propagation by cutting.

Synonym

Zostera oceanica L.

External bonds

(Indexed with a shell in the scientific name)

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