Posidonia oceanica forms extensive seagrass meadows around the Balearic Islands, known as underwater forests, with high biodiversity of species and their role in the ecosystem is of great importance.
Seagrass meadows provide shelter for many species; produce oxygen on a daily basis, removing carbon dioxide from the atmosphere and creating tons of biomass per year. Likewise, they act as barrier reef structure, which, although they are scarce today in the Mediterranean, have a high importance and longevity.
Seagrass meadows maintain the coastline and protect our beaches from erosion, in Winter, the accumulation of the leaves on the beach, called “banquettes”, stabilize the bottom and reduce the effect of the waves on the coast. In addition, the shells of the epiphytic calcareous organisms of the posidonia leaves are integrated into the accumulated substrate, generating whiter beaches.
One of the peculiarities of Posidonia is its tolerance induced by climate clange, acting as an excellent indicator of the quality of the waters. Since 1992 it has been considered a habitat of priority interest to the EU, and is currently regulated by different regulations.
However, despite Posidonia is being protected by different regulations, unfortunately it is also a threatened. The increase in activities in Balearic waters is endangering the conservation status of Posidonia through direct impacts such as anchors, uncontrolled anchoring of boats, as well as many other threats. Faced with this situation, the Balearic government approved Decree 25/2018 of July 27, aimed at the conservation of Posidonia oceanica, to make the development of human activities compatible with the protection of the species and its habitat.
In summer, the meadows have the highest organic activity and they are filled with epiphytes and small microorganisms. During this process and with higher temperature on water, the plants acquire a whitish and brownish tone, especially in the shallower areas.
Flowering occurs in late autumn. The inflorescences develop in a few days. Grasslands, like deciduous forests, renew their leaves every year. This process, although it occurs from January to December, is more evident in the fall, since it is in this season when the storms tear off many leaves and accumulate the fallen remains on the beaches.
At this time is when the growth of the new leaves is slower, coinciding with the lowest temperatures of the year. Flowering continues and at the end of winter the first fruits can be seen
In Spring, the ripe fruit is released from the plant and floats adrift for a few days. The seeds are dispersed far, following the currents. After hours or even days, they open, releasing a single seed that falls to the seabed, where it germinates and creates a new plant.
At first glance, seagrass on beaches seems like an annoying impurity, but sand and seagrass on the Balearic Islands form an inseparable whole. Posidonia benefits the sand to grow and the dune systems are maintained, in good part, thanks to the Posidonia
For years, Posidonia has had different uses: medicinal, agricultural, for construction, etc. let’s see the best known:
In recent years, scientific studies aware that Posidonia meadows are being seriously damaged by human action. Marine pollution derived from outfalls and discharges, along with indiscriminate anchoring, are some of the factors that make grasslands are declining.
Likewise, the Balearic Islands receive a high number of tourists each year and each summer season they face the large influx of pleasure boats who want to enjoy their waters, therefore, among the pressures mentioned, it is worth highlighting the incorrect anchoring of vessels.
Impact on Posidonia meadow during the anchoring manoeuvre and lifting the anchor back: sometimes it is not easy for managers to see the seabed from the boat and distinguish the presence of Posidonia. Aspects such as the lack of light, the sunset or the turbidity of the waters, prevent the anchoring from being carried out in the correct areas, such as the sandbanks, without Posidonia.
Impact on Posidonia oceanica beds because the anchor chain is not in a vertical position: friction and movement of the chain gradually degrades the meadow.
To solve this and other problems; In addition, to prevent the deterioration of Posidonia, the Balearic Government approved decree 25/2018 of July 27, which establishes a framework for the protection and conservation of Posidonia oceanica
In order to apply this Decree efficiently, it is necessary to know exactly where the Posidonia oceanica is.
For this, the surface of the seabed between 0 and 30 meters deep has been studied in order to have an Atlas of Posidonia that can serve as a useful tool.
Govern de les Illes Balears, Conselleria de Medi Ambient, Agricultura i Pesca, Direcció general d’Espais Naturals i Biodiversitat
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