The "Posidonia oceanica" is an endemic plant in the Mediterranean with
roots, stalk, leaves and fruit that lives under water between the surface
and a maximum depth of some 40 metres. The plant forms fields of
posidonia, called also, seaweed fields, although they are not formed by
seaweed, that are the most important ecosystem of the Mediterranean, equivalent
to the forests of the land ecosystems.
It is thought that in the Balearics and Pitiüses, there are some
750 km2 of fields of posidonia situated on the sandy seabed and rarely
on rocky beds, that supply great quantities of oxygen and organic material,
contributing, also, to the balance of sediment on forming barrier reefs
that maintain the coastal stability and protect the beaches from erosion.
The fields of posidonia are also a great source of biodiversity as they
are the habitat of numerous vegetable and animal species, some of which
are in danger of extinction. The "Posidonia oceanica" has an annual
growth cycle and the dead leaves, sometimes in the form of a ball, are
deposited on the beaches, protecting it from the erosion caused by the
waves.
The seaweed fields of the Balearics are spread around many places. The
main concentrations are in Ses Salines in Eivissaand Formentera, south
of Formentera, Sant Antoni de Portmany in Eivissa, south of
Menorca, the bays of Alcúdia, Palma and Pollença on
Mallorca, and Cabrera. Although the scientific community has recognised
their importance to maintain the quality of the coastal waters and to form
and preserve the beaches, the seaweed beds are threatened, amongst other
causes because of the uncontrolled rubbish that contaminates the water,
the construction of ports, quays and dikes that originate changes in the
marine currents, the regeneration of beaches with extraction of sand from
the bed of the sea, illegal trawling fishing, non regulated anchoring of
boats and the introduction of exotic species such as the Caulerpa taxifolia.
Finally, we stress that in 1993 the Unesco declared Menorca a Reserve
of the Biosphere because of the important archaeological and natural heritage
it preserves, amongst which are the important seaweed fields. At
the same time, the fields of posidonia of the Natural Park of
ses Salines in the south of Menorca and north of Formentera, together with
other monumental places on Eivissa, such as the fortified
Dalt Vila, the
necropolis
of the Puig des Molins and the
Phoenician
village Sa Caleta, were declared in 1999 World Heritage by Unesco.
Photos ©
Biel J. Perelló
i Coll