Posidonia oceanica (commonly known as Neptune Grass or Mediterranean tapeweed) is a seagrass species that is
endemic to the Mediterranean Sea. It forms large underwater meadows that are an important part of the ecosystem.
The fruit is free floating and known in Italy as 'the olive of the sea' (l'oliva di mare).
Balls of fibrous material from its foliage, known as egagropili, wash up to nearby shorelines.
http://en.wikipedia.org/wiki/Posidonia_oceanica

On the beach there were a lot of those round things, made up by fiber of something.
We wondered from where it came.
We still do. But they were everywhere on the beach.
That's what we wrote when we were down there. Coming home we learned more.

The balls, or aegagropiles, are actually composed of the fibrous remains of Posidonia oceanica.
Over time, dead fibrous tissue of individuals of this species are tossed about by waves.
The constant rolling action of the sea eventually forms this material into balls which wash up on the beach.
http://www.ubcbotanicalgarden.org/potd/2008/02/posidonia_oceanica.php



The oceanic Posidonia 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 prairies 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.


Posidonia oceanica
This photo is selected for Google Earth [?] - ID: 51093059

It is thought that in the Balearics and Pitiüses (Pine Islands, south of Ibiza), there are some 750 km2 of prairies 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 oceanic Posidonia 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.

We have been told that recently (October 2011) parts of some of the largest beaches here disapperadduring a storm.
Hard to believe, but we experinced the same on La Gomera in the Canary Islands:

2001 - a beautiful sandy beach 2005 - day before day after - and nobody could understand what had happened to their lovely sandy beach.....

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.


Caulerpa taxifolia.
Photo: National Oceanic and Atmospheric Administration, USA (public domain)

It is thought that the seaweed was accidentally released into coastal waters of the Mediterranean Sea just below
the Oceanographic Museum of Monaco in 1984. Ten years later, Caulerpa had grown to cover 7,400 acres (30 km2),
preventing native plants from growing[citation needed] and leading to the nickname "Killer Algae".
Caulerpa overgrows the seabed and disrupts the food cycle dependent on the native plant life
http://en.wikipedia.org/wiki/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.
http://www.eivissaweb.com/reports/natural-areas/prairies-of-oceanic-posidonia/3/#inicicont

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