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Island Ecology

Island Ecology

by José P Ribas

Posidonia Oceanica
The Gift Of A God


Ibiza Ecology

Have you any idea what is at the bottom of the sea round here?

It is as important to nature as the coral reefs off Australia.

It's to do with the salt and the sunlight and it couldn't happen anywhere else.

And now it's under threat.

"Posidonia Oceanica" is an endemic Mediterranean Phanerogam plant (a complete plant, like grass with flowers) of the "Potamogenotonacea" family, which lives in salty waters on the seabed, almost as deep as light can reach.

It's at its best from three to twenty five metres where the temperature zooms from 15 to 20c.

It's a plant, a rhizome with little roots, 10-15cm long, that fix it on the seabed. The stem has six to ten thin, long; slightly curly leaves, ribbon-like, standing up proudly.

They are about three feet long with four to ten hermaphroditic flowers in an ear. The fruit is like a drupe and is the size and the shape of an olive that floats for a time and can start new colonies miles away from the original plant.

The "Posidonia" - for a long time considered as "algae" and called by the same name by the natives - colonises the seabed, especially in the sunny and sandy areas, that - with time - transforms into wide prairies. The Balearic Posidonia meadows have proved to be (by the carbon 14 test) 4,000 years old, becoming one specific habitat and complete ecosystem.

The ecological importance of these wide prairies for the life of the entire Mediterranean area is (or was) to be compared with the Coral Reefs of the Australian Eastern Coast, spread all along the islands and Mediterranean coast, doing a similar function as the reefs do. It's the birthplace, the berth place, the nursery and habitat for hundreds of species, the first loop of life's chain, producing great amounts of zooplancton and fitoplancton.

This abundant variety of life attracts hundreds of other species that feed themselves in these areas, from micro-organisms to birds, men and the Mediterranean whales.

Recent studies done by the Catalan sea-biologist Manu San Felix in the best meadows, also show that in the Spring the seventy cm. long leaves of its 700 stems by square metre, with the solar radiation, (photosynthesis) produces the extraordinary amount of 21 tonnes of oxygen per hectare per day (the European forests produce about 12 tonnes per day).

So we can also speak of the Posidonia meadows as the Mediterranean's proper lungs. Further studies will prove the relationship of this plant and the temperature of the area, as well as the importance of it in all the process of transforming the seawater into sweet water inland.

All year long the plant produces new leaves and loses some, but - by the end of the summer - the Posidonia starts losing massively its yearly autumn leaves. After being used as substrate and aliment for several species of small creatures, every leaf is a big community by itself (hidrozous, poliquets, foraminifers, mollusc, crustaceans, isopodes, tiny algae etc.) that degraded part of its lignin and tannins, meanwhile the new leafs are born at the centre of the stem.

The dead leaves go to deeper waters, to be degraded by bacterias, creating a new life cycle. The rest are brought to shore by the first winter storms, thousands of tonnes piling up on the beaches, sometimes up to two metres. But this is not the end of the function of this amazing and profitable plant.

Locals used to collect part of this yearly harvest, going down the beach with carts and horses, to be used later on, after being left over a year in the open air to dry and for the rain that washes away a good part of its salt.

Afterwards it will be used as a bed for the animals, becoming first class manure. It was also used for house roofing by Ibicencos.

Mattress were made of these leaves and it was well used in packaging for fragile materials (in Spanish we have the common name of "alga de vidrieros" - "glass- maker seaweed").

On the island of Mallorca, there is still an active market for this product. It also takes a part in some ceramic processes (as fossil clay) because of its high content of silica. This is still done in Formentera by the local ceramists.

Nowadays it is also being prescribed for therapy, by sunbathing on a bed made with its leafs down by the shore. I don't know what it cures, but it is more comfortable then lying on the rocks.

By the seashore, the dead leaves form layers with the sand, so it becomes a barrier that protects the coastline from erosion and the sand on the beach from being washed away by the sea-storms. On the beaches that the Posidonia does not get "clean" there is no need to replace the sand.

It helps to increase and fertilise the dune-system by the beach, creating a new vegetal barrier, behind the dunes; the littoral forest can start growing, sheltered from the strong sea-winds.

We cannot take apart these four elements: without the Posidonia meadows, there would be far fewer and smaller sandy beaches. Without the sand and the dead Posidonia leaves, there would be no dunes with vegetation and no forest behind them. The erosion elements would be far more severe and the entire littoral would be much more arid like a desert.

And that seems to be the way we are going.

The "Posidonia Oceanica," a gift from a God, is retiring to the "Olympus" to meat her creator, "Poseidon."

"God of the Seas, Lord of the Tempest," who named and blessed his best creation as a well-beloved daughter, leaving her on Earth, for the Glory of his name and the Joy of Humankind, when he was no longer needed as a God and was sent back to the "Olympus" by another God.

The problem is that it took a long time for us to realise the importance of this plant and all the processes involved in it.

It's only in the last two decades that the alarm has gone off, though the problem was detected long ago, especially by biologists, fishermen and sailors.

By then, the "Posidonia" meadows had already suffered drastic reductions, even despaired in most of the areas that used to be its own realm.

"Posidonia" needs a good amount of light, steady salinity and temperature it doesn't tolerate pollution. Yet the Mediterranean is becoming one of the most polluted seas in the World, especially by the coast where the plant lives.

The big increase in industry, in all the countries of the littoral, the new sailing marinas, the population and the millions of tourists that comes to its shore - more every year - have become more then just a threat .Not just for the "Posidonia meadows," but for all the life in the sea.

In the early 1990s, the Spanish government developed laws to reduce the fishing and other activities in the prairies, but the non-stop aggression carries on.

Every day hundreds of boats anchor and fish illegally on them.

We need to change our mentality about this plant.

There are people going to a "Blue Flag" beach, carrying a big plastic bag full of plastic things that they don't mind leaving anywhere. And afterwards they complain about the beach being filthy, dirty with the amount of seaweed by the shore.

It could not be a better way to prove the great quality, health and vitality of the seabed, the water and the beach. If this happens, maybe it will be best if everybody could understand this fact.

At last the Balearic "Posidonia" meadows, over 88,000 hectares altogether - still the best and almost the last ones left in the Mediterranean Sea - have been declared "Patrimonio de la Humanidad" by "UNESCO" and new strategic plans for the preservation of this priceless and fragile treasure are being developed.

The Good News

Is there any? In the middle of August, in Ibiza? You must be joking!

Oh, yes. Sorry! There is overbooking in the hotels, and super-overbooking in the discotheques. You have to wait five hours for a taxi and still it doesn't come. There are no cars or anything for renting for the next two weeks. All around the Island there are so many boats anchoring that the sea level has risen up at least a foot over the limits of what it is supposed to raise by the end of this century. All this has to be good news. For some.

To know more about "Posidonia Oceanica":

Manu San Felix: La Posidonia. El bosc submergit. (2000) Cuaderns de Natura de las Balears.

Boudouresque, Ch. F. Découverte de l'herbier de posidonie. (1983)

Les especés marines á protéger en Mediterranée. (1991)

José P Ribas