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
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
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
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
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
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
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
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
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
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
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
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