polmarcom2.jpg (12647 octets) Biological pollution

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        The Caulerpa taxifolia appeared in the Mediterranean in 1984, it became since the alga star in the ecological headings of the medias. This alga of a beautiful dark green was of ten used in the ornament of the aquariums. In 1984, it is located for the first time at the foot of the oceanographical museum of Monaco.  In 1989, Alexandre Meinesz makes the first studies on this alga. According to him, the alga would have become Mediterranean after the accidental draining of an aquarium of the museum of Monaco in the sea. How ever this assumption was never proven.

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        One can find it surface until a 100 meters depth. It develops on all types of substrates.   In 1990, it covered three hectares; one estimated, in 1992, who the surface which it occupied was of more than one hundred hectares. In 1994, it occupied more than 20 times this surface and in 1996, it had colonized more than 1500 hectares and no one does not know how to stop the progression of the caulerpa. In addition, it is supported by the lack of spirit of the natural brouteurs allotted to the presence oftoxin synthesized by the alga.

        The impact of the caulerpa on the ecosystem of the Mediterranean is considerable. Several vegetable species live on the Mediterranean littoral and play for the majority a well define drole in the food chain. How ever this alga induces a strong reduction in the biodiversity in the colonized mediums. Since 1991, one noticed that it had covered with the herbaria with Cymodocea nodosa and especially with posidonie. The herbarium with posidonie initially seems well to react in contact with the alga, by increasing its production. Then, completely invaded once, it shows signs of stress (falls of the sheets...) which led to a regression then with the total disappearance of the herbarium as wellas the algae pushing on the posidonies.

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Despite several years of search any effective means was not still found to limit the expansion of the caulerpe. Only there peated manual pulling up campaigns give results. But, in spite of these campaigns, the alga pushes back in a few weeks with a very fast growth of a few centimeter per day.


The sartgassum muticum

It's an endemic alga of Japan more known under the name of " giant sargasso ". This brown alga was found for the first time in 1973 on the English coasts and 1975 on the French coasts. Since, it is rependue everywhere of Norway in the Mediterranean. One finds it up to 20 meters of depth in settlements which can sometimes be very dense. It became the source of multiple ecological harmful effects. From its big size, it covers surface with water and asphyxiates the other close algae.



      These two examples of algae are revealing the often irreversible ones and sometimes vermin with the ecosystem of the zones which they invade. In 1990, being given the broadth of the biological invasions and the consequences which they involve, the international consulting for the browsing of the sea enacted a " code of good control " to reduce the introductions of marine species.

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Lettre.gif (4085 octets) - créé le 12/04/2000