An invasive or introduced species is a species of animal or plant which has been introduced either directly, or indirectly, into a region where it is not indigenous and has naturalised itself to the extent that it no longer requires human assistance or cultivation to survive.  Its subsequent reproduction can then threaten the survival of indigenous plants and animals in that region.

It is thought that invasive species are one of the major causes of mass-extinctions of native fauna and flora. 

The most publicised “invasion” of recent years in the Mediterranean is surely that of Caulerpa taxifolia, the highly-invasive marine algae or seaweed which was first documented off the French Mediterranean coast in 1984 and has since spread like wildfire, smothering everything in its path, competing for sunlight and nutrients and posing a severe threat to other marine plants and wildlife.

It is thought that taxifolia most likely arrived in the Mediterranean Sea via contaminated water released from an aquarium.  In 1993 an Arrêté issued by the French Ministry of the Environment stipulated that it is forbidden to sell, buy, use or reject any part of this seaweed into the sea.  Regardless of that, until fairly recently taxifolia was still being sold in aquarium shops in the PACA region.

Invading species are classified according to the frequency of their apparition on the territory.  Species classed as “major” invaders along the Mediterranean coast include Acacia dealbata, the “florists’” Mimosa, which has practically taken-over certain areas of the Var.  In an attempt to stabilise the spread of this species in the wild, authorities in Provence have been systematically cutting them down and replacing them with indigenous species, such as Laurier and Caroubier.  There are also “emerging” invaders which are considered to be the “major” invaders of the future and species which are “under surveillance” with special attention being paid to certain populations.

Many invasive plant species have been imported into France as garden plants and often exotic insects have hitched a free ride on their host plants.  Such is the case of Cacyreus marshall, a butterfly native to South Africa, the caterpillars of which feed on geraniums and pelargoniums. This insect is thought to have arrived in Europe ten years ago, in the form of caterpillars or chysalides hidden amongst imported plants.

Another relative newcomer which is making its presence felt is Rhynchophorus ferrugineus, the red palm weevil, which attacks palm trees.  Originating from the tropics, this insect was probably imported into Spain during the Universal Exhibition in Seville in 1992 and was first recorded in the Var, at Sanary sur Mer, in October 2006.  Other recent discoveries of invasive species in the Var include Cochylis and Eudemis, butterflies which are known commonly as “vers de la grappe” (grape worms), which attack vines and are capable of ruining a crop.

Whilst the importation of live plants may have allowed the inadvertent introduction of certain invasive species, who could have guessed that when the US Army landed in Provence in 1944, their cases of ammunition were harbouring a parasitical fungus called Ceratocystis fimbriata which kills plane trees in two months flat?  To date, this fungus has killed around 40,000 plane trees in Marseille alone.

In the Mediterranean, there is a specific vector of introduction of species from the Red Sea, which is via the Suez Canal.  It is thought that certain molluscs and jellyfish have hitchhiked their way into the Med. by clinging to ships’ hulls or stowing-away in their ballast tanks.  Other species have just swum straight through, such as Carcharhinus melanopterus, or the black-tip reef shark, which is classed as a “new” species in the Mediterranean Sea.

Climate change may make it easier for exotic invasive species to flourish but the fact remains that many plants and animals are highly-adaptable.  If we leave the proverbial door open, the likelihood is that potentially invasive species will be quick to move in and several already have.

Article from The Riviera Reporter Var Supplement, issue August/September 2007

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