Is the Killer Alga that Deadly?

The discovery of the tropical alga Caulerpa taxifolia in the Mediterranean Sea, at the end of the '80s, triggered a great warning signal. The "killer alga" was declared "harmful for the Mediterranean ecosystem", and its rapid reproduction an "ecological catastrophe". The alga appeared to have escaped from the Monaco Aquarium.

The next decade meant a fearsome fight against the killer alga: weeding out campaigns, salt spreading (an aberrant solution) and the use of hot water jets. It was said, without much scientific support, that this alga was toxic both for the fish and people, because of its toxins (especially caulerpenine) and its proliferation would have put in danger the Posidonia (sea grass) fields, important for the ecological balance of the Mediterranean.

But more recent researches show that, accidentally or not, the alga seems to have rather entered Mediterranean through the Suez Canal coming from the Red Sea. In the end, about 300-500 of the species (mainly fish, crustaceans and algae) existing in the Mediterranean Sea have come from the Red Sea; less species enter Mediterranean coming from the Atlantic through the Gibraltar Strait. 20 % of the Mediterranean fish are tropical (110 species compared to 530 "indigenous" species).

In fact, at the beginning of the '20s, another related alga invaded the French Mediterranean: Caulerpa prolifera. In 1976, the area of the Sidney harbor (Australia) was invaded by Caulerpa filiformis, which replaced a Posionia type. More dangerous and aggressive seems to be Caulerpa racemosa, an alga that invaded in just two years the surroundings of the Genoa harbor (Italy), over a surface of 800 hectares, reaching Livorno. Biologists debated whether to introduce or not exotic snails to hamper the spread of the algae, but it resulted that the plant was consumed by a Mediterranean snail, Oxynoe olivacea. In the end, more media show than real danger in the case of Caulerpa algae. Or not?