Aliens on the shores

In the early 1980s, a biologist at the tropical aquarium in Stuttgart, Germany, noticed that the beautiful green alga Caulerpa taxifolia (Fig. 1) would make an ideal aquarium decoration. It does not wither, it is fast growing and it withstands cool temperatures. In the following years, many aquariums acquired Caulerpa plants from Stuttgart, among them the Oceanographic Museum of Monaco, from which it escaped into the Mediterranean Sea. In 1984, the alga covered an area of around 1 m2 on the coast of Monaco. Since then, it has invaded large areas of the French and Italian coasts and has spread as far as the coasts of Spain, Croatia and North Africa. The alga grows everywhere, from the surface to the lower limits of underwater vegetation, forming huge monocultures that displace other plant species and, being highly toxic to many fish species, also threatens aquatic fauna wherever it roots.