Seaweed
"Seaweed" is a colloquial term and lacks a formal definition. A seaweed may belong to one of several groups of multicellular algae: the red algae, green algae, and brown algae. As these three groups do not have a common multicellular ancestor, the seaweed are in a polyphyletic group. In addition, some tuft-forming bluegreen algae (Cyanobacteria) are sometimes considered to be seaweed.
Caulerpa taxifolia
It is thought that the seaweed was accidentally released into coastal waters of the Mediterranean Sea (just below Jacques Cousteau's) Oceanographic Museum of Monaco in 1984. Ten years later, the claim was made that "Caulerpa" had grown to cover , and was preventing native plants from growing. This concern earned the algae the dubious nickname "Killer Algae" after the title of a book written on the subject. Its author, Marine biologist Alexandre Meinesz first discovered the alga in the 1980s, and requested the help of the Monaco Oceanographic Museum, which sat right next to the first known "C. taxifolia" patch. The director of the museum argued that this invasion probably happened naturally, the result of ocean currents carrying a tropical species into the area. The parties bickered publicly for years over whether the species was natural or invasive, and whether the museum had released it or not, at the expense of sound scientific research on the species and its ecological significance.