Algae, Morbihan, France

For more than a century, oyster farms have been the privileged sites for the introduction of “exotic” species. In the 1920s an epidemic decimated Crassostrea angulata, the most widely exploited oyster species in France. A Japanese species, Crassostrea gigas, was then introduced—and, involuntarily along with it, some thirty species of animals and algae that today live in the waters of the English Channel and the Atlantic Ocean. One example is the Sargasso (Sargassum muticum), a brown algae, seen here in the Gulf of Morbihan, where it has become a part of the local flora. It was feared that there might be a galloping invasion, but this species, while becoming abundant, seems to have found its place in the ecosystem. Nevertheless, its proliferation and gigantism, capable of disturbing aquaculture and causing competition to the detriment of local species, require careful watching.