Introduction of new species

Because the ocean shipping industry is international, new marine animals and seaweed from distance lands are occasionally transported by the ships. The introduction of a new type is almost always unintentional; it has attached itself to the rump of the ship or has accidentally landed in the ballast water. Sometimes foreign types escape from breeding farms, and end up establishing themselves. Between 1900 and 2000, more than 150 non-indigenous species were discovered in the North Sea. For the Northern German Wadden Sea, it was calculated that 5 to 10% of the animal species found there were non-indigenous. The newcomers are often damaging competitors for the indigenous species.

Chinese mitten crabs: brought in with trade ships in 1912, now commonly found.

Nowadays, seaweed and aquatic animals originating from places such as Japan, America and New Zealand can be found in the North Sea. On the one hand, the spreading of the number of types is interesting, however since the phenomenon is occurring on a world-wide basis, the differences in fauna between the different coastal environments is growing smaller. It is also possible that a newcomer pushes out an old indigenous species because the newcomer is better adapted to the situations under which the two types live. There are plenty of examples on land and in fresh water. The Pacific oyster (Crassostrea gigas) was released in the Oosterschelde and has spread out over a large area. Pacific oysters grow faster than the 'normal' oysters. Many German mussel banks are now colonized by this giant oyster. A new species of brown seaweed was also introduced along with the oyster.

The introduction of new species is not only damaging for the ecology, but for the economy as well. The dinoflagellates Gymnodinium and Alexandrium, originally from Southeastern Asia, are presently distributed practically throughout the world. Some species of dinoflagellates produce toxic materials which are harmful to fish, marine mammals and shellfish in mussel and oyster cultures. Because the poison accumulates in the shellfish, it can also be harmful for man.

The toxic algae Alexandrium: active in the North Sea region since 1965.

In early 1999, a new seaweed species for the Netherlands was discovered in the Oosterschelde. It has been named Japaj Wakame. The thallus ('leaf') can reach 2 meters in length. There is no Dutch name yet for this seaweed.

Other foreign types which have succeeded in establishing themselves here are: the Chinese mitten crab, the New Zealand barnacle (Elminius modestus), arriving in Europe with British warships in 1945; the Chinese mitten crab (probably landing in Europe in 1912), the rare North American blue swimming crab, the very well thriving American razor shell; Japanese sargassum, and the American piddock, which competes with the white piddock.

Vikings

The sand gaper is already an 'old new' inhabitant, probably the first species brought to our shores per ship. Up till recently, it was assumed that this shellfish was brought over from America in the 16th century. Recent finds show that this occurred even earlier: the Vikings seem to have introduced this animal to Europe halfway through the Middle Ages (shells have been found in Denmark dating back to 1250).

Marenzellaria bristle worms, which originated in North America, were first observed along the North Sea coast in 1983. Not long afterwards, they were found in massive numbers in the Baltic Sea. This species probably came with ballast water from ships. Scientist presume that Marenzellaria is a competitor for the indigenous ragworm Nereis diversicolor.

In May 1998, Danish fishermen caught large amounts of dead garfish in the North Sea, in Danish coastal waters and in the Skagerrak. The cause appeared to be a new harmful algae for the North Sea, Chatonella. This algae species originated in the seas around Japan. This species was accidentally imported to West-Europe in the 1990s, probably via ballast water from freighters.

The pencil-crab Hemigrapsus penicillatus from Japan is a recent import, first found in the Netherlands in April 2000. This five-centimeter large crab has plucks of hairs on its claws resembling hair of a paintbrush. It competes with the (much larger) shore crab for food. The pencil-crab probably came to the French Atlantic coast with a load of Japanese oysters in the 1990s. The distribution of the crab increases by around 100 kilometers per year!

Predator snail

The predator snail Rapana venosa was fished up off the coast of Scheveningen in 2005. this snail originated in Japan and China, can grow between ten to twenty centimeters. It eats bivalves such as oysters and mussels. In the 1950s, the snail slaughtered these shellfish in the Black Sea. It is not clear whether or not this snail is spreading out in the Netherlands.

Weblinks

Database with information on exotic species in Europe:
http://www.zin.ru/rbic/

Source: de Vleet, Ecomare