Japanese sargassum grows quickly and massively, causing lots of problems in harbours (jammed screws), on beaches (stink inconvenience when it dies) and for those that use seawater (cool-water admission, saltwater aquariums). Just like the name indicates, Japanese sargassum comes from Japan. Scientists think that it arrived in the North Sea via Japanese oysters and attached to ships. At any rate, it has been present in the North Sea region since 1973. Because this species contains many small gas bladders, it is not uncommon for plants to lift up their stony base and drift to other places.
Scheepsschroeven lopen vast, zeewaterinlaten en aquaria groeien dicht, en hopen wier liggen te rotten op het strand. Veel mensen hadden liever dat dit wier in Japan was gebleven, maar ja, het is door mensen ingevoerd, waarschijnlijk met transport van oesters. Japans bessenwier is sinds 1973 in de Noordzee aanwezig en sinds 1980 ook in de Nederlandse wateren. Het wier komt vooral veel voor langs rotskusten. Het Japans bessenwier kan enkele meters lang worden. Grote planten kunnen, als gevolg van hun drijfblazen, de stenen waar ze aan vastgehecht zijn optillen en verplaatsen.
A large brown seaweed (with a frond often over 1m long), the stem has regularly alternating branches with flattened oval blades and spherical gas bladders. It is highly distinctive and olive-brown in colour. Wireweed is an invasive species from the Pacific that appeared on the Isle of Wight in 1973, having spread to Britain from France. It competes with native species such as seagrasses and is considered a nuisance in harbours, beaches and shallow waters.Sargassum muticum is also known as 'Japweed' and 'Japanese weed'.
Grows on hard substrata in shallow waters and can also tolerate estuarine conditions. It can out-compete local species because it is fast growing, can reproduce within the first year of life and being monoecious can fertilize itself.
Sargassum muticum, commonly known as the Japanese wireweed, is a large brown seaweed of the genus Sargassum. It grows attached to rocks by a perennialholdfast up to 5 cm in diameter. From this holdfast the main axis grows to a maximum of 5 cm high. The leaf-like laminae and primary lateral branches grow from this stipe. In warm waters it can grow to 12 m long, however in British waters it gives rise to a single main axis with secondary and tertiary branches which are shed annually. Numerous small 2-6 mm stalked air vesicles provide buoyancy. The reproductive receptacles are also stalked and develop in the axils of leafy laminae. It is self-fertile.
Originally from Japan, by 1995 it had been found in Strangford Lough, County Down, Northern Ireland, this is an extension of the distribution of this invasive species. Herbarium specimens are now stored in the Ulster Museum (BEL catalogue numbers: F11241 - F11242; F11182 - F11185). By June 2009 it has become widespread in Ireland. The species was first found in the British Isles in the Isle of Wight in 1973. It is thought to have gained worldwide distribution through being transported with Japanese oysters (Crassostrea gigas). There is much concern about its impact on the coastal environment. It has become a nuisance forming large detached mats, clogging marinas, recreational areas and other sports facilities. It can foul fishing lines, clog pipes of boats and trap debris.
The species is particularly tenacious with fast growth rates, high reproductive rates and an ability to spread vegetatively.