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Dieren en planten

Water en land

Mens en Milieu

Japanese sargassum


thready, bushy, branched


up to some meters



Introduction in North Sea area:

1973 (England)

  • Dut: Japans bessenwier
  • Lat: Sargassum muticum
  • Eng: Japanese sargassum, japweed, wireweed
  • Ger: Japanischer Beerentang
  • Dan: Sargassotang
Japanese sargassum, foto fitis, sytske dijksen

Japanese sargassum

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. 

  • Washed ashore

    It is seldom that entire Japanese sargassum plants to wash shore. Usually, only the ends are found. However in this photo, you see the tip of the plant above and the base below. This entire plant was more than one meter long. The top part contains 'berries' (gas bladders) and small leaves. The base has larger leaves and no berries. This seaweed is usually found along rocky coasts. Strange enough, in Japanese waters this seaweed doesn't grow longer than a couple of meters. However in European waters, it grows quickly and long: as much as 10 cm per day and up to 16 meters long!