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Origin and distribution
Japweed has its origins in Japan where it grows together with 27 other
closely related specie in coastal waters that are effected by warm oceanic
currents. The Sargassum-family has spread worldwide and most of
the related specie have never been in contact with the Sargasso Sea, where
the masses of alga comprise mainly of two specie, Sargassum natans
and Sargassum fluitans. It is not unique to find Sargassum-specie
in Europe. 3-6 specie are found growing naturally in the Mediterranean.
During the 1940´s, japweed was found along the west
coast of North America, probably as a result of the earlier imports of
the "giant
japanese oyster". It is believed that japweed originated from spores
or small plants on the shells of the oysters. At present, the alga has
spread from Alaska to Mexico.
After adult "giant japanese oysters" were introduced to France,
drifting examples of japweed were first
discovered in 1971 outside Portsmouth in England. Two years later,
an attached population was found off the Isle of Wight. Since then, japweed
has spread along the coasts of Europe and to the Mediterranean. In the
Limfjorden (Denmark), japweed was discovered in 1984, for the first time
in Scandinavian waters. Here, dense populations up to 2m in length were
present from the surface and down to about 2m. These populations were
best developed amongst the bladder
and toothed wracks
at depths of between 0,5-1 m. Even along the west coast of Jutland several
finds have been made. During 1992, the first attached examples were found
in the Danish area of the Kattegatt. Along the south coast of Norway,
the first drifting examples were found in 1984 and it was not until 1988
that the first attached examples were noted. Japweed is now found along
the whole of the Norwegian south coast.
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