Picture of
Our largest alga

Perennial primary shoots


Summer and winter appearance


Origin and distribution

Japweeds journey to Sweden

Establishment in Sweden and Denmark

Establishment and development in the Koster area

Development along the Swedish west coast

Development along the Swedish west coast

The results from a survey of the geographical distribution of the brown alga, japweed, from a number of areas along the Swedish west coast in 1996 are described on the following page. Besides data showing distribution, information pertaining to population size and plant substrate has also been collected. The results have been compared with a similar survey conducted in 1993.
   Attached plants have been observed from the Norwegian border and south to Träslövsläge in central Halland, which represents an expansion of about 100 km further south during the period 1993-1996. The plants in the southern waters were fertile and showed differences in appearance when compared with material from Bohuslän further north.
   During the initial establishment phase, it was primarily areas in the outer archipelagoes that were colonised by japweed. The plants have since 1993 spread further into the archipelagoes, but information about colonisation of the water systems around the large islands of Orust and Tjörn is still scarce. In the southern areas of the Gothenburg archipelago, the number of sites and individuals is still low, even if the number of sites has dubbled.    Along the coast of Halland it has been shown that distribution is very irregular, with areas in north where japweed has not been observed, which is in marked contrast to the heavy colonisation around the Värö peninsula. Around the cooling outlets from the Ringhals nuclear power plant is found the most dense and vigorous population in Sweden. In 1996, large quantities of drifting plants were observed in the waters around the Värö peninsula and the established population is a source for colonisation for the rest of the Halland coast.
   The occurrence of japweed and its expansive growth along the Swedish west coast constitutes the most dramatic and striking change within the seaweed belt in modern times. Japweed has established itself and has became a permanent member of our coastal fauna. As yet, little is known about the effects (short and long term) of this colonisation, how other organisms are knocked out because of competition, which areas stand in line to be colonised next and if this species is a threat to the Baltic. 

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Bo Johannesson | Martin Larsvik | Lars-Ove Loo | Helena Samuelsson