|
|
|
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.
|
|
Page 8
of 9
|
|
|
