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Newcomer in our waters
Codium fragile is a
relative newcomer to swedish waters - it was first noticed
after the First World War - and is noticable because of its
clear green colour. It is a member of the green algae order
caulerpales, that has many members in tropical and
sub-tropical waters, and also a few in colder regions.
In Bohuslän on the Swedish west coast, two sub-species of codium
fragile have been found. With the sub-species tomentosoides, the
surface cells are relatively long and carry
a long thorn, while with scandinavicum, the surface
cells are relatively short and devoid
of thorns. It is believed that this specie may originate Vladivostok.
This specie is also known as C. dichotomum. Identifying these specie
is difficult, as there are many intermediate species. The sub-specie scandinavicum
grows to about 10-20(-30) cm, with dense branching (7 times), quite often
possessing a series of short, angular shoots.
The sub-specie scandinavicum was first discovered in Bohuslän
in july 1932 at a depth of 1-2 m on a wall at Själholmen just outside
the Gullmarsfjord. In similar localities, large rock
pools, it became so common that fears were raised that it may force
out the original vegetationen. But the algae retreated. It appears to
have good
and bad years. The codium-invasion occured at the same time as the
"eel grass death", when large areas once occupied by eel
grass (Zostera marina) were drastically depleted along the
coasts of Europe. Codiums most southerly distribution along the Swedish
coast is not known. On a map of the species distribution created in 1948-50
by the Norwegian Egil Moss, no notation south of the Gullmarsfjord was
made.
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