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