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Assessment of risk and risk-reducing measures related to the introduction and dispersal of the invasive alien carpet tunicate Didemnum vexillum in Norway.

Academic literature review
Year of publication
VKM Report
External websites
Involved from NIVA
Paul Ragnar Berg
Johanna Järnegren, Bjørn Gulliksen, Vivian Husa, Martin Malmstrøm, Eivind Oug, Paul Ragnar Berg, Anders Bryn, Sonya Rita Geange, Kjetil Hindar, Lars Robert Hole, Kyrre Linné Kausrud, Lawrence Richard Kirkendall, Anders Nielsen, Brett Kevin Sandercock, Eva Bonsak Thorstad, Gaute Velle


Didemnum vexillum is colonial sea squirt, a marine species which originates from the northwest Pacific; it was first recorded in Norway in November 2020. Didemnum vexillum is an alien species, meaning that it is a species that has been transferred from its original region to other regions of the world through human activity, and it had not previously been recorded in Norwegian waters. The species is regarded as having great invasive potential and having strong negative ecological effects on biodiversity. It is also considered to pose a risk to marine industries such as shipping and aquaculture, with possible major negative economic impacts.