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Knotted wrack (Ascophyllum nodosum (Linnaeus) Le Jolis) is a large, common, brown, edible seaweed of the northern Atlantic Ocean. It is a common species on the north-western coast of Europe (from Spitzbergen to Portugal) including east Greenland, and the north-eastern coast of North America.
It has long fronds with large egg-shaped bladders at regular intervals. The fronds can reach up to 2 m in length and are attached to rocks and boulders by a holdfast. The seaweed grows quite slowly and plants can live to be several decades old and take approximately five years to become fertile.
The species is found in a range of habitats from sheltered estuaries to moderately exposed coasts and often dominates the inter-tidal zone (although sub-tidal populations are known to exist in very clear waters).
Ascophyllum nodosum is harvested for use in alginates, fertilisers and for the manufacture of seaweed meal for animal and human consumption.
There are free floating ecads of this species such as Ascophyllum nodosum mackaii Cotton, which is found at very sheltered locations, such as at the heads of Scottish sea lochs and Ireland.
It has been recorded as an accidental introduction to San Francisco, California, and eradicated as a potential invasive species there.
References
Gibb, Dorothy C. 1957. The free-living forms of Ascophyllum nodosum (L.) Le Jol. J.Ecol. 5 : 49 - 83.
Miller, A.W. 2004. A new record and eradication of the northern Atlantic alga Ascophyllum nodosum (Phaeophyceae) from San Francisco Bay, California, USA. J. Phycol. 40: 1028 - 1031.
External links
"Knotted wrack"