Biodiversity & Conservation

Knotted wrack - Ascophyllum nodosum - General information

Ascophyllum nodosum

Image Keith Hiscock - Isolated growth of Ascophyllum nodosum on rock. Image width ca 60 cm.
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Distribution map

Ascophyllum nodosum recorded (dark blue bullet) and expected (light blue bullet) distribution in Britain and Ireland (see below)

Why do the maps differ?

Sightings Have you seen Ascophyllum nodosum?
If so please submit your record.

  • WC_Act_1981
  • UK_BAP

General information

Key Icon Researched by: Jacqueline Hill and Nicola White Text page icon Refereed by: Dr Dagmar Stengel

Taxonomy icon Taxonomy

Phylum Ochrophyta Brown and yellow-green seaweeds
Class Phaeophyceae
Map icon Recorded distribution in Britain and Ireland All coasts of Britain and Ireland.
Habitat information icon Habitat information The species attaches to rocks and boulders on the middle shore in a range of habitats, from estuaries to relatively exposed coasts. It occupies a similar shore height as Fucus vesiculosus. Subtidal populations have been reported, for example in the very clear waters of Rhode Island, USA. However, an intertidal habit is more usual.
Text page icon Description A common large brown seaweed, dominant on sheltered rocky shores. The species has long strap like fronds with large egg-shaped air bladders at regular intervals. The fronds of Ascophyllum nodosum are typically between 0.5 and 2m in length. The species often bears tufts of the small reddish-brown filamentous epiphytic algae Polysiphonia lanosa. Ascophyllum nodosum occurs on the middle of the shore, often with Fucus vesiculosus. The species grows slowly and plants can live to be several decades old. Individual fronds can become up to 15 years old before breakage.

This review can be cited as follows:

Jacqueline Hill and Nicola White 2008. Ascophyllum nodosum. Knotted wrack. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 20/05/2013]. Available from: <http://www.marlin.ac.uk/speciesfullreview.php?speciesID=2632>