Ascophyllum nodosum

Ascophyllum nodosum is a large, common, brown alga, in the Class Phaeophyceae. It is an edible seaweed of the northern Atlantic Ocean, known as knotted wrack or egg wrack. It is common on the north-western coast of Europe (from Svalbard to Portugal) including east Greenland and the north-eastern coast of North America.

Ascophyllum is very popular amongst the science community and has been claimed to be both the most active seaweed on the planet as well as the most researched by the academic community.

Description and ecology
Ascophyllum nodosum has long fronds with large egg-shaped air-bladders set in the fronds at regular intervals and not stalked. The fronds can reach 2 m in length. They are attached by a holdfast to rocks and boulders. The fronds are olive-brown in color and somewhat compressed but without a mid-rib.

This seaweed grows quite slowly and can live for several decades; it may take approximately five years before becoming fertile.

Life history is of one diploid plant and gametes. The gametes are produced in conceptacles embedded in yellowish receptacles on short branches.

Ascophyllum nodosum is found mostly on sheltered sites on shores in the mid-littoral where it can become dominant species in the littoral.

Polysiphonia lanosa (L.) Tandy is a small red alga, commonly found growing in dense tufts on Ascophyllum. The rhizoids penetrate the host. It is considered by some as parasitic.

Varieties and forms
Several different varieties and forms of this species have been described.
 * Ascophyllum nodosum var. minor has been described from Larne Lough in Northern Ireland.

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 sea lochs in Scotland and Ireland.

The species is found in a range of coastal habitats from sheltered estuaries to moderately exposed coasts, often it dominates the inter-tidal zone (although sub-tidal populations are known to exist in very clear waters). However it is rarely found on exposed shores, and if it is found the fronds are usually small and badly scratched.

It has been recorded as an accidental introduction to San Francisco, California, and eradicated as a potential invasive species there.

Distribution
Recorded in Europe from: Faroes, Norway, Ireland, Britain and Isle of Man Netherlands North America: Bay of Fundy, Nova Scotia, Baffin Island, Hudson Strait, Labrador and Newfoundland.

Uses
Ascophyllum nodosum is harvested for use in alginates, fertilisers and for the manufacture of seaweed meal for animal and human consumption. It has long been used as an organic and mainstream fertilizer for many varieties of crops due to its combination of both macronutrient, (eg. N, P, K, Ca, Mg, S) and micronutrients (eg. Mn, Cu, Fe, Zn, etc.) It also host to cytokinins, auxin-like, gibberellins, betaines, mannitol, organic acids, polysaccharides, amino acids, and proteins which are all very beneficial and widely used in agriculture.

Ascophyllum nodosum along with Macrocystis pyferais harvested in Ireland, Scotland and Norway from which alginates are extracted it is one of the world's principal alginate supply.