BIOTIC Species Information for Ascophyllum nodosum
Researched byJacqueline Hill & Nicola White Data supplied byMarLIN
Refereed byDr Dagmar Stengel
Scientific nameAscophyllum nodosum Common nameKnotted wrack
MCS CodeZR375 Recent SynonymsNone

PhylumChromophycota Subphylum
Superclass ClassPhaeophyceae
Subclass OrderFucales
Suborder FamilyFucaceae
GenusAscophyllum Speciesnodosum

Additional InformationDetached forms of Ascophyllum nodosum are known from several habitats. Ascophyllum nodosum var. mackaii is found on very sheltered shores, in sea lochs and is sometimes common on the west coasts of Ireland and Scotland. The frond has extensive dichotomous branching and bears few air bladders. The plants drift in large, spherical masses in sheltered waters. Ascophyllum nodosum var. scorpioides, which is abundant in New Hampshire (U.S.A.), is often associated with the marsh grass Spartina alterniflora. According to Gibb (1957) the major difference between the ecads mackaii and scorpioides is the proportion of apical to lateral branching. If branching is both 'apical and lateral' the algae would be designated as mackaii while if it is 'almost entirely lateral' it would be designated as scorpioides. Unattached forms arise when detached fragments of Ascophyllum nodosum are deposited onto the shore where they continue to multiply and branch independently of the original fragment (Chock & Mathieson, 1976).

Chock & Mathieson (1979) demonstrated the physiological responses of Ascophyllum nodosum and its detached ecad scorpioides were similar under varying conditions of light intensity, temperature and salinity.

Ascophyllum nodosum var. mackaii:
The presence of the ecad in any particular situation depends on the combination of a number of conditions applying at a tide level between high and low water neaps:
  • frequent alternation of high and low salinities so a supply of freshwater is of primary importance;
  • good shelter from wave action because of the unattached state of the ecad;
  • absence of fast moving water, whether caused by freshwater streams or tidal conditions;
  • flat, undulating or slightly sloping shore profile where stability is high, and
  • substratum type, the porosity of which affects the conditions of salinity and also influences, to some extent, the development of the ecad.
Very sheltered conditions are often found at loch heads on the west coast of Scotland and in these situations the ecad is sometimes present in great abundance. Sheltered or land-locked bays or situations in the lee of small islands are other favourable positions (Gibb, 1957).
Taxonomy References Chock & Mathieson, 1979, Chock & Mathieson, 1976, Gibb, 1957,
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