BIOTIC Species Information for Himanthalia elongata
Researched byNicola White Data supplied byMarLIN
Refereed byDr Dagmar Stengel
Scientific nameHimanthalia elongata Common nameThongweed
MCS CodeZR389 Recent SynonymsNone

PhylumChromophycota Subphylum
Superclass ClassPhaeophyceae
Subclass OrderFucales
Suborder FamilyHimanthaliaceae
GenusHimanthalia Specieselongata

Additional InformationAlso commonly known as sea thong.
Taxonomy References Stengel et al., 1999,
General Biology
Growth formCapitate / Clubbed
Straplike / Ribbonlike
Feeding methodPhotoautotroph
Mobility/MovementPermanent attachment
Environmental positionEpifloral
Typical food typesNot relevant HabitAttached
BioturbatorNot relevant FlexibilityHigh (>45 degrees)
FragilityIntermediate SizeLarge(>50cm)
Height Growth Ratemax. 16 mm/day
Adult dispersal potentialNone DependencyIndependent
General Biology Additional Information
  • Himanthalia elongata has a two stage morphology. A small button-like frond is first produced, from which large strap-like reproductive fronds are formed. The button stage is clubbed shaped at first and then develops into a button shape 2-3 cm in diameter, which is connected to the substrate by a holdfast and short stipe. Each button typically produces 2 strap-like reproductive fronds in autumn, although plants have been observed with 1 to 4 straps.
  • "Growth rate" refers to growth of reproductive straps at 10-12 degrees C, which is the optimum growing temperature in spring.
  • "Size at maturity" refers to the minimum diameter of the button, which is required for it to produce receptacles.
Biology References Stengel et al., 1999,
Distribution and Habitat
Distribution in Britain & IrelandAll coasts of Britain and Ireland, except south east England.
Global distributionNorway, Britain, Ireland, north west coast of France, northern Spain and Portugal.
Biogeographic rangeNot researched Depth rangeNot relevant
Distribution Additional Information
  • The distribution of Himanthalia elongata appears to be controlled by the degree of wave exposure, presence of tidal currents and the availability of suitable substrata. The species grows best in areas with strong tidal currents and is most commonly found on semi-exposed shores where, it can be locally abundant. It is rarely found in exposed shores and occasionally forms dense stands on sheltered shores.
  • The degree of exposure to waves is also important in determining the persistence of adult plants on the shore. On exposed sites, adult plants may only be present until October, whereas on sheltered sites, plants may be present until February.
  • Zygotes of this species are intolerant of lowered salinity and silt, restricting the species' distribution. Himanthalia elongata is typically found in the lower eulittoral and sometimes extends into the shallow sublittoral. The species can tolerate the physical conditions found further up the shore, but it is prevented from growing there by grazing pressure.
  • Plants from exposed sites tend to be shorter and have fewer, narrower receptacles. Plants grow well in the presence of a red algal turf, which offers protection to young vegetative stages from wave action.

Substratum preferencesBedrock
Large to very large boulders
Physiographic preferencesOpen coast
Strait / sound
Ria / Voe
Biological zoneLower Eulittoral
Sublittoral Fringe
Wave exposureModerately Exposed
Tidal stream strength/Water flowStrong (3-6 kn)
Moderately Strong (1-3 kn)
Weak (<1 kn)
SalinityFull (30-40 psu)
Habitat Preferences Additional Information
Distribution References Stengel et al., 1999, Moss et al., 1973, Hardy & Guiry, 2003,
Reproduction/Life History
Reproductive typeGonochoristic
Developmental mechanismNot relevant
Insufficient information
Spores (sexual / asexual)
See additional information
Reproductive SeasonJune to December Reproductive LocationInsufficient information
Reproductive frequencySemelparous Regeneration potential No
Life span3-5 years Age at reproductive maturity1-2 years
Generation time3-5 years FecundityInsufficient information
Egg/propagule sizeZygotes 0.2 mm across Fertilization typeInsufficient information
Larval/Juvenile dispersal potentialInsufficient information Larval settlement periodInsufficient information
Duration of larval stageInsufficient information   
Reproduction Preferences Additional Information
  • Himanthalia elongata has a life history and growth pattern unique among the Fucales. The species invests 98 percent of the total biomass in reproductive rather than vegetative tissue. It is usually has a biennial lifecycle, reproducing once and then dying.
  • The reproductive bodies or receptacles take the form of long straps, which sprout from the centre of the button. When the plants are fertile the straps become mottled with brown spots, each spot with a pale centre marking the opening to the conceptacle.
  • Gametes are released from June until winter. Usually germlings become visible on the shore in early March and form buttons with an average size of 10-25 mm by August. Those buttons which grow to 15 mm by November produce receptacles that autumn. The receptacles grow little in length during autumn and winter but increase rapidly between February and May. From June onwards, adult plants release gametes on a low tide by liberating them into mucus, which dribbles onto the substratum below. The time of reproduction is strongly site dependent, probably due to water temperature.
  • Zygotes of the species are very large in comparison to most seaweeds. They are spherical, heavy and measure 0.2mm across so that they rapidly settle to the substratum. After fertilisation there is a long period of 5-7 days before attaching rhizoids develop. During this period the zygote is anchored to the substratum using the fertilization membrane, which is expanded into a wide brim. Zygotes are incapable of growing on silt, but germlings are tolerant of temporary cover by drifting sand.
  • Gamete dispersal is thought to be limited so recruitment from external populations is probably low. Early germling growth is probably strongly influenced by the presence of adults, as reproductive thalli provide protection from desiccation and high irradiances, although shading could limit growth rate of germlings (Stengel, pers. comm.).
Reproduction References Stengel et al., 1999, Moss et al., 1973,
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