Himanthalia elongata

Researched By	Nicola White	Data Supplied By	MarLIN
Refereed by	Dr Dagmar Stengel
Taxonomy
Scientific name	Himanthalia elongata	Common name	Thongweed
MCS Code	ZR389	Recent Synonyms	None
Phylum	Chromophycota	Subphylum
Superclass		Class	Phaeophyceae
Subclass		Order	Fucales
Suborder		Family	Himanthaliaceae
Genus	Himanthalia	Species	elongata
Subspecies
Additional Information	Also commonly known as sea thong.
Taxonomy References	Stengel et al., 1999
General Biology
Growth form	Capitate / Clubbed, Straplike / Ribbonlike	Feeding method	Photoautotroph
Mobility/Movement	Permanent attachment	Environmental position	Epifloral, Epilithic
Typical food types	Not relevant	Habit	Attached
Bioturbator	Not relevant	Flexibility	High (>45 degrees)
Fragility	Intermediate	Size	Large(>50cm)
Height		Growth Rate	max. 16 mm/day
Adult dispersal potential	None	Dependency	Independent
Sociability	Solitary
Toxic/Poisonous?	No
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 & Ireland	All coasts of Britain and Ireland, except south east England.
Global distribution	Norway, Britain, Ireland, north west coast of France, northern Spain and Portugal.
Biogeographic range	Not researched	Depth range	Not relevant
Migratory
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 preferences	Bedrock, Large to very large boulders	Physiographic preferences	Open coast, Strait / sound, Sealoch, Ria / Voe
Biological zone	Lower Eulittoral, Sublittoral Fringe	Wave exposure	Moderately Exposed, Sheltered
Tidal stream strength/Water flow	Strong (3-6 kn), Moderately Strong (1-3 kn), Weak (<1 kn)	Salinity	Full (30-40 psu)
Habitat Additional Information
Distribution References	Stengel et al., 1999, Moss et al., 1973, Hardy & Guiry, 2003
Reproduction/Life History
Reproductive type	Gonochoristic	Developmental mechanism	Not relevant, Ovoviviparous, Insufficient information, Spores (sexual / asexual), Oviparous, See additional information
Reproductive Season	June to December	Reproductive Location	Insufficient information
Reproductive frequency	Semelparous	Regeneration potential	No
Life span	3-5 years	Age at reproductive maturity	1-2 years
Generation time	3-5 years	Fecundity	Insufficient information
Egg/propagule size	Zygotes 0.2 mm across	Fertilization type	Insufficient information
Larvae/Juveniles Larval/Juvenile dispersal potential Insufficient information Larval settlement period Insufficient information Duration of larval stage Insufficient information
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