BIOTIC Species Information for Laminaria digitata
Researched byJacqueline Hill Data supplied byMarLIN
Refereed byThis information is not refereed.
Scientific nameLaminaria digitata Common nameOarweed
MCS CodeZR350 Recent SynonymsLaminaria cucullata f. longipes, Laminaria cucullata f. apoda.

PhylumChromophycota Subphylum
Superclass ClassPhaeophyceae
Subclass OrderLaminariales
Suborder FamilyLaminariaceae
GenusLaminaria Speciesdigitata

Additional InformationCommon names in England also include Tangle, Red ware and Sea girdle. In Ireland common names include Leath and Learach. The length of the frond varies with season, age of plant and location, reaching over 1 m in suitable conditions. The number of frond digits vary with amount of exposure. In shelter these are few and short, but with increasing exposure, they are more numerous (up to 10 or 12) and extend almost to the base of the frond. Reported to store sodium glutamate and thus tasty when dried.
Taxonomy References Howson & Picton, 1997, Dickinson, 1963, Hayward et al., 1996, Guiry, 2000, Guiry, 2006,
General Biology
Growth formDigitate
Straplike / Ribbonlike
Feeding methodPhotoautotroph
Mobility/MovementPermanent attachment
Environmental positionEpilithic
Typical food typesNot relevant HabitAttached
BioturbatorNot relevant FlexibilityHigh (>45 degrees)
FragilityRobust SizeLarge(>50cm)
HeightUp to 2 m Growth Rate1.3 cm/day
Adult dispersal potentialNone DependencyIndependent
General Biology Additional InformationKelps of the family Laminariaceae exhibit an alternation of generations, which involves dissimilar (heteromorphic) phases; an asexual diploid phase (the sporophyte) is usually of considerable size and a haploid dioecious phase (the gametophyte) that is microscopic. Sporophytes of Laminaria digitata can grow to a length of 2-4m. Growth rate is seasonally controlled with a period of rapid growth from February to July and one of slower growth from August to January. The growth rate given is the mean growth rate during season of maximal growth (Kain 1979). There is no defined growth zone in Laminaria digitata but growth is diffuse in the lamina (blade). In general the whole new lamina is able to grow but throughout the year it is greatest near the base.
Biology References Dickinson, 1963, Guiry & Blunden, 1991, Birkett et al., 1998b, Kain, 1979, Bolten & Lüning, 1982,
Distribution and Habitat
Distribution in Britain & IrelandMost coasts of Britain and Ireland, including Rockall. Scarce along east coast of England, particularly between Ouse and Thames estuaries, due to turbidity and lack of hard substrata. Absent from Liverpool Bay and Severn estuary due to turbidity.
Global distributionRecorded from the Atlantic coasts of Europe as far north as Novaya Zemlya and south to the Canary Islands, including Iceland. Also found in southern Greenland and east coast Canada, Quebec and North America from Hudson Straits to New York.
Biogeographic rangeNot researched Depth rangeLower intertidal to 20 m
MigratoryNon-migratory / Resident   
Distribution Additional InformationThere is a marked difference in the lower depth limit of Laminaria digitata between the various parts of its geographical range. Depth is determined by water clarity and competition. In the Isle of Man the lower limit is at 1-2m below the lowest astronomical tide and at Milford Haven it has been recorded at 5m. In the north of its range Laminaria digitata extends to depths of 15-20m (Birkett et al., 1998b). Where %Laminaria hyperborea% thrives it out-competes Laminaria digitata limiting the lower limit of Laminaria digitata (Kain 1975).
The salinity optimum for Laminaria digitata is full salinity. However, on the Norwegian coast, subject to seasonal fluctuations in salinity, Sundene (1964) found healthy Laminaria digitata plants growing between 15 and 25psu.

Substratum preferencesBedrock
Large to very large boulders
Small boulders
Artificial (e.g. metal/wood/concrete)
Physiographic preferencesOpen coast
Strait / sound
Ria / Voe
Enclosed coast / Embayment
Biological zoneSublittoral Fringe
Lower Eulittoral
Upper Infralittoral
Wave exposureVery Exposed
Moderately Exposed
Tidal stream strength/Water flowVery Strong (>6 kn)
Strong (3-6 kn)
Moderately Strong (1-3 kn)
Weak (<1 kn)
SalinityFull (30-40 psu)
Habitat Preferences Additional Information
Distribution References Guiry & Blunden, 1991, Birkett et al., 1998b, Kain, 1979, Kain, 1975, Bolten & Lüning, 1982, Sundene, 1964, Bassindale et al., 1948, Hardy & Guiry, 2003, Guiry, 2006,
Reproduction/Life History
Reproductive typeGonochoristic
Alternation of generations
Developmental mechanismSpores (sexual / asexual)
Reproductive SeasonAll year Reproductive Location
Reproductive frequencyAnnual protracted Regeneration potential No
Life span6-10 years Age at reproductive maturity1-2 years
Generation time1-2 years FecundityIn excess of 1,000,000
Egg/propagule sizeZoospores ca 5µm across Fertilization typeExternal
Larval/Juvenile dispersal potential100-1000m Larval settlement periodAll year (see additional information)
Duration of larval stage1 day   
Reproduction Preferences Additional Information
  • Laminaria digitata is a perennial and lives for 4 to 6 years (Birkett et al., 1998b).
  • Laminarians exhibit alternation of generations with morphologically dissimilar (heteromorphic) reproductive phases. An asexual diploid phase (the sporophyte) is usually of considerable size and a haploid dioecious phase (the gametophyte) is microscopic.
  • The sporophyte produces vast numbers of haploid zoospores from sporangia which develop in small patches called sori on the lamina.
  • The flagellated zoospores are about 5 microns in diameter and may be transported at least 200 m from the parent (Birkett et al., 1998b). They loose their flagella after 24 hrs and settle on any available substrata.
  • The zoospores develop into microscopic dioecious haploid gametophytes, male plants producing spermatozoid and female plants developing oogonia. The gametophytes become fertile in under 10 days in optimal conditions: low temperatures and blue light.
  • Maturation of the gametophytes can be delayed under less optimal conditions, for example in red light development remains vegetative. Fragments of damaged vegetative gametophytes may develop into separate gametophytes (only a few cells are required) hence reproductive potential may be increased. If optimal conditions return the gametophyte may become fertile and produce gametes (Hoek van den et al., 1995).
  • Male and female gametes must settle at a high density (within 1mm of each other) if the maturing gametangial egg is to be fertilized. On fertilization of the extruded egg, young sporophytes start to grow in-situ.
  • Sori are produced over most of the blade surface (except most distal or proximal areas) all year round with maxima in July - August and November - December.
  • Young sporophytes (germlings) appear all year with maxima in spring and autumn.
  • Chapman (1981) demonstrated that substantial recruitment of Laminaria digitata plants to areas barren of kelp plants was possible up to 600m away from reproductive plants.
Reproduction References Birkett et al., 1998b, Kain, 1979, Chapman, 1981, Hoek van den et al. 1995,
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