Laminaria digitata

Researched By	Jacqueline Hill	Data Supplied By	MarLIN
Refereed by	This information is not refereed.
Taxonomy
Scientific name	Laminaria digitata	Common name	Oarweed
MCS Code	ZR350	Recent Synonyms	Laminaria cucullata f. longipes, Laminaria cucullata f. apoda.
Phylum	Chromophycota	Subphylum
Superclass		Class	Phaeophyceae
Subclass		Order	Laminariales
Suborder		Family	Laminariaceae
Genus	Laminaria	Species	digitata
Subspecies
Additional Information	Common 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 form	Digitate, Foliose, Straplike / Ribbonlike	Feeding method	Photoautotroph
Mobility/Movement	Permanent attachment	Environmental position	Epilithic, Epifloral
Typical food types	Not relevant	Habit	Attached
Bioturbator	Not relevant	Flexibility	High (>45 degrees)
Fragility	Robust	Size	Large(>50cm)
Height	Up to 2 m	Growth Rate	1.3 cm/day
Adult dispersal potential	None	Dependency	Independent
Sociability	Solitary
Toxic/Poisonous?	No
Additional Information	Kelps 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 & Ireland	Most 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 distribution	Recorded 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 range	Not researched	Depth range	Lower intertidal to 20 m
Migratory	Non-migratory / Resident
Distribution Additional Information	There 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 preferences	Bedrock, Large to very large boulders, Small boulders, Cobbles, Pebbles, Artificial (e.g. metal/wood/concrete)	Physiographic preferences	Open coast, Strait / sound, Ria / Voe, Enclosed coast / Embayment
Biological zone	Sublittoral Fringe, Lower Eulittoral, Upper Infralittoral	Wave exposure	Very Exposed, Exposed, Moderately Exposed, Sheltered
Tidal stream strength/Water flow	Very Strong (>6 kn), Strong (3-6 kn), Moderately Strong (1-3 kn), Weak (<1 kn)	Salinity	Full (30-40 psu)
Habitat 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 type	Gonochoristic, Alternation of generations, Oogamous	Developmental mechanism	Spores (sexual / asexual)
Reproductive Season	All year	Reproductive Location
Reproductive frequency	Annual protracted	Regeneration potential	No
Life span	6-10 years	Age at reproductive maturity	1-2 years
Generation time	1-2 years	Fecundity	In excess of 1,000,000
Egg/propagule size	Zoospores ca 5µm across	Fertilization type	External
Larvae/Juveniles Larval/Juvenile dispersal potential 100-1000m Larval settlement period All year (see additional information) Duration of larval stage 1 day
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