BIOTIC Species Information for Alaria esculenta
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Researched byDr Harvey Tyler-Walters Data supplied byMarLIN
Refereed byDr Stefan Kraan
Scientific nameAlaria esculenta Common nameDabberlocks
MCS CodeZR341 Recent SynonymsAlaria platyrhiza

PhylumChromophycota Subphylum
Superclass ClassPhaeophyceae
Subclass OrderLaminariales
Suborder FamilyAlariaceae
GenusAlaria Speciesesculenta

Additional InformationOther common names include wing kelp, honeyware, edible fucus, and bladder locks in England; dabberlocks and keys in Scotland; and murlins, ribini, and Cupog nag Cloc in Ireland (Guiry 2000). The species name Alaria esculenta literally means 'edible wings'. This species was originally described as Fucus esculentus Linnaeus, 1767. The class Phaeophyceae may alternatively be classified in the Phylum Heterokontophyta ( Hoek van den et al. 1995).

Alaria (Phaeophyceae, Alariaceae) is a common genus of kelps in the northern hemisphere. Fourteen species are currently recognised of which three (Alaria esculenta (L.) Greville, Alaria pylaii (Bory de Saint-Vincent) Greville, and Alaria grandifolia J. Agardh) are reported for the cold -temperate North Atlantic Ocean. Alaria esculenta, the type species described originally from the North Atlantic, exhibits a range of biogeographically correlated morphotypes suggesting the possibility of multiple specific or intraspecific entities or hybrids (Kraan pers. comm.; Kraan & Guiry 2000 in press). A key to the species of the genus Alaria is given by Widdowson (1971).

Taxonomy References Hiscock, 1979, Hayward et al., 1996, Birkett et al., 1998b, Lüning, 1990, Guiry, 2000, Kraan & Guiry, 2000, Hoek van den et al., 1995, Widdowson, 1971,
General Biology
Growth formStraplike / Ribbonlike
Feeding methodPhotoautotroph
Mobility/MovementPermanent attachment
Environmental positionEpifloral
Typical food typesNot relevant HabitAttached
BioturbatorNot relevant FlexibilityHigh (>45 degrees)
FragilityRobust SizeLarge(>50cm)
Height Growth Rate20 cm/month
Adult dispersal potentialNone DependencyIndependent
General Biology Additional Information
  • Alaria esculenta forms the main canopy in exposed rocky areas.
  • Alaria esculenta is a colonizing species that will occur in recently denuded rock surfaces in exposed to sheltered situations.
  • Maximum growth rates in the field (20 cm/month) occur in April and May (Isle of Man). Plants on adjacent rope aquaculture system had an average growth rate of 5 cm per day (Birkett et al., 1999b). Kain & Dawes (1987) reported growth rates of 10 cm per day during one spring growth period on a rope aquaculture system in the Isle of Man. However, fields trials with different strains of Alaria esculenta resulted in highest growth rates of 25 cm/month and lowest rates of 5 cm/month (Kraan pers. comm.).
  • In June and July growth slows and the blade becomes eroded and damaged by wave action depending on depth. Alaria esculenta in the lower eulittoral and upper sublittoral will erode away completely due to higher summer water temperatures and bleaching by sunlight. Populations at 2 m or more below low water survive (Kraan pers. comm.).
  • In strong currents and low wave action the blade may reach 4 m in length (e.g. Aran Islands, Ireland; Guiry, 1997).
  • A short stipe and narrow lamina base is characteristic of exposed conditions whereas in sheltered conditions the stipe is long and the lamina base wider (Widdowson, 1971).
Biology References Birkett et al., 1998b, Lüning, 1990, Connor et al., 1997(a), Lobban & Harrison, 1997, Dring, 1982, Hoek van den et al., 1995, Guiry, 1997, Widdowson, 1971, Kain & Dawes, 1987,
Distribution and Habitat
Distribution in Britain & IrelandFound around the Shetland Isles, Orkney and east coast of Scotland, south to Flamborough Head in England. Its distribution continues along the south west of England and the west coasts of England, Wales, Scotland and Ireland including the Isle of Man.
Global distributionAlaria esculenta occurs in the North Atlantic from Novaya Zemlya to Iceland and south to Brittany in the east and from the shores of Greenland to the Bering Strait in the west. It also occurs in the Bering Sea and Sea of Japan in the North Pacific
Biogeographic rangeNot researched Depth range0-8 m
MigratoryNon-migratory / Resident   
Distribution Additional InformationAlaria esculenta is absent from most of the east coast of England, primarily due to a lack of suitable substrata. The species is found all around the Irish coast, where rocky shores as substratum are available. It occurs at a depth of 15 m in the Aran Islands and below 35 m off the Scellig Islands, Ireland and Rockall.

Alaria esculenta is present in the North Pacific and North Atlantic, where it is located north as far as the winter sea ice and as far south as the 16 °C summer isotherm, represented by the French coast of Brittany in the European North Atlantic (Luning, 1990). Its absence in the southern North Sea and English Channel is due to high summer surface temperatures of 16 °C, which it cannot survive (Munda & Luning, 1977; Widdowson, 1971; Sundene, 1962). Its distribution in the Arctic Sea is associated with the -2 °C February winter isotherm (Kraan pers. comm.).

Substratum preferencesBedrock
Large to very large boulders
Small boulders
Artificial (e.g. metal/wood/concrete)
Physiographic preferencesOpen coast
Biological zoneLower Eulittoral
Upper Infralittoral
Sublittoral Fringe
Wave exposureExtremely Exposed
Very 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 Fish & Fish, 1996, Hayward et al., 1996, Birkett et al., 1998b, Lüning, 1990, Guiry, 2000, Sundene, 1962, Dring, 1982, JNCC, 1999, Picton & Costello, 1998, Kraan & Guiry, 2000, Munda & Luning, 1977, Newton, 1931, Hardy & Guiry, 2003,
Reproduction/Life History
Reproductive typeAlternation of generations
Developmental mechanismSpores (sexual / asexual)
Reproductive SeasonInsufficient information Reproductive LocationWater column
Reproductive frequencyAnnual episodic Regeneration potential No
Life span3-5 years Age at reproductive maturity<1 year
Generation time1 year Fecundity>1,000,000
Egg/propagule size Fertilization typeExternal
Larval/Juvenile dispersal potential10-100m Larval settlement period
Duration of larval stage1 day   
Reproduction Preferences Additional InformationThe fecundity reported above is for zoospore production. Both the sporophyte and gametophyte are photoautotrophs but only the gametophyte may develop vegetatively.
  • Dispersal potential varies with phase in the life cycle; zoospores may disperse <2m whereas gametophytes may disperse between 1 -10 m by drifting, maybe up to 100 m (Kraan pers. comm.).
  • Alaria esculenta is a perennial and lives for 4 -5 years in the Irish Sea and up to 7 years in Norway.
  • Two rows of ligulate sporophylls form in the upper parts of the stipe during spring and in a lesser amount in autumn only (Kraan pers. comm.; Widdowson, 1971).
  • New sporophytes appear in early spring and zoospores are produced from sporophylls between October and May (Kraan pers. comm.; Birkett et al., 1998b).
  • The sporophylls produce haploid spores (zoospores), by meiosis, that germinate to form the haploid or gametophytic phase (male and female). Gametophytes produce the gametes (sperm and eggs) which fuse after fertilization to form a zygote. The zygotes germinates to form diploid platelets (germlings), the sporophytic phase. Thus the life history is that the large seaweed (sporophyte) alternates with a microscopic filamentous phase (Hoek van den, 1995). Therefore, Alaria esculenta is dioecious and has a heteromorphic diplohaplontic life history.
  • The flagellated zoospores are about 5 microns in diameter. They loose their flagella after 24 hrs and settle on the available substrata (Birkett et al., 1998b). However, settling rate is dependant on the local currents, therefore spore settling time is probably longer than 1 day.
  • Sundene (1961) noted that next generation sporophytes developed within 10 m of the parent plants in Drobak, Norway. Norton (1992) suggested that the position of the sporophylls close to the substratum may limit dispersal potential, however the local currents are probably of overriding importance for dispersal.
  • Gametophytes become fertile in under 10 days in optimal conditions.
  • Successful fertilization requires a high density of spore settlement (about 1 mm apart).
  • Maturation of the gametophytes can be delayed under less optimal conditions, for example, low light, and 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.
  • Spore production may be inhibited by epifauna such as Membranipora membranacea (sea mat) and endophytes such as Streblonema sp.
Reproduction References Birkett et al., 1998b, Lüning, 1990, Lobban & Harrison, 1997, Stein et al., 1995, Guiry & Blunden, 1991, Sundene, 1962, Dring, 1982, Lein et al., 1991, Norton, 1992, Kain & Dawes, 1987,
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