BIOTIC Species Information for Fucus distichus
Researched byNicola White Data supplied byMarLIN
Refereed byDr Graham Scott
Scientific nameFucus distichus Common nameA brown seaweed
MCS CodeZR380 Recent SynonymsFucus distichus distichus, Powell, 1957a; Fucus distichus anceps, Powell, 1957a.

PhylumChromophycota Subphylum
Superclass ClassPhaeophyceae
Subclass OrderFucales
Suborder FamilyFucaceae
GenusFucus Speciesdistichus

Additional InformationNo text entered
Taxonomy References Rice & Chapman, 1985, Fish & Fish, 1996, Howson & Picton, 1997,
General Biology
Growth formFoliose
Feeding methodPhotoautotroph
Mobility/MovementPermanent attachment
Environmental positionEpifloral
Typical food typesNot relevant HabitAttached
BioturbatorNot relevant FlexibilityHigh (>45 degrees)
FragilityIntermediate SizeMedium-large(21-50cm)
HeightUp to 30 cm Growth Rate10 cm / year
Adult dispersal potentialNot researched DependencyIndependent
General Biology Additional InformationThe morphology of Fucus distichus is remarkably varied. Powell (1957a) recognised four subspecies, which were later separated into two distinct species (Fucus distichus and Fucus evanescens) by Rice and Chapman (1985). In its rock pool habit on the east coast of North America Fucus distichus is considered by Pearson & Davison (1994) to be slow growing, a poor competitor and stress intolerant. Adults of Fucus distichus are very tolerant of grazing due to a high content of phlorotannin, but germlings do not have any protection and are susceptible to grazing by littorinids.
Biology References Rice & Chapman, 1985, Powell, 1957, Pearson & Davison, 1994, Ang, 1991,
Distribution and Habitat
Distribution in Britain & IrelandRestricted to northern shores of Scotland and north and west Ireland.
Global distributionNorway, northern Scotland, Iceland, Greenland, eastern North America from Labrador to Maine and the Pacific coast of America discontinuously from Alaska to California
Biogeographic rangeNot researched Depth rangeUpper eulittoral
MigratoryNon-migratory / Resident   
Distribution Additional InformationIn Britain and Ireland, Fucus distichus has only been recorded attached to bedrock in the mid to upper eulittoral zone on exposed rocky shores in northern Scotland and Ireland. It is thought to be prevented from growing further south due to its poor tolerance of desiccation and inability to compete with plants growing further down the shore. However, on the east coast of North America, Fucus distichus is only found in rock pools and is incapable of growing on emergent rock surfaces in the mid to upper eulittoral.

Substratum preferencesBedrock
Large to very large boulders
Physiographic preferencesOpen coast
Biological zoneUpper Eulittoral
Wave exposureExtremely Exposed
Very Exposed
Tidal stream strength/Water flowStrong (3-6 kn)
Moderately Strong (1-3 kn)
Weak (<1 kn)
Very Weak (negligible)
SalinityFull (30-40 psu)
Variable (18-40 psu)
Habitat Preferences Additional Information
Distribution References Rice & Chapman, 1985, Ang, 1991, JNCC, 1999, Norton, 1985, Hardy & Guiry, 2003,
Reproduction/Life History
Reproductive typePermanent hermaphrodite
Developmental mechanismNot relevant
Reproductive SeasonApril to August Reproductive LocationInsufficient information
Reproductive frequencyAnnual protracted Regeneration potential No
Life span3-5 years Age at reproductive maturity1-2 years
Generation time1-2 years FecundityInsufficient information
Egg/propagule sizeInsufficient information Fertilization typeInsufficient information
Larval/Juvenile dispersal potentialInsufficient information Larval settlement periodNot relevant
Duration of larval stageInsufficient information   
Reproduction Preferences Additional Information
  • Receptacles of Fucus distichus are initiated in December, they become ripe in April and gametes are released from April to August. Plants usually become mature when 100mm long. The whole plant dies back after reproducing and is removed from the rock by wave action during its third winter. Most plants live for 2 to 3 years (Powell, 1957b).
  • Fucus distichus produces gametes of both sexes within each conceptacle. When released, ova can survive and disperse for several days. Antherozoids can only live for several hours. Self-fertilisation is thought to be high in the species and once a zygote is formed it can only be dispersed over limited distances (Rice et al., 1985).
Reproduction References Powell, 1957(b), Rice et al., 1985, Ang, 1991,
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