Zostera marina

Researched ByDr Harvey Tyler-WaltersData Supplied ByMarLIN
Refereed byDr Leigh Jones
Taxonomy
Scientific nameZostera marinaCommon nameCommon eelgrass
MCS CodeNoneRecent SynonymsNone
PhylumAnthophytaSubphylum
SuperclassClassLiliopsida
SubclassOrderPotamogetonales
SuborderFamilyZosteraceae
GenusZosteraSpeciesmarina
Subspecies  
Additional InformationOther common names include, wigeon grass, broad leaved grass wrack, marlee, sedge and slitch. Perennial populations show a seasonal changes in leaf growth, the long leaves found in summer are replaced by shorter, slow growing leaves in winter. The morphological characteristics, especially leaf width may vary with environmental conditions (Phillips & Menez 1988). In the UK literature Zostera marina is distinguished from Zostera angustifolia on the basis of morphology. However, outside the UK most authors consider Zostera angustifolia to be a phenotypic variant of Zostera marina. To avoid confusion only data relating to Zostera marina is presented.
Taxonomy References Hartog den, 1970, Phillips & Menez, 1988, Davison & Hughes, 1998, Guiry, 2000, NBN, 2002
General Biology
Growth formFolioseFeeding methodPhotoautotroph
Mobility/MovementPermanent attachmentEnvironmental positionEpifloral, Infaunal
Typical food typesNot relevantHabitAttached
BioturbatorNot relevantFlexibilityHigh (>45 degrees)
FragilityIntermediateSizeMedium-large(21-50cm)
HeightExceptionally, up to 2 mGrowth Rate5 m/year
Adult dispersal potential10-100mDependencyIndependent
SociabilitySolitary
Toxic/Poisonous?No
Additional InformationThe stated growth rate refers to vegetative growth recorded in perennial populations whereas annual populations may expand at 30m / year in good conditions (Holt et al. 1997). The following species have been recorded only from seagrass leaves:
  • the hydroid Laomedea angulata;
  • the algae Rhodophysema georgii, Halothrix lumbricalis,Leblondiella densa, Myrionema magnusii, Cladosiphon zosterae, Punctaria crispata; and
  • Cladosiphon contortus, which is larger and found primarily on Zosterasp.
    • rhizomes.
Biology References Hartog den, 1970, Phillips & Menez, 1988, Davison & Hughes, 1998, Jones et al., 2000, Anonymous, 1999(p), Holt et al., 1997
Distribution and Habitat
Distribution in Britain & IrelandZostera marina has a wide but patchy distribution in southwest of England, the Solent and Isle of Wight on the south coast, Wales, western Ireland, western and eastern Scotland including Orkney and the Shetland Islands.
Global distributionWidespread through the Atlantic and Pacific. It is the only seagrass species that extends into the Arctic Circle. It has a restricted distribution in the Mediterranean.
Biogeographic rangeNot researchedDepth range0 to 5m
MigratoryNon-migratory / Resident
Distribution Additional InformationIn 1920s and 1930s the previously extensive beds of eelgrass were severely reduced by an outbreak of 'wasting disease', which appears to affect sublittoral Zostera marina primarily. To date, recovery has been poor or slow. An exceptional bed of Zostera marina occurs in the clear waters of Ventry Bay, south-west Ireland and extends from 0.5 to 10m in depth and up to 13m deep in some patches. It should be noted that the global distribution of Zostera marina includes records of Zostera angustifolia which is considered synonymous outside the UK. It extends from Arctic Circle in northern Russia to near Gibraltar, Spain along the European coast. In has a restricted distribution in the Mediterranean, limited to northern parts of Adriatic and Aegean Seas, brackish etangs and lagoons in southern France. On the western Atlantic coast it extends from west coast of Alaska to North Carolina. In the Pacific it is recorded from Japan, Korea and from Alaska to Baja California, Mexico.
Substratum preferencesGravel / shingle, Muddy gravel, Sandy mud, Muddy sandPhysiographic preferencesEstuary, Isolated saline water (Lagoon), Enclosed coast / Embayment
Biological zoneSublittoral Fringe, Upper InfralittoralWave exposureSheltered, Very Sheltered
Tidal stream strength/Water flowWeak (<1 kn), Very Weak (negligible)SalinityVariable (18-40 psu)
Habitat Additional Information
Distribution References Hartog den, 1970, Phillips & Menez, 1988, Davison & Hughes, 1998, Jones et al., 2000, Stewart et al., 1994, NBN, 2002
Reproduction/Life History
Reproductive typeVegetative, Protogynous hermaphrodite Developmental mechanismOviparous
Reproductive SeasonMay to SeptemberReproductive Location
Reproductive frequencyAnnual episodic Regeneration potentialNo
Life span21-50 yearsAge at reproductive maturity1-2 years
Generation time1-2 yearsFecundityInsufficient information
Egg/propagule sizeFertilization type
Larvae/Juveniles
Larval/Juvenile dispersal potential100-1000mLarval settlement periodNot relevant
Duration of larval stageNot relevant  
Additional InformationZostera sp. are perennials but may act as annuals under stressful conditions (Phillips & Menez 1988). Eelgrass reproduces vegetatively, i.e.. by growth of rhizome. Vegetative reproduction probably exceeds seedling recruitment except in areas of sediment disturbance (Reusch et al. 1998; Phillips & Menez 1988). Examination of the population structure of a Zostera marina bed in the Baltic Sea suggested that individual genotypes (vegetatively produced clones) may be up to 50 years old and further suggested that the eelgrass bed at that site had been present for at least 67 years (Reusch et al. 1998).
    Methods of dispersal:
  • All parts of the plant may float if they become detached from substrate. Pieces of rhizome or shoots (if displaced by for example storm action) may take root if they settle on suitable substratum.
  • The generative stalk may be released together with the seed compliment and may be carried great distances (Phillips & Menez, 1988).
  • In New York, USA, Churchill et al. (1985) recorded 5-13 percent of seeds with attached gas bubbles and achieved an average dispersal distance of 21m and up to 200m in a few cases.
  • Wildfowl may disperse seeds on their feet, or in their gut.. For example, 30 percent of freshwater eelgrass (Naja marina) seeds fed to ducks in Japan survived and successfully germinated after passage through their alimentary canals and potentially transported 100-200km (Fishman & Orth 1996).
Phillips & Menez (1988) state that seedling mortality is extremely high. Fishman & Orth (1996) report that 96 percent of seeds were lost from uncaged test areas due to transport (dispersal) or predation. Ecological genetics studies of Zostera marina in False and Padilla Bays on Pacific coast of USA (Ruckelhaus 1998), detected genetic differentiation between intertidal and subtidal zones and between the bays. Estimates of gene flow suggested that seed dispersal was more important than pollen dispersal, effective migration (2.9 migrants/generation) occurred between the bays (14 km apart) and that the population subdivision was in part explained by disturbance and recolonization. Phillips & Menez (1988) note that seedlings rarely occur within the eelgrass bed except in areas cleared by storms, blow-out or excessive herbivory.
Reproduction References Hartog den, 1970, Phillips & Menez, 1988, Davison & Hughes, 1998, Reusch et al., 1998, Churchill et al., 1985, Stewart et al., 1994, Fishman & Orth, 1996, Rucklehaus, 1998