Zostera noltii

Researched ByDr Harvey Tyler-WaltersData Supplied ByMarLIN
Refereed byDr Leigh Jones
Taxonomy
Scientific nameZostera noltiiCommon nameDwarf eelgrass
MCS CodeNoneRecent SynonymsZostera nana (Roth)
PhylumAnthophytaSubphylum
SuperclassClassLiliopsida
SubclassOrderPotamogetonales
SuborderFamilyZosteraceae
GenusZosteraSpeciesnoltii
Subspecies  
Additional InformationLike most of Zostera sp. this species may exhibit morphological variation depending on location, tidal zone and age of plant (Phillips & Menez, 1988).
Taxonomy References Phillips & Menez, 1988, Davison & Hughes, 1998, Hartog den, 1970, Anonymous, 1999(p), NBN, 2002
General Biology
Growth formFolioseFeeding methodPhotoautotroph
Mobility/MovementPermanent attachmentEnvironmental positionInfaunal, Epifloral
Typical food typesNot relevantHabitAttached
BioturbatorNot relevantFlexibilityHigh (>45 degrees)
FragilityIntermediateSizeMedium-large(21-50cm)
HeightGrowth RateSee additional text
Adult dispersal potential10-100mDependencyIndependent
SociabilitySolitary
Toxic/Poisonous?No
Additional InformationGrowth
Growth in seagrasses is generally limited by light and affected by temperature (Philliparts, 1995a & b; Marta et al., 1996). Zostera noltii is more tolerant of high light intensities, available at low tide, than Zostera marina, presumably an adaptation to life higher on the shore and the more turbid environment of intertidal flats (Vermaat et al., 1996; Davison & Hughes, 1998). New leaves appear in spring and eelgrass meadows develop over intertidal flats in summer, due to vegetative growth. Increase in shoot density resulting from continuous branching of the rhizome (Vermaat & Verhagen, 1996). A shoot density of 1000-23000 /m² was reported in the Zandkreek estuary, Netherlands (Vermaat & Verhagen, 1996). Leaf growth stops in September/October and leaves are shed although Zostera noltii keeps its leaves longer than Zostera marina in winter. In the intertidal the combined action of grazing and wave action causes leaves to be lost over winter, and the plant reduced to its rhizomes within the sediment. For example, Nacken & Reise (2000) reported that 50% of leaves fell off while the rest were taken by birds (see importance) in the Wadden Sea. In the following season, regrowth occurs from the remaining rhizomes.

The rhizome of Zostera noltii is thinner than that of the longer lived Zostera marina and its growth is rapid and ephemeral in nature, taking advantage of seasonal increases in light and nutrients rather than metabolites stored in the rhizome (Marta et al., 1996; Dawes & Guiry, 1992). Marta et al. (1996) reported shoot growth rates of ca.0.2 cm/day (winter minimum) to ca. 0.8-0.9 cm/day (summer maximum) in the Mediterranean (with winter temperature of 12 °C and summer maximum temperature of 23.2 °C). They also stated that the rhizomes were short lived, <1 year, presumably from one growing season to the next, however given the 'life-span' of vegetative clones of Zostera marina, the plants and seagrass bed of Zostera noltii may be much older.

Epiphytes
The following algal species have been recorded only from seagrass leaves: Halothrix lumbricalis; Leblondiella densa; Myrionema magnusii; Cladosiphon zosterae; Punctaria crispata and Cladosiphon contortus, which is larger and found primarily on Zostera sp. rhizomes. Other species of algae are host specific for Zostera marina. The parasitic fungus Plasmodiophora bicaudata Feldm. prevented growth form rhizome internodes and gives the diseased plant a tufted appearance (den Hartog, 1970).

Productivity
Plus et al. (2001) reported the gross production rates of Zostera noltii beds in the Thau lagoon, France, to be between 97.5 - 1001.3 mg oxygen / m² / h which was within the range reported for other temperate seagrass beds.

Biology References Phillips & Menez, 1988, Davison & Hughes, 1998, Hartog den, 1970, Vermaat et al., 1996, Marta et al., 1996, Nacken & Reise, 2000, Dawes & Guiry, 1992, Philippart, 1995(a), Philippart, 1995(b), Philippart, 1994(a), Holt et al., 1997, Philippart, 1994(b), Vermaat & Verhagen, 1996, Tubbs & Tubbs, 1982, Tubbs & Tubbs, 1983, Plus et al., 2001
Distribution and Habitat
Distribution in Britain & IrelandFound in estuaries and bays around Britain with extensive populations in the Moray and Cromarty Firths, the Wash, Essex and Thames estuaries, Argyll and Clyde areas. It is also reported from Strangford Lough, Dungarvan Harbour and Dublin Bay in Ireland.
Global distributionFound along the Atlantic coasts of Europe, around the British Isles, from southern Norway to Mauritania. Restricted to brackish conditions e.g. lagoons, river mouths in the Mediterranean and Black Sea. It is the only seagrass in the Caspian and Aral Sea.
Biogeographic rangeNot researchedDepth rangeIntertidal
MigratoryNon-migratory / Resident
Distribution Additional InformationIn non-tidal brackish waters the leaves may be wider than intertidal specimens. In Britain, mixed beds of Zostera noltii and Zostera angustifolia (see Zostera marina review) often occur on the shore. However, the two species occupy different niches, Zostera noltii occurs on hummocks of free draining sediment while Zostera angustifolia is found in hollows that retain standing water at low tide.

The distribution of Zostera noltii in the intertidal may be affected by infaunal deposit feeders. For example, Philliparts (1994a) noted an abrupt cut off between a Zostera noltii bed and an area dominated by Arenicola marina. Zostera noltii was excluded from sediment dominated by Arenicola marina, while the lug worm itself was excluded from the Zostera noltii bed by the presence of a clay layer (Philippart, 1994a). Similar separation has been noted between areas dominated by Zostera noltii or Hediste diversicolor (Hughes et l., 2000).

Substratum preferencesSandy mud, Muddy sand, MudPhysiographic preferencesStrait / sound, Sealoch, Ria / Voe, Estuary, Isolated saline water (Lagoon), Enclosed coast / Embayment
Biological zoneUpper Eulittoral, Mid Eulittoral, Lower Eulittoral, Sublittoral FringeWave exposureSheltered, Very Sheltered, Extremely Sheltered
Tidal stream strength/Water flowModerately Strong (1-3 kn), Weak (<1 kn), Very Weak (negligible)SalinityFull (30-40 psu), Low (<18 psu), Variable (18-40 psu), Reduced (18-30 psu)
Habitat Additional Information
Distribution References Madden et al., 1993, Brazier et al., 1999, Phillips & Menez, 1988, Davison & Hughes, 1998, Hartog den, 1970, Philippart, 1994(a), Hughes et al., 2000, Holt et al., 1997, Rasmussen, 1977, Tubbs & Tubbs, 1983, Anonymous, 1999(p), NBN, 2002
Reproduction/Life History
Reproductive typeVegetative, Protogynous hermaphrodite Developmental mechanismOviparous
Reproductive SeasonMay to SeptemberReproductive Location
Reproductive frequencyAnnual protracted Regeneration potentialNo
Life span1 yearAge 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 monoecious perennials but may be annuals under stressful conditions (Phillips & Menez 1988). Hootsmans et al. (1987) reported that each flowering shoot of Zostera noltii produces 3-4 flowers containing 2-3 seed each. They estimated a potential seed production of 9000/m² based on the maximum density of flowering shoots in their quadrats in the Zandkreek, Netherlands. Most seeds were released in August in the Zandkreek but the actual seed densities were much lower than predicted (Hootsmans et al., 1987). However, the density of flowering shoots is highly variable. 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). Phillips & Menez (1988) state that seedling mortality is extremely high. Fishman & Orth (1996) report that 96% of Zostera marina seeds were lost from uncaged test areas due to transport (dispersal) or predation. Hootsmans et al. (1987) noted that potential recruitment was maximal (32% of seeds) at 30 °C and 10psu, and no recruitment occurred at 30psu. and they estimated that, in 1983 <5% of Zostera noltii plants in the Zandkreek originated from seed. Phillips & Menez (1988) note that seedlings rarely occur within the eelgrass beds except in areas cleared by storms, blow-out or excessive herbivory. Den Hartog (1970) noted that although the seed set was high, Zostera noltii seedlings were rarely seen in the wild, suggesting that vegetative reproduction may be more important than sexual reproduction (Davison & Hughes, 1998). Experimental germination was increased by low salinity (1-10 psu) in Zostera noltii and no germination occurred at salinities above 20 psu, however germination was independent of temperature (Hughes et al., 2000).
Sexual reproduction
Zostera sp. flowers release pollen in long strands, dense enough to remain at the depth they were released for several days, therefore, increasing their chance of pollinating receptive stigmas. Seeds develop within a membranous wall that photosynthesises, developing an oxygen bubble within the capsule, eventually rupturing the capsule to release the seed. Seeds generally sink and may be dispersed by currents and waves (perhaps aided by air bubbles) and the feet or gut of birds.
Methods of dispersal:
  • All parts of the plant may float if they become detached from substratum. Pieces of rhizome or shoots (if displaced by for example storm action) may take root if they settle on suitable substrata (Phillips & Menez, 1988).
  • 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% of Zostera marina 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% 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).
Reproduction References Phillips & Menez, 1988, Davison & Hughes, 1998, Hartog den, 1970, Marta et al., 1996, Nacken & Reise, 2000, Dawes & Guiry, 1992, Hughes et al., 2000, Holt et al., 1997, Churchill et al., 1985, Fishman & Orth, 1996, Olesen & Sand-Jensen, 1993, Hootsmans et al., 1987