BIOTIC Species Information for Zostera noltii
|Researched by||Dr Harvey Tyler-Walters||Data supplied by||MarLIN|
|Refereed by||Dr Leigh Jones|
|Scientific name||Zostera noltii||Common name||Dwarf eelgrass|
|MCS Code||None||Recent Synonyms||Zostera nana (Roth)|
|Additional Information||Like 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,|
|Typical food types||Not relevant||Habit||Attached|
|Bioturbator||Not relevant||Flexibility||High (>45 degrees)|
|Height||Growth Rate||See additional text|
|Adult dispersal potential||10-100m||Dependency||Independent|
|General Biology Additional Information||Growth
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).
|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 & Ireland||Found 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 distribution||Found 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 range||Not researched||Depth range||Intertidal|
|Migratory||Non-migratory / Resident|
|Distribution Additional Information||In 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 preferences||Sandy mud
|Physiographic preferences||Strait / sound
Ria / Voe
Isolated saline water (Lagoon)
Enclosed coast / Embayment
|Biological zone||Upper Eulittoral
|Tidal stream strength/Water flow||Moderately Strong (1-3 kn)
Weak (<1 kn)
Very Weak (negligible)
|Salinity||Full (30-40 psu)
Low (<18 psu)
Variable (18-40 psu)
Reduced (18-30 psu)
|Habitat Preferences 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,|
|Reproductive Season||May to September||Reproductive Location|
|Reproductive frequency||Annual protracted||Regeneration potential||No|
|Life span||1 year||Age at reproductive maturity||1-2 years|
|Generation time||1-2 years||Fecundity||Insufficient information|
|Egg/propagule size||Fertilization type|
|Reproduction Preferences Additional Information||Zostera 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).
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:
|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,|