Dwarf eelgrass (Zostera (Zosterella) noltei)

Distribution data supplied by the Ocean Biogeographic Information System (OBIS). To interrogate UK data visit the NBN Atlas.

Researched byDr Harvey Tyler-Walters Refereed byDr Leigh Jones
AuthorityHornemann
Other common names- SynonymsZostera nana Roth, Zostera noltii

Summary

Description

Grass-like flowering plant with grass green, long, narrow, ribbon shaped leaves 6-22 cm in length and 0.5-1.5 mm wide with 3 irregularly spaced veins. The tips of the leaves are blunt, notched, often asymmetric, and become indented in older leaves. Leaves shoot from a creeping rhizome, 0.5-2 cm thick, with 1-4 roots per node, which binds the sediment. Leaves shoot in groups of 2-5, encased in a short, open, sheath 0.54 cm long. Several flowers (4-5 male and 4-5 female) occur on a spear-shaped reproductive shoot 2 -25 cm long (usually 10cm). Seeds are smooth, white, and 1.5-2 mm in length (excluding the style). Leaves and rhizomes contain air spaces, lacunae, that aid buoyancy and keep the leaves upright when immersed.

Recorded distribution in Britain and 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.

Habitat

Grows in scattered clumps, dense beds or meadows on intertidal mud or detritus rich fine sand in the intertidal. It is particularly abundant between mean high water neaps and mean low water neaps, often forming a dense belt. Its upper and lower limits shift down shore with decreasing salinity, and in brackish waters (e.g. lagoons, étangs), it may become permanently submerged.

Depth range

Intertidal

Identifying features

  • Leaves grass green in colour.
  • Leaf tips blunt and emarginate (notched), becoming indented in older leaves.
  • Leaves 6 -22 cm long, 0.5-1.5 cm wide with 3 irregularly spaced veins.
  • Leaf sheath short, 0.54 cm, and open with two membranous flaps.
  • Reproductive shoots lateral.
  • Seeds, 1.5-2 mm long (excluding style), white, and smooth.
  • Rhizome 0.5-2 mm thick with 1-4 roots per node.
  • Rhizome with fibre bundles in the innermost layers of the outer cortex.

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).

Listed by

Further information sources

Search on:

NBN WoRMS

Biology review

Taxonomy

PhylumTracheophytaVascular plants (seagrasses, pondweeds, and reeds)
OrderAlismatales
FamilyZosteraceae
GenusZosteraEelgrasses
AuthorityHornemann
Recent SynonymsZostera nana RothZostera noltii

Biology

Typical abundanceHigh density
Male size rangeMale size at maturity
Female size rangeMedium-large(21-50cm)Female size at maturity
Growth formFolioseGrowth rateSee additional text
Body flexibilityHigh (greater than 45 degrees)MobilitySessile
Characteristic feeding methodAutotroph
Diet/food source
Typically feeds onNot relevant
SociabilityNot relevant Environmental positionEpifaunal, Infaunal
DependencyIndependent.
SupportsHost

Numerous epiphytes, some specific to seagrasses and the parasitic fungus Plasmodiophora bicaudata Feldm.

Is the species harmful?No

No text entered

Biology information

Growth
Growth in seagrasses is generally limited by light and affected by temperature (Philliparts, 1995a & b; Marta et al., 1996). Zostera noltei 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 /m was reported in the Zandkreek estuary, Netherlands (Vermaat & Verhagen, 1996). Leaf growth stops in September/October and leaves are shed although Zostera noltei 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 noltei 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 noltei 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 noltei beds in the Thau lagoon, France, to be between 97.5 - 1001.3 mg oxygen /m /h which was within the range reported for other temperate seagrass beds.

Habitat preferences

Physiographic preferencesStrait / sound, Sea loch / Sea lough, Ria / Voe, Estuary, Isolated saline water (Lagoon), Enclosed coast / Embayment
Biological zone preferencesLower eulittoral, Mid eulittoral, Sublittoral fringe, Upper eulittoral
Substratum / habitat preferencesMud, Muddy sand, Sandy mud
Tidal strength preferencesModerately Strong 1 to 3 knots (0.5-1.5 m/sec.), Very Weak (negligible), Weak < 1 knot (<0.5 m/sec.)
Wave exposure preferencesExtremely sheltered, Sheltered, Very sheltered
Salinity preferencesFull (30-40 psu), Low (<18 psu), Reduced (18-30 psu), Variable (18-40 psu)
Depth rangeIntertidal
Other preferencesNo text entered
Migration PatternNon-migratory / resident

Habital Information

In non-tidal brackish waters the leaves may be wider than intertidal specimens. In Britain, mixed beds of Zostera noltei and Zostera angustifolia (see Zostera marina review) often occur on the shore. However, the two species occupy different niches, Zostera noltei 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 noltei in the intertidal may be affected by infaunal deposit feeders. For example, Philliparts (1994a) noted an abrupt cut off between a Zostera noltei bed and an area dominated by Arenicola marina. Zostera noltei was excluded from sediment dominated by Arenicola marina, while the lug worm itself was excluded from the Zostera noltei bed by the presence of a clay layer (Philippart, 1994a). Similar separation has been noted between areas dominated by Zostera noltei or Hediste diversicolor (Hughes et al., 2000).

Life history

Adult characteristics

Reproductive type Vegetative Reproductive frequency Annual protracted
Fecundity (number of eggs) No information Generation time 1-2 years
Age at maturity 1-2 years Season May - September
Life span See additional information

Larval characteristics

Larval/propagule type - Larval/juvenile development Oviparous
Duration of larval stage Not relevant Larval dispersal potential 100 -1000 m
Larval settlement period Not relevant

Life history 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 noltei 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 noltei 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 noltei 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 noltei 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).

Sensitivity reviewHow is sensitivity assessed?

Physical pressures

 IntoleranceRecoverabilitySensitivityEvidence/Confidence
High Low High Moderate

The rhizome occupies the top 20cm of the substratum. Substratum loss will result in the loss of the shoots, rhizome and probably the seed bank. Recoverability will depend on recruitment from other populations. Although Zostera sp. seed dispersal may occur over large distances, high seedling mortality and seed predation may significantly reduce effective recruitment. Holt et al. (1997) suggested that recovery would take between 5-10 years, but in many cases longer. The slow recovery of Zostera populations since the 1920s - 30s outbreak of wasting disease and the continued decline of Zostera noltei beds suggests that, once lost, eelgrass beds take considerable time to re-establish.

High Low High Moderate

Sediment disturbance, siltation, erosion and turbidity resulting from coastal engineering and dredging activities have been implicated in the decline of seagrass beds world wide (Davison & Hughes, 1998; Holt et al., 1997). Seagrasses are intolerant of smothering and typically bend over with addition of sediment and are buried in a few centimetres of sediment (Fonseca, 1992). Zostera sp. are highly intolerant of smothering by epiphytes or algal mats (see nutrients). Recoverability will depend on recruitment from other populations. Although Zostera sp. seed dispersal may occur over large distances, high seedling mortality and seed predation may significantly reduce effective recruitment. Holt et al. (1997) suggested that recovery would take between 5-10 years, but in many cases longer. The slow recovery of Zostera populations since the 1920s - 30s outbreak of wasting disease and the continued decline of Zostera noltei beds suggests that, once lost, eelgrass beds take considerable time to re-establish.

Intermediate High Low Moderate

Increased sediment availability may result in raised eelgrass beds or smothering of the leaves. Decreased sedimentation is likely to result in erosion and loss of the eelgrass beds. Sediment deposited during summer months may be lost again due to winter storms, resuspension by grazing wildfowl, and increased erosion due to die back of leaves and shoots in autumn and winter.
The grazing and digging activity of brent geese and wigeon may increase erosion of intertidal beds during winter months, but in doing so compensate for the sediment deposited during summer months, which may be beneficial to growth of Zostera noltei beds (Nacken & Reise, 2000). The rhizome is probably able to grow through deposited sediment, e.g. Mediterranean Zostera noltei is able to grow upward, through 2 cm of substratum in 4 months (Vermaat et al., 1996). Therefore, Zostera noltei beds are probably tolerant of annual or temporary changes in siltation and sedimentation rates.

However, increased sediment erosion or accretion have been associated with loss of seagrass beds in the Australia, the Mediterranean, the Wadden Sea, and USA. Sediment dynamics and hydrodynamics are key factors in seagrass systems (Asmus & Asmus, 2000a; Davison & Hughes, 1998; Holt et al., 1997). Overall, therefore, seagrass beds are probably intolerant of any activity that changes the sediment regime where the change is greater than expected due to natural events in magnitude or duration and an intolerance of intermediate has been reported. The slow recovery of Zostera populations since the 1920s - 30s outbreak of wasting disease and the continuing decline of Zostera noltii beds suggests that, once lost, eelgrass beds take considerable time to re-establish. However, evidence from grazing studies suggest that Zostera noltii beds can recover within a year after removal of 63% of plant biomass (Nacken & Reise, 2000). Similarly, Dawes & Guiry (1992) regarded Zostera noltei as ephemeral in nature. However, where a bed is stressed by other factors, recovery may be delayed (Holt et al. 1997; Davison & Hughes 1998).
Increased suspended sediment concentrations will also decrease light penetration (see turbidity).

No information
Low Very high Very Low

Zostera noltei is more tolerant of desiccation than other Zostera species, indicated by its intertidal position and ability to colonize well draining sediment. In well -drained areas Zostera noltei may dry out completely between tides (Davison & Hughes, 1998). However, little information on desiccation tolerance was found.

Intermediate High Low Low

Zostera noltei is abundant between mean high water neaps and mean low water neaps. It can survive higher on the shore than Zostera angustifolia although they are often sympatric. Intertidal seagrasses are adapted to leaf and sediment loss due to wave action, grazing and the re-suspension of sediment resulting in high turbidities (Vermaat et al., 1996). Although the intertidal is likely to be affected by high turbidity, Zostera noltei probably makes up for this lack of light by utilising the high levels of light availability when emmersed. It can tolerate higher light intensities than other seagrasses (Vermaat et al., 1996; Davison & Hughes, 1998). Philippart (1995b) noted that although tolerant of high light intensities, its upper shore extent was limited by desiccation tolerance, and the optimal intertidal position of Zostera noltei on a tidal flat near Terschelling, Wadden Sea, was 50% emersion.

A long term change in the emergence regime is likely to increase or reduce the extent of the population in the intertidal. An increase in emergence is likely to reduce its upper extent although this may be compensated for increased growth lower on the shore. Decreased emergence is likely to enable to seagrass bed to expand further up the shore. However, expansion depends on available habitat and competition in infaunal dominated sediments (e.g. Hediste diversicolor or Arenicola marina(Hughes et al., 2000; Philippart, 1994a).

The slow recovery of Zostera populations since the 1920s - 30s outbreak of wasting disease and the continuing decline of Zostera noltei beds suggests that, once lost, eelgrass beds take considerable time to re-establish. However, evidence from grazing studies suggest that Zostera noltii beds can recover within a year after removal of 63% of plant biomass (Nacken & Reise, 2000). Similarly, Dawes & Guiry (1992) regarded Zostera noltei as ephemeral in nature. However, where a bed is stressed by other factors, recovery may be delayed (Holt et al. 1997; Davison & Hughes 1998).

No information
Intermediate High Low Low

Zostera noltei beds typically occur where water flow rates are weak or negligible. Increased flow rates are likely to erode sediment, expose rhizomes and lead to loss of the plants. Increased water flow rates deposit coarser sediments and erode fine sediments resulting in loss of suitable substrata for this species.

The slow recovery of Zostera populations since the 1920s - 30s outbreak of wasting disease and the continuing decline of Zostera noltii beds suggests that, once lost, eelgrass beds take considerable time to re-establish. However, evidence from grazing studies suggest that Zostera noltei beds can recover within a year after removal of 63% of plant biomass (Nacken & Reise, 2000). Similarly, Dawes & Guiry (1992) regarded Zostera noltei as ephemeral in nature. However, where a bed is stressed by other factors, recovery may be delayed (Holt et al. 1997; Davison & Hughes 1998).

No information
Tolerant Not relevant Not sensitive Not relevant

Populations of Zostera noltei occur from the Mediterranean to southern Norway and Zostera sp. are regarded as tolerant of temperatures between about 5 - 30°C. Therefore, they may tolerate the range of temperatures likely in the British Isles (Davison & Hughes, 1998). Intertidal populations may be damaged by frost (Hartog, 1987) and Covey & Hocking (1987) reported defoliation of Zostera noltii in the upper reaches of mudflats in Helford River due to ice formation in the exceptionally cold winter of 1987. However, the rhizomes survived and leaves are usually lost at this time of year due to shedding, storms or grazing with little apparent effect (Nacken & Reise, 2000). Populations at the edge of the range are likely to be more intolerant of temperature change. Phillips & Menez (1988) reported death of seagrass as the result of a thermal plume in Biscayn Bay, Florida that raised ambient temperature by 5°C, however, the species concerned were not cited. Long term temperature increase may increase the relative contribution of sexual reproduction and seed germination to population structure.

No information
Intermediate High Low Low

Increased turbidity due to suspended sediment, humic substances, riverine discharges or phytoplankton growth reduces the light reaching submerged plants. Increase turbidity has been associated with the continued decline of seagrass beds world-wide (Philippart, 1994; Davison & Hughes, 1998; Asmus & Asmus, 2000). However, intertidal Zostera noltei 'escapes' this turbidity since it is able to take advantage of the high light intensities available at low tide (Vermaat et al., 1996). Furthermore, Zostera noltei can store and mobilize carbohydrates and has been reported to be able to tolerate acute light reductions (below 2% of surface irradiance for two weeks) (Peralta et al., 2002). However, Zostera noltei are likely to be more intolerant to chronic increases in turbidity. Philippart (1994b) suggested that the declines in Zostera noltei beds in the Wadden Sea probably occurred at low water level. Permanently submerged population in brackish conditions may be more intolerant of increased turbidity. The slow recovery of Zostera populations since the 1920s - 30s outbreak of wasting disease and the continuing decline of Zostera noltei beds suggests that, once lost, eelgrass beds take considerable time to re-establish. However, evidence from grazing studies suggest that Zostera noltei beds can recover within a year after removal of 63% of plant biomass (Nacken & Reise, 2000). Similarly, Dawes & Guiry (1992) regarded Zostera noltii as ephemeral in nature. However, where a bed is stressed by other factors, recovery may be delayed (Holt et al. 1997; Davison & Hughes, 1998).

No information
High Low High Moderate

Seagrasses require sheltered environments, with gentle longshore currents and tidal flux. Increased wave exposure may increase sediment erosion (see siltation above). Populations present in moderately strong currents may benefit from decreased water flow rates. Small patchy populations or recently established population and seedling may be highly intolerant of increased wave action since they lack an extensive rhizome system.

Recoverability will depend on recruitment from other populations. Although Zostera sp. seed dispersal may occur over large distances, high seedling mortality and seed predation may significantly reduce effective recruitment. Holt et al. (1997) suggested that recovery would take between 5-10 years, but in many cases longer. The slow recovery of Zostera populations since the 1920s - 30s outbreak of wasting disease and the continued decline of Zostera noltei beds suggests that, once lost, eelgrass beds take considerable time to re-establish.

No information
Tolerant Not relevant Not sensitive

The effect of sound waves and vibration on plants is poorly studied. It is likely that sound waves will have little effect at the benchmark levels suggested. Wildfowl are intolerant of disturbance by noise, which may reduce grazing pressure on intertidal Zostera noltei. However, Naken & Reise (2000) suggested that grazing was important for the persistence of Zostera noltei beds, at least in their study area.

Tolerant Not relevant Not sensitive High

Plants have no known visual receptors and are therefore, not sensitive to this factor. Wildfowl are intolerant of disturbance by visual presence of activities, which may reduce grazing pressure on intertidal Zostera noltei. However, Naken & Reise (2000) suggested that grazing was important for the persistence of Zostera noltei beds, at least in their study area.

Intermediate High Low Moderate

Seagrass rhizomes are easily damaged by trampling, anchoring, dredging and other activities that disturb the sediment (Holt et al., 1997; Davison & Hughes, 1998). Small scale sediment disturbance may actually stimulate growth and small patches of sediment allow recolonization by seedlings. Rhizomes are likely to be damaged, leaf blades removed and seeds buried too deep to germinate, by activities such as trampling, anchoring, digging, dredging, power boat and jet-ski wash. For example, damage after the Sea Empress oil spill was reported as limited to the ruts left by clean up vehicles (Jones et al., 2000). Brent geese feed on shoots, rhizomes, and roots, reworking the top centimetre of sediment (8 times in 3 months), and in the process dig pits 3-10cm deep by trampling. As a result, in the Wadden Sea from Sept-Dec (the over-wintering period) Brent geese removed 63% of the plant biomass and pitted 12% of the seagrass bed. However, the bed of Zostera noltii recovered by the following year, and the authors suggested that grazing and bioturbation was necessary for the persistence of the intertidal seagrass beds (Nacken & Reise, 2000). Similarly, several authors have suggested that Zostera sp. can recover from 'normal' levels of wildfowl grazing (Davison & Hughes, 1998). However, suction dredging for cockles in Solway Firth removed Zostera in affected areas while Zostera was abundant in un-dredged areas (Perkins, 1988). Therefore, the passage of a scallop dredge through the seagrass bed (see benchmark) will probably remove a proportion of the seagrass population and intolerance has been assessed as intermediate. Recoverability is likely to be high (see additional information below). However, seagrass beds are likely to be of higher intolerance to repeated scallop dredging or suction dredging.

Intermediate High Low Low

Seagrass rhizomes are easily damaged by trampling, anchoring, dredging and other activities that disturb the sediment (Holt et al., 1997; Davison & Hughes, 1998). The seagrass bed is unlikely to survive displacement. Evidence from grazing studies suggest that Zostera noltei beds can recover within a year after removal of 63% of plant biomass (Nacken & Reise, 2000). Similarly, Dawes & Guiry (1992) regarded Zostera noltii as ephemeral in nature. However, where a bed is stressed by other factors, recovery may be delayed (Holt et al. 1997; Davison & Hughes 1998).
Increased suspended sediment concentrations will also decrease light penetration (see turbidity). However, Phillips & Menez (1988) reported that rhizomes and shoots can root and re-establish themselves if they settle on sediment long enough.

Chemical pressures

 IntoleranceRecoverabilitySensitivityEvidence/Confidence
Intermediate High Low Moderate

There was little information on the effects of chemical contaminants on Zostera noltei and what little was found mainly refers to Zostera marina. Zostera marina is known to accumulate TBT but no damage was observable in the field (Williams et al.,1994). Naphthalene, pentachlorophenol, Aldicarb and Kepone reduce nitrogen fixation and may affect Zostera marina viability. Triazine herbicides (e.g. Irgarol) inhibit photosynthesis and sublethal effects have been detected. Terrestrial herbicides may damage eelgrass beds in the marine environment. For example, the herbicide Atrazine is reported to cause growth inhibition and 50% mortality in Zostera marina exposed to 100 ppb (ng/ l) Atrazine for 21 days (Davison & Hughes 1998). Bester (2000) noted a correlation between raised concentrations of 4 triazine herbicides and areas where Zostera sp. had been lost.

Heavy metal contamination
Low Very high Very Low Low

Little information was found regarding heavy metal concentrations in Zostera noltei however, the following information was found for Zostera marina. The concentration and toxicity of heavy metals in salt marsh plants, including Zostera marina was reviewed by Williams et al., 1994. Growth of Zostera marina is inhibited by 0.32 mg/l Cu and 10 mg/l Hg, but Cd, Zn, Cr and Pb had measurable but less toxic effects (Williams et al., (1994). Davison & Hughes (1998) report that Hg, Ni and Pb reduce nitrogen fixation which may affect viability. However, leaves and rhizomes accumulate heavy metals, especially in winter. Williams et al. (1994) did not observe any damage to Zostera marina in the field. Williams et al. (1994) noted that the major route for uptake of heavy metals was through the leaves and suggested that intertidal populations would accumulate less heavy metals due to their reduced exposure.

Hydrocarbon contamination
High High Moderate Moderate
  • Healthy populations of Zostera can occur in the presence of long term, low level, hydrocarbon effluent, for example in Milford Haven, Wales (Hiscock, 1987; Davison & Hughes, 1998)
  • Zostera noltei is likely to be more vulnerable from direct contact by oil due to its intertidal habitat (Davison & Hughes, 1998; Jones et al., 2000)
  • The Amoco Cadiz oil spill off Roscoff blackened Zostera marina leaves for 1-2 weeks but had little effect on growth, production or reproduction after the leaves were covered in oil for six hours (Jacobs, 1980).
  • Experimental treatment of Zostera noltei with crude oil and dispersants halted growth but had little effect on cover. However, pre-mixed oil and dispersant caused rapid death and significant decline in cover (from 55% to 15% within 1 week suggesting that dispersant treatments should be avoided (Holden & Baker, 1980; Howard et al., 1989; Davison & Hughes, 1998).
  • Oil contamination could result in smothering of the plants, especially in the low energy conditions in which the Zostera noltei is often found (L. Jones, pers. comm.).

The effects of hydrocarbon contamination on Zostera noltii will depend on the type of oil spilled (L. Jones, pers. comm.). Removal of oil intolerant grazers, e.g. gastropods or amphipods, may result in smothering of eelgrasses by epiphytes or algal mats (see nutrients below and LMS.Znol).

Radionuclide contamination
No information Not relevant No information Not relevant

Insufficient
information

Changes in nutrient levels
Intermediate High Low Moderate

Increased nutrient concentrations (nitrates and phosphates) have been implicated in the continued decline of seagrass beds world-wide, either directly or due to eutrophication (Phillips & Menez, 1988; Davison & Hughes, 1998; Philippart, 1994b; Philippart, 1995a, b; Vermaat et al., 1994; Asmus & Asmus, 2000). The following effects on Zostera sp. have been attributed to nutrients and eutrophication.

  • High nitrate concentrations implicated in decline of Zostera marina. Burkholder et al. (1992) demonstrated that nitrate enrichment could cause decline of Zostera marina in poorly flushed areas. In addition they noted that increasing or high temperatures associated with spring exacerbated the adverse effects of nitrate enrichment and that growth and survival were significantly reduced by nutrient enrichment levels of between 3.5 and 35µMolar nitrate/day with the most rapid decline (weeks) at high nitrate levels. Plant loss resulted from death of the meristem tissue.
  • van Katwijk et al. (1999) noted that adverse effects of nitrate were dependent on salinity. Estuarine Zostera marina plants were more intolerant of high nitrate concentration than marine Zostera marina plants at high (30 psu) salinity than at lower salinities (23 psu) and that both populations benefited from nitrate enrichment (0-4 to 6.3 µmMolar nitrate per day) at 23 or 26 psu.
  • Increased growth of epiphytes or blanketing algae, for example:
    • Den Hartog (1994) reported the growth of a dense blanket of Ulva radiata in Langstone Harbour in 1991 that resulted in the loss of 10ha of Zostera marina and Zostera noltei. Subsequently, by summer 1992, the Zostera sp. were absent, however this may have been exacerbated by grazing by Brent geese
    • Philippart (1995b) reported that shading by periphyton reduced incident light reaching the leaves of Zostera noltei by 10-90% and reduced the period of time that net photosynthesis could occur by 2-80% depending on location.
    • Philippart (1995b) estimated that the mud-snail Hydrobia ulvae could remove 25-100% of the periphyton and microphytobenthos, and suggested that the decline of Zostera noltii in the Wadden Sea in the 1970s was in part due to increased periphyton growth due to eutrophication, and a simultaneous decline of the mud-snail population (although mud-snail populations have increased subsequently) (Philippart, 1995a).
  • Encouragement of phytoplankton blooms which increase turbidity and reduce light penetration, although this may be of less significance for intertidal Zostera noltii populations (see above) (Davison & Hughes, 1998).
  • The levels of phenolic compounds in Zostera sp. (involved in disease resistance) are reduced under nutrient enrichment and may increase their susceptibility to infection by wasting disease (Buchsbaum et al., 1990; Burkholder et al., 1992).

Long-term increases in nutrients or eutrophication may result in loss of the intertidal eelgrass beds.

Low Very high Very Low Low

Zostera sp. have a wide tolerance of salinity from 10 - 39 ppt (Davison & Hughes 1998), although den Hartog (1970) suggested a lower salinity tolerance of 5 psu for Zostera sp. Den Hartog (1970) stated that Zostera noltii was a euryhaline species, penetrating estuaries and the Baltic Sea to the average annual isohaline of 9-10 psu. Zostera noltei is probably more tolerant of extremes of salinity than its congeners due to its intertidal habit and Zostera sp. occupy a wide range of salinities, therefore 'low' intolerance has been recorded.

No information
Low Very high Very Low Low

The effects of oxygen concentration on the growth and survivability of Zostera noltei are not reported in the literature. Zostera sp. leaves contain air spaces (lacunae) and oxygen is transported to the roots where it permeates into the sediment, resulting in a oxygenated microzone. This enhances the uptake of nitrogen. The presence of air spaces suggests that seagrass may be tolerant of low oxygen levels in the short term, however, prolonged deoxygenation, especially if combined with low light penetration and hence reduced photosynthesis may have an effect.

Biological pressures

 IntoleranceRecoverabilitySensitivityEvidence/Confidence
Intermediate Very high Low High

A major outbreak of wasting disease resulted in significant declines of Zostera beds on both sides of the Atlantic in 1920s to 1930s, primarily Zostera marina in the subtidal. Wasting disease is thought to be caused by the marine fungus, Labyrinthula macrocystis. The disease causes death of leaves and after 2-3 seasons death of regenerative shoots, rhizomes and loss of up to 90 percent of the population. The disease is less likely at low salinities however, and Zostera noltei was little affected (Rasmussen, 1977; Davison & Hughes, 1998). Decline of intertidal Zostera marina and Zostera noltei beds in the Wadden Sea began in the 1960s and a marked decline in Zostera noltei occurred between 1965 and 1975, presumably due to anthropogenic change (Philippart, 1994b).

Intermediate Low High Moderate

Spartina anglica (a cord grass) is an invasive pioneer species, a hybrid of introduced and native cord grass species. Its rapid growth consolidates sediment, raises mudflats and reduces sediment availability elsewhere. It has been implicated in the reduction of common eelgrass cover in Lindisfarne, Northumberland due to encroachment and changes in sediment dynamics. Wire weed (Sargassum muticum) invades open substratum and may prevent recolonization of areas of eelgrass beds left open by disturbance (Davison & Hughes 1998). Zostera marina and Sargassum muticum may compete for space in the lower shore lagoons of the Solent. However, evidence for competition is conflicting and requires further research. If the invasive species prevents recolonization then recoverability from other factors will be reduced. Intertidal Zostera noltei may be more vulnerable to competition from Spartina sp.

Intermediate High Low Moderate

Wildfowl grazing can consume significant amounts of seagrass and reduce cover mainly in autumn and winter. Tubbs & Tubbs (1983) reported that Brent geese reduced the cover of Zostera marina and Zostera noltei from 60-100% to 5-10% in mid October to mid January in the Solent. Grazing is probably part of the natural seasonal fluctuation in seagrass cover and Zostera sp. can recover from normal grazing (Naken & Reise, 2000; Davison & Hughes, 1998). Zostera noltei is the preferred food of the dark-bellied Brent goose (Branta bernicla). Brent geese feed on shoots, rhizomes and roots, reworking the top centimetre of sediment (8 times in 3 months), and in the process dig pits 3-10cm deep by trampling. As a result, in the Wadden Sea from Sept-Dec (the over-wintering period) Brent geese removed 63% of the plant biomass and pitted 12% of the seagrass bed. However, the bed of Zostera noltei recovered by the following year, and the authors suggested that grazing and bioturbation was necessary for the persistence of the intertidal seagrass beds (Nacken & Reise, 2000). However, where a bed is stressed by other factors it may not be able to withstand grazing (Holt et al. 1997; Davison & Hughes 1998). For example, seagrass rhizomes are easily damaged by trampling, anchoring, dredging and other activities that disturb the sediment. A seagrass bed is unlikely to survive displacement or extraction, although Phillips & Menez (1988) reported that rhizomes and shoots can root and re-establish themselves if they settle on sediment long enough. Therefore, Zostera noltei beds have been considered to be of 'intermediate' intolerance to extraction.

High Low High High

Zostera sp. are regarded as very intolerant of hydraulic bivalve fishing in the UK and Wadden Sea (Holt et al., 1997; Davison & Hughes, 1998; Philippart, 1994b). Cockles and Zostera noltei are frequently associated and intertidal beds may be more vulnerable (Holt et al., 1997). Hydraulic dredging is likely to break up and remove rhizomes. It was suggested that hydraulic harvesting of cockles in the Solway Firth could cause widespread damage or eradicate Zostera sp. from the bay (Perkins, 1988). Digging and dredging for the American hard-shell clam (Mercenaria mercenaria had a significant effect on the eelgrass beds (Cox, 1991; Eno et al., 1997). In the Dutch Wadden Sea, seagrass is hardly found where cockles are normally fished (Dankers & de Vlas, 1992). Recovery was severely restricted especially where no rhizomes and roots were left in the sediment (De Jong & de Jong, 1992; Philippart, 1994b).

Additional information

No text entered.

Importance review

Policy/legislation

IUCN Red ListLeast Concern (LC)

Status

National (GB) importanceNationally scarceGlobal red list (IUCN) categoryLeast Concern (LC)

Non-native

Native-
Origin- Date ArrivedNot relevant

Importance information

Zostera noltei is included in a Habitat Action Plan under the UK Biodiversity Action Plan. Seagrass beds are recognised internationally as important coastal ecosystems (Asmus & Asmus, 2000a & b).
  • seagrass beds are highly productive ecosystems which are utilised directly by grazers such as wildfowl and export their productivity in the form of detritus to support surrounding benthic communities;
  • seagrass support a diverse epifauna, epiflora and infauna, although intertidal beds are have lower species diversity than subtidal beds;
  • seagrass beds are important sediment traps, stabilize the sediment, reduce the incident wave energy and may act as a natural coastal defence (Davison & Hughes, 1998);
  • loss of seagrass beds have resulted in profound changes in the material budget, food web and ecosystem (Asmus & Asmus, 2000a & b);
  • Zostera is an important component of the diet of Brent geese (Branta bernicla), wigeon (Anas penelope), mute and whooper swans (Cygnus olor and Cygnus cygnus);
  • the Brent geese population in Europe declined as a result of the decline in eelgrass populations due to wasting disease (den Hartog, 1970; Phillips & Menez, 1988; Davison & Hughes, 1998; Asmus & Asmus, 2000b).
Zostera noltei has replaced Zostera marina as the preferred food species for Brent geese (Tubbs & Tubbs, 1982; Davison & Hughes, 1998).

Sea grasses have been put to a number of uses in the past for example, sound-proofing, insulation, roofing thatch, binding soil, packaging, basket weaving and in the manufacture of 'coir' matting (see Kuelan, 1999 for review).

Bibliography

  1. Anonymous, 1999p. Seagrass beds. Habitat Action Plan. In UK Biodiversity Group. Tranche 2 Action Plans. English Nature for the UK Biodiversity Group, Peterborough., English Nature for the UK Biodiversity Group, Peterborough.

  2. Asmus, H. & Asmus, R., 2000a. ECSA - Workshop on intertidal seagrass beds and algal mats: organisms and fluxes at the ecosystem level. (Editorial). Helgoland Marine Research, 54, 53-54.

  3. Asmus, H. & Asmus, R., 2000b. Material exchange and food web of seagrasses beds in the Sylt-Rømø Bight: how significant are community changes at the ecosystem level? Helgoland Marine Research, 54, 137-150.

  4. Bester, K., 2000. The effects of pesticides on seagrass beds. Helgoland Marine Research, 54, 95-98.

  5. Brazier, D.P., Holt, R.H.F., Murray, E. & Nichols, D.M., 1999. Marine Nature Conservation Review Sector 10. Cardigan Bay and North Wales: area summaries. Peterborough: Joint Nature Conservation Committee. [Coasts and seas of the United Kingdom. MNCR Series.]

  6. Buchsbaum, R.N., Short, F.T. & Cheney, D.P., 1990. Phenolic-nitrogen interactions in eelgrass Zostera marina: possible implications for disease resistance. Aquatic Botany, 37, 291-297.

  7. Burkholder, J.M., Mason, K.M. & Glasgow, H.B. Jr., 1992. Water-column nitrate enrichment promotes decline of eelgrass Zostera marina: evidence from seasonal mesocosm experiments. Marine Ecology Progress Series, 81, 163-178.

  8. Churchill, A.C., Nieves, G. & Brenowitz, A.H., 1985. Floatation and dispersal of eelgrass seeds by gas bubbles. Estuaries, 8, 352-354.

  9. Covey, R. & Hocking, S., 1987. Helford River Survey. Report for the Heinz, Guardians of the Countryside and World Wide Fund for Nature, 121 pp.

  10. Cox, J., 1991. Dredging for the American hard-shell clam - implications for nature conservation. Ecosystems. A Review of Conservation, 12, 50-54.

  11. Dankers, N. & de Vlas, J., 1992. Multifunctioneel beheer in de Waddenzee, integratie van natuurbeheer en schelpdiervisserij. Institute for Forestry and Nature Research, RIN Report, no. 92/15, 18pp.

  12. Davison, D.M. & Hughes, D.J., 1998. Zostera biotopes: An overview of dynamics and sensitivity characteristics for conservation management of marine SACs, Vol. 1. Scottish Association for Marine Science, (UK Marine SACs Project)., Scottish Association for Marine Science, (UK Marine SACs Project),Vol. 1., http://www.english-nature.org.uk/uk-marine

  13. Dawes, C.J. & Guiry, M.D., 1992. Proximate constituents in the seagrasses Zostera marina and Z. noltii in Ireland. Marine Ecology, 13, 307-315.

  14. de Jonge, V.N.& de Jonge, D.J., 1992. Role of tide, light and fisheries in the decline of Zostera marina. Netherlands Institute of Sea Research Publications Series no. 20, pp. 161-176.

  15. Den Hartog, C., 1970. The sea-grasses of the world. Amsterdam: North Holland Publishing Company.

  16. Den Hartog, C., 1994. Suffocation of a littoral Zostera bed by Enteromorpha radiata. Aquatic Botany, 47, 21-28.

  17. Eno, N.C., Clark, R.A. & Sanderson, W.G. (ed.) 1997. Non-native marine species in British waters: a review and directory. Peterborough: Joint Nature Conservation Committee.

  18. Fishman, J.R. & Orth, R.J., 1996. Effects of predation on Zostera marina L. seed abundance. Journal of Experimental Marine Biology and Ecology, 198, 11-26.

  19. Hiscock, S., 1987. A brief account of the algal flora of Zostera marina beds in the Isle of Scilly. In Sublittoral monitoring in the Isles of Scilly 1985 & 1986 (ed. R. Irving). Nature Conservancy Council, Peterborough.

  20. Holden, P. & Baker, J.M., 1980. Dispersant-treated compared with untreated crude oil. Experiments with oil and dispersants on the seagrass Zostera noltii. Report to the Advisory Committee on Pollution of the Sea, Field Studies Council.

  21. Holt, T.J., Hartnoll, R.G. & Hawkins, S.J., 1997. The sensitivity and vulnerability to man-induced change of selected communities: intertidal brown algal shrubs, Zostera beds and Sabellaria spinulosa reefs. English Nature, Peterborough, English Nature Research Report No. 234.

  22. Hootsmans, M.J.M., Vermaat, J.E. & Vierssen, van W., 1987. Seed-bank development, germination and early seedling survival of two seagrass species from the Netherlands: Zostera marina L. and Zostera noltii Hornem. Aquatic Botany, 28 (3), 275-285

  23. Howard, S., Baker, J.M. & Hiscock, K., 1989. The effects of oil and dispersants on seagrasses in Milford Haven. In Ecological Impacts of the Oil Industry,(ed. B. Dicks), pp. 61-96. Chichester: John Wiel & Sons Ltd. for the Institute of Petroleum, London.

  24. Hughes, R.G., Lloyd, D., Ball, L., Emson, D., 2000. The effects of the polychaete Nereis diversicolor on the distribution and transplantation success of Zostera noltii. Helgoland Marine Research, 54, 129-136.

  25. Jacobs, R.P.W.M., 1980. Effects of the Amoco Cadiz oil spill on the seagrass community at Roscoff with special reference to the benthic infauna. Marine Ecology Progress Series, 2, 207-212.

  26. Jones, L.A., Hiscock, K. & Connor, D.W., 2000. Marine habitat reviews. A summary of ecological requirements and sensitivity characteristics for the conservation and management of marine SACs. Joint Nature Conservation Committee, Peterborough. (UK Marine SACs Project report.). Available from: http://www.ukmarinesac.org.uk/pdfs/marine-habitats-review.pdf

  27. Katwijk van, M.M., Schmitz, G.H.W., Gasseling, A.P., & Avesaath van, P.H., 1999. Effects of salinity and nutrient load and their interaction on Zostera marina. Marine Ecology Progress Series, 190, 155-165.

  28. Kuelan, van M., 1999. Human uses of seagrass. http://possum.murdoch.edu.au/~seagrass/seagrass_uses.html, 2000-01-01

  29. Madden, B., Jennings, E. & Jeffrey, D.W., 1993. Distribution and ecology of Zostera in Co. Dublin. The Irish Naturalists' Journal, 24, 303-310.

  30. Marta, N., Cebrian, J., Enriquez, S. & Duarte, C.M., 1996. Growth patterns of western Mediterranean seagrasses: species specific responses to seasonal forcing. Marine Ecology Progress Series, 133, 203-215.

  31. Nacken, M. & Reise, K., 2000. Effects of herbivorous birds on intertidal seagrass beds in the northern Wadden Sea. Helgoland Marine Research, 54, 87-94.

  32. National Biodiversity Network (NBN) Atlas website. Available from: http://www.nbnatlas.org.  Accessed 01 April 2017

  33. Olesen, B. & Sand-Jensen, K., 1993. Seasonal acclimation of eelgrass Zostera marina growth to light. Marine Ecology Progress Series, 94, 91-99.

  34. Peralta, G., Pérez-Lloréns, J.L., Hernández, I. & Vergara, J.J., 2002. Effects of light availability on growth, architecture and nutrient content of the seagrass Zostera noltii Hornem. Journal of Experimental Marine Biology and Ecology, 269, 9-26.

  35. Perkins, E.J., 1988. The impact of suction dredging upon the population of cockles Cerastoderma edule in Auchencairn Bay. Report to the Nature Conservancy Council, South-west Region, Scotland, no. NC 232 I).

  36. Philippart, C.J.M, 1994a. Interactions between Arenicola marina and Zostera noltii on a tidal flat in the Wadden Sea. Marine Ecology Progress Series, 111, 251-257.

  37. Philippart, C.J.M, 1994b. Eutrophication as a possible cause of decline in the seagrass Zostera noltii of the Dutch Wadden Sea. http://www.nioz.nl/en/deps/mee/katja/seagrass.htm, 2000-10-23

  38. Philippart, C.J.M, 1995a. Effect of periphyton grazing by Hydrobia ulvae on the growth of Zostera noltii on a tidal flat in the Dutch Wadden Sea. Marine Biology, 122, 431-437.

  39. Philippart, C.J.M, 1995b. Seasonal variation in growth and biomass of an intertidal Zostera noltii stand in the Dutch Wadden Sea. Netherlands Journal of Sea Research, 33, 205-218.

  40. Phillips, R.C., & Menez, E.G., 1988. Seagrasses. Smithsonian Contributions to the Marine Sciences, no. 34.

  41. Plus, M., Deslous-Paoli, J-M., Auby, I. & Dagault, F., 2001. Factors influencing primary production of seagrass beds (Zostera noltii Hornem.) in the Thau lagoon (French Mediterranean coast). Journal of Experimental Marine Biology and Ecology, 259, 63-84.

  42. Rasmussen, E., 1977. The wasting disease of eelgrass (Zostera marina) and its effects on environmental factors and fauna. In Seagrass ecosystems - a scientific perspective, (ed. C.P. McRoy, & C. Helfferich), pp. 1-51.

  43. Tubbs, C.R. & Tubbs, J.M., 1982. Brent geese (Branta bernicla) and their food in the Solent, southern England. Biological Conservation, 23, 33-54.

  44. Tubbs, C.R. & Tubbs, J.M., 1983. The distribution of Zostera and its exploitation by wildfowl in the Solent, southern England. Aquatic Botany, 15, 223-239.

  45. Vermaat, J.E. & Verhagen, F.C.A., 1996. Seasonal variation in the intertidal seagrass Zostera noltii Hornem.: coupling demographic and physiological patterns. Aquatic Botany, 52, 259-281.

  46. Vermaat, J.E., Agawin, N.S.R., Fortes, M.D., Uri, J.S., Duarte, C.M., Marbà, N., Enríquez, S. & Vierssen van, W., 1997. The capacity of seagrasses to survive increased turbidity and siltation: the significance of growth form and light use. Ambio, 26 (8), 499-504.

  47. Williams, T.P., Bubb, J.M., & Lester, J.N., 1994. Metal accumulation within salt marsh environments: a review. Marine Pollution Bulletin, 28, 277-290.

Citation

This review can be cited as:

Tyler-Walters, H., 2005. Zostera (Zosterella) noltei Dwarf eelgrass. In Tyler-Walters H. and Hiscock K. (eds) Marine Life Information Network: Biology and Sensitivity Key Information Reviews, [on-line]. Plymouth: Marine Biological Association of the United Kingdom. Available from: http://www.marlin.ac.uk/species/detail/1409

Last Updated: 14/10/2005