|Researched by||Dr Harvey Tyler-Walters||Refereed by||Dr Leigh Jones|
|Other common names||-||Synonyms||Zostera marina|
Grass like flowering plant with dark green, long, narrow, ribbon shaped leaves 20-50 cm in length (exceptionally up to 2 m long) with rounded tips. Leaves shoot from a creeping rhizome that binds the sediment. Leaves and rhizomes contain air spaces, lacunae, that aid buoyancy. Numerous flowers occur on a reproductive shoot similar to those of terrestrial grasses. Forms dense swards in the subtidal, supports a diverse fauna and flora and may act as a nursery for fish and shellfish.
Other 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.
|Phylum||Tracheophyta||Vascular plants (seagrasses, pondweeds, and reeds)|
|Recent Synonyms||Zostera marina|
|Typical abundance||High density|
|Male size range|
|Male size at maturity|
|Female size range||Medium-large(21-50cm)|
|Female size at maturity|
|Characteristic feeding method||Autotroph|
|Typically feeds on||Not relevant|
|Dependency||No text entered.|
Entocladia perforans, a green alga; Rhodophysema georgii, a crustose red alga; and brown algae Halothrix lumbricalis, Leblondiella densa, Myrionema magnusii, Cladosiphon zosterae, and Punctaria crispata.
|Is the species harmful?||No information|
The 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:
|Physiographic preferences||Estuary, Isolated saline water (Lagoon), Enclosed coast / Embayment|
|Biological zone preferences||Sublittoral fringe, Upper infralittoral|
|Substratum / habitat preferences||Gravel / shingle, Muddy gravel, Muddy sand, Sandy mud|
|Tidal strength preferences||Very Weak (negligible), Weak < 1 knot (<0.5 m/sec.)|
|Wave exposure preferences||Sheltered, Very sheltered|
|Salinity preferences||Variable (18-40 psu)|
|Depth range||0 to 5m|
|Migration Pattern||Non-migratory / resident|
|Reproductive frequency||Annual episodic|
|Fecundity (number of eggs)||100-1,000|
|Generation time||1-2 years|
|Age at maturity||1-2 yr.|
|Season||May - September|
|Life span||20-100 years|
|Duration of larval stage||Not relevant|
|Larval dispersal potential||100 -1000 m|
|Larval settlement period|
The MarLIN sensitivity assessment approach used below has been superseded by the MarESA (Marine Evidence-based Sensitivity Assessment) approach (see menu). The MarLIN approach was used for assessments from 1999-2010. The MarESA approach reflects the recent conservation imperatives and terminology and is used for sensitivity assessments from 2014 onwards.
|High||Very low / none||Very 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 marina seed dispersal may occur over large distances, high seedling mortality and seed predation may significantly reduce effective recruitment. The slow recovery of Zostera populations since the 1920s - 30s outbreak of wasting disease suggests that, once lost, eelgrass beds take considerable time to re-establish.|
|High||Very low / none||Very 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). Recoverability will depend on recruitment from other populations. Although Zostera marina seed dispersal may occur over large distances, high seedling mortality and seed predation may significantly reduce effective recruitment. The slow recovery of Zostera populations since the 1920s - 30s outbreak of wasting disease suggests that, once lost, eelgrass beds take considerable time to re-establish.|
|Increased sediment erosion or accretion have been associated with loss of seagrass beds in the Australia, the Mediterranean and USA. Increased sediment availability may result in raised eelgrass beds, more likely to be exposed to low tide, desiccation and high temperatures. Seagrass beds demonstrate a balance of sediment accretion and erosion. 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. Seagrass beds should be considered intolerant of any activity that changes the sediment regime where the change is greater than expected due to natural events.|
|Zostera marina is mainly subtidal and intolerant of desiccation compared to other species of eelgrass. If exposed at low tide the shoot bases are stiff and upright for a few centimetres, and leaf bases will be killed by 30 min exposure on a warm, sunny day (Holt et al. 1997). Even short periods of drying kills the flowers. However, if the rhizomes are undamaged the leaves will grow back but repeated exposure to desiccation may exhaust the energy stores in the rhizomes. Zostera marina may be more intolerant of activities that cause the sediment to drain or dry.|
|Zostera marina that extend into the intertidal are likely to be highly intolerant of change increase in the emergence time (see desiccation).|
|Seagrasses require sheltered environments, with gentle longshore currents and tidal flux. Where populations are found in moderately strong currents they are smaller, patchy and vulnerable to storm damage and blow outs. Increased water flow may also increase sediment erosion (see siltation above). Populations present in moderately strong currents may benefit from decreased water flow rates.|
|Tolerant||Not relevant||Not sensitive||Moderate|
|Populations of Zostera marina occur from the Mediterranean to Arctic Circle and are regarded as tolerant between about 5 - 30 deg C and tolerant of up to 20 deg C without stress. Therefore, they may tolerate the range of temperatures likely in the British Isles (Davison & Hughes 1998). However, intertidal populations may be damaged by frost (Hartog 1987). Populations at the edge of the range are likely to be more intolerant of temperature change. Phillips & Menez (1988) report death of seagrass as the result of a thermal plume in Biscayn Bay, Florida that raised ambient temperature by 5 degrees 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.|
|Light attenuation limits the depth to which Zostera marina can grow and is a requirement for photosynthesis. Turbidity resulting from dredging and eutrophication caused a massive decline of Zostera populations in the Wadden Sea (Geisen et al. 1990). Seagrass populations are likely to survive increased turbidity for a month however prolonged increase in light attenuation will probably result in loss or damage of the population.|
|Seagrasses require sheltered environments, with gentle longshore currents and tidal flux. Where populations are found in moderately strong currents they are smaller, patchy and vulnerable to storm damage and blow outs. Increased wave exposure may also 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.|
|Tolerant||Not relevant||Not sensitive|
|The effect of sound waves and vibration on plants is poorly studied. However, it is likely that sound waves will have little effect at the benchmark levels suggested.|
|Tolerant||Not relevant||Not sensitive|
|Continuous shading will affect photosynthesis and therefore viability. However, occasional shading caused by surface movements of vessels at the level of this benchmark is unlikely to have an effect on seagrass beds.|
|Small scale sediment disturbance may stimulate growth and small patches of sediment allow recolonization by seedlings (Davison & Hughes, 1998). However, seagrasses are not physically robust and rhizomes are likely to be damaged, and seeds buried too deep to germinate, by activities such as trampling, anchoring, digging, dredging, power boat and jet-ski wash (Fonseca, 1992). Suction dredging for cockles in Solway Firth removed Zostera in affected areas while Zostera was abundant in un-dredged areas (Perkins, 1988). Physical disturbance and removal of plants can lead to increased patchiness and destabilization of the seagrass bed, which in turn can lead to reduced sedimentation within the seagrass bed, increased erosion, and loss of larger areas of Zostera(Davison & Hughes, 1998). Therefore, the impact from a scallop dredge is likely to remove a proportion of the population and result in increased erosion of the bed. Therefore, intolerance has been recorded as intermediate.|
|Seagrass rhizomes are easily damaged by trampling, anchoring, dredging and other activities that disturb the sediment. The seagrass bed is unlikely to survive displacement. However, Phillips & Menez (1988) reported that rhizomes and shoots can root and re-establish themselves if they settle on sediment long enough.|
|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 percent mortality in Zostera marina exposed to 100 ppb (ng/ l) Atrazine for 21 days (Davison & Hughes 1998).|
|Low||Very high||Very Low||Moderate|
|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.|
|Low||Very high||Very Low||Moderate|
|No information||No information||No information||Not relevant|
|Where nutrients are limiting, additional low levels of nutrients may improve growth of Zostera marina . The reported effects of nutrient enrichment include:
|Low||Very high||Very Low||Low|
|Zostera sp. have a wide tolerance of salinity from 10 - 39 ppt (Davison & Hughes 1998). Germination in Zostera marina occurs over a range of salinities.|
|Low||Very high||Very Low|
|The effects of oxygen concentration on the growth and survivability of Zostera marina are not reported in the literature. Zostera marina 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.|
|A major outbreak of wasting disease resulted in significant declines of Zostera marina beds in 1920s to 1930s. Wasting disease is thought to be caused by the marine fungus, Labyrinthula macrocystis. The disease is less likely at low salinities however, Zostera marina prefers full salinities. 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.|
|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 prevent recolonization then recoverability from other factors will be reduced.|
|Wildfowl grazing can consume significant amounts of seagrass and reduce cover mainly in autumn and winter. Grazing is probably part of the natural seasonal fluctuation in seagrass cover and Zostera sp. can recover from normal grazing. However, where a bed is stress by other factors it may not be able to withstand grazing (Holt et al. 1997; Davison & Hughes 1998). Eelgrass rhizomes are easily damaged by trampling, anchoring, dredging and other activities that disturb the sediment. The seagrass bed is unlikely to survive displacement or extraction. However, Phillips & Menez (1988) reported that rhizomes and shoots can root and re-establish themselves if they settle on sediment long enough.|
|Seagrass rhizomes are easily damaged by trampling, anchoring, dredging and other activities that disturb the sediment. Seeds may be buried too deep to germinate. Mechanical dredging of cockles in Solway Firth, in intertidal Zostera beds, resulted in the loss of the seagrass bed and was closed. Dredging for bivalves has been implicated in the decline of seagrass beds in the Dutch, Wadden Sea. Damage after the Sea Empress oil spill was reported as limited to the ruts left by clean up vehicles.|
|Berne Convention||Appendix I|
|IUCN Red List||Least Concern (LC)|
|National (GB) importance||Not rare/scarce||Global red list (IUCN) category||Least Concern (LC)|
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.
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.
Churchill, A.C., Nieves, G. & Brenowitz, A.H., 1985. Floatation and dispersal of eelgrass seeds by gas bubbles. Estuaries, 8, 352-354.
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. Available from: http://ukmpa.marinebiodiversity.org/uk_sacs/pdfs/zostera.pdf
Den Hartog, C., 1970. The sea-grasses of the world. Amsterdam: North Holland Publishing Company.
Den Hartog, C., 1987. "Wasting disease" another dynamic phenomena in Zostera beds. Aquatic Botany, 27, 3 -14.
Den Hartog, C., 1994. Suffocation of a littoral Zostera bed by Enteromorpha radiata. Aquatic Botany, 47, 21-28.
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.
Fonseca, M.S., 1992. Restoring seagrass systems in the United States. In Restoring the Nation's Marine Environment (ed. G.W. Thayer), pp. 79 -110. Maryland: Maryland Sea Grant College.
Giesen, W.B.J.T., Katwijk van, M.M., Hartog den, C., 1990a. Eelgrass condition and turbidity in the Dutch Wadden Sea. Aquatic Botany, 37, 71-95. DOI https://doi.org/10.1016/0304-3770(90)90065-S
Guiry, M.D. & Nic Dhonncha, E., 2000. AlgaeBase. World Wide Web electronic publication http://www.algaebase.org, 2000-01-01
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.
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
Kuelan, van M., 1999. Human uses of seagrass. http://possum.murdoch.edu.au/~seagrass/seagrass_uses.html, 2000-01-01
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).
Phillips, R.C., & Menez, E.G., 1988. Seagrasses. Smithsonian Contributions to the Marine Sciences, no. 34.
Reusch, T.B.H., Stam, W.T., & Olsen, J.C. 1998. Size and estimated age of genets in eelgrass, Zostera marina, assessed with microsatellite markers. Marine Biology, 133, 519-525.
Rucklehaus, M.H., 1998. Spatial scale of genetic structure and an indirect estimate of gene flow in eelgrass, Zostera marina. Evolution, 52, 330-343
Stewart, A., Pearman, D.A. & Preston, C.D., 1994. Scarce plants in Britain. Joint Nature Conservation Committee, Peterborough.
Williams, T. P., Bubb, J. M. & Lester, J. N., 1994. Metal accumulation within salt-marsh environments - a review. Marine Pollution Bulletin, 28 (5), 277-290. DOI https://doi.org/10.1016/0025-326x(94)90152-x
Botanical Society of Britain & Ireland, 2018. Other BSBI Scottish data up to 2012. Occurrence dataset: https://doi.org/10.15468/2dohar accessed via GBIF.org on 2018-09-25.
Botanical Society of Britain & Ireland, 2018. Scottish SNH-funded BSBI records. Occurrence dataset: https://doi.org/10.15468/llasrt accessed via GBIF.org on 2018-09-25.
Botanical Society of Britain & Ireland, 2018. Welsh BSBI data (ex-VPDB dataset) at hectad resolution. Occurrence dataset: https://doi.org/10.15468/rsvnif accessed via GBIF.org on 2018-09-25.
Bristol Regional Environmental Records Centre, 2017. BRERC species records recorded over 15 years ago. Occurrence dataset: https://doi.org/10.15468/h1ln5p accessed via GBIF.org on 2018-09-25.
Centre for Environmental Data and Recording, 2018. Ulster Museum Marine Surveys of Northern Ireland Coastal Waters. Occurrence dataset https://www.nmni.com/CEDaR/CEDaR-Centre-for-Environmental-Data-and-Recording.aspx accessed via NBNAtlas.org on 2018-09-25.
Centre for Environmental Data and Recording, 2018. Ulster Wildlife Snorkel Safaris. Occurrence dataset: https://www.nmni.com/CEDaR/CEDaR-Centre-for-Environmental-Data-and-Recording.aspx accessed via NBNAtlas.org on 2018-09-25.
Fenwick, 2018. Aphotomarine. Occurrence dataset http://www.aphotomarine.com/index.html Accessed via NBNAtlas.org on 2018-10-01
Isle of Wight Local Records Centre, 2017. Isle of Wight Notable Species. Occurrence dataset: https://doi.org/10.15468/sm4ety accessed via GBIF.org on 2018-09-27.
Manx Biological Recording Partnership, 2017. Isle of Man wildlife records from 01/01/2000 to 13/02/2017. Occurrence dataset: https://doi.org/10.15468/mopwow accessed via GBIF.org on 2018-10-01.
Manx Biological Recording Partnership, 2018. Isle of Man historical wildlife records 1990 to 1994. Occurrence dataset: https://doi.org/10.15468/aru16v accessed via GBIF.org on 2018-10-01.
Manx Biological Recording Partnership, 2018. Isle of Man historical wildlife records 1990 to 1994. Occurrence dataset:https://doi.org/10.15468/aru16v accessed via GBIF.org on 2018-10-01.
National Trust, 2017. National Trust Species Records. Occurrence dataset: https://doi.org/10.15468/opc6g1 accessed via GBIF.org on 2018-10-01.
NBN (National Biodiversity Network) Atlas. Available from: https://www.nbnatlas.org.
Norfolk Biodiversity Information Service, 2017. NBIS Records to December 2016. Occurrence dataset: https://doi.org/10.15468/jca5lo accessed via GBIF.org on 2018-10-01.
OBIS (Ocean Biodiversity Information System), 2023. Global map of species distribution using gridded data. Available from: Ocean Biogeographic Information System. www.iobis.org. Accessed: 2023-01-31
Royal Botanic Garden Edinburgh, 2018. Royal Botanic Garden Edinburgh Herbarium (E). Occurrence dataset: https://doi.org/10.15468/ypoair accessed via GBIF.org on 2018-10-02.
South East Wales Biodiversity Records Centre, 2018. SEWBReC Vascular Plants (South East Wales). Occurrence dataset: https://doi.org/10.15468/7qjujd accessed via GBIF.org on 2018-10-02.
South East Wales Biodiversity Records Centre, 2018. Dr Mary Gillham Archive Project. Occurance dataset: http://www.sewbrec.org.uk/ accessed via NBNAtlas.org on 2018-10-02
Suffolk Biodiversity Information Service., 2017. Suffolk Biodiversity Information Service (SBIS) Dataset. Occurrence dataset: https://doi.org/10.15468/ab4vwo accessed via GBIF.org on 2018-10-02.
This review can be cited as:
Last Updated: 02/08/2008