Holy-leaved naiad (Najas marina) - Species Action Plan

Holly-leaved naiad is a dioecious (i.e. having male and female flowers on separate plants) annual which grows completely submerged in shallow lakes. It is usually found in meso-eutrophic water over deep substrates of silt or peaty mud in water deeper than 0.2m.
Ref 1/S29 Species Action Plan 29
Plan Author: English Nature
Plan Co-ordinator: English Nature
Review complete January 2003

 

Action Plan Summary

Current Status

National Status

  • In the UK it has only been found in the Norfolk Broads. It is protected under Schedule 8 of the Wildlife and Countryside Act 1981 

Norfolk Status

  • It occurs regularly at Upton Broad, Hickling Broad and Martham Broad, with transient populations in several other broads and newly-created turf ponds. 
  • Current populations are confined to the Broads but historic data gathered through analysis of sediments in lakes across Norfolk confirm that it used to be more widely distributed.

The main strongholds in the Broads are at Upton Broad, Hickling Broad (particularly in Heigham Corner) and Martham Broad. In 1999 plants were additionally recorded at Cockshoot, Hoveton Little Broad, Hoveton Great Broad, Horsey Mere and Strumpshaw Broad. There have been occasional records from many parts of the Broads system but these tend to come and go as there are never enough plants growing at any one time to develop a viable population.

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Current factors causing loss or decline in Norfolk

Eutrophication of water bodies caused by agricultural run off and sewage discharge. Turbulence and pollution associated with boat traffic on the Broads.

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Current Action in Norfolk

The populations of this plant are being monitored regularly. The three permanent sites are nature reserves in SSSIs. The turf pond programme is creating new suitable habitat. The Broads are within an ESA. Research is being undertaken into the ecology and requirements of this species at the University of East Anglia. Work is continuing at the Royal Botanic Gardens, Kew to determine optimum conditions for seed storage. 

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Action Plan Objectives and Targets

National

  • Maintain at all known sites
  • Survey to confirm status of the species in the UK
  • Observe re-colonisation of five water bodies (individually named rivers or broads) adjacent to existing sites by 2004

Norfolk

  • Maintain at all known sites in the Broads
  • Survey to confirm status of the species in the Broads
  • Observe re-colonisation of five water bodies (individually named rivers or broads) adjacent to existing sites by 2004

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Management Guidance

(This guidance is a general summary; for detailed information or advice consult the references or contacts below.)

The Plants of Najas marina can be very badly affected by cutting. The later in the season that cutting occurs the greater the effect as seeds produced by the plant early in the year, but which are not yet matured, will be lost. Even if cutting is done early in the year, seed viability is badly affected as although the plant re-grows, new parts have a shorter period in which to produce seed and this leads to far greater numbers of seeds in the re-growth being non-viable.

Najas marina has an approximate 10:1, female:male sex ratio which may also lead to populations being badly affected by cutting. Although female plants can reproduce apomictically (without reproduction) new plants produced this way are essentially clones of the old. This leaves the population much more prone to disease or environmental change than if they could change their genetics through proper reproduction. If cutting removes or damages the smaller number of male plants, the chances of sexual reproduction are reduced.

Dredging can also very badly affect Najas marina populations for various reasons. Firstly there are the obvious physical effects on the plants themselves during dredging operations. Dredging, especially deep dredging or suction dredging that removes sediment representing greater than about the last 6-10 years of deposition, will remove the entire viable seed bank for this species. Exposure of firmer sediments by removal of soft, overlying sediment will also lead to failure of seedlings to establish. Najas marina plants have a very high root : shoot mass ratio and they therefore need deep, soft sediments in which to grow. Plants grown on firm sediments in lab conditions have a very low success rate and often end up detaching from the sediment and floating away.

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References

Agami, M., Beer, S. & Waisel, Y. (1980) Growth and photosynthesis of Najas marina L. as affected by light intensity. Aquatic Botany, 9, 285-289.

Agami, M. & Waisel, Y. (1983a) The effects of temperature and photoperiod on growth of Najas marina L. Proceedings of the International Symposium of Aquatic Macrophytes, (ed. C. Den Hartog), pp 16-20. Department of Aquatic Ecology, Nijmegan.

Agami, M. & Waisel, Y. (1983b) Are roots essential for normal growth of Najas marina. Proceedings of the International Symposium of Aquatic Macrophytes, (ed. C. Den Hartog), pp 287-291. Department of Aquatic Ecology, Nijmegan.

Agami, M. & Waisel, Y (1984) Germination of Najas marina. Aquatic Botany, 19, 37-44.

Agami, M. & Waisel, Y. (1986a) The role of mallard ducks (Anas platyrhynchos) in distribution and germination of seeds of the submerged hydrophyte Najas marina. Oecologia, 68, 473-475.

Agami, M. & Waisel, Y. (1986c) The life-form of Najas marina L.: is it an annual plant. Israel Journal of Botany, 35, 39.

Agami, M. & Waisel, Y. (1986d) The morphology and physiology of turions in Najas marina L. in Israel. Aquatic Botany, 26, 371-376.

Agami, M. & Waisel, Y. (1988) The role of fish in distribution and germination of seeds of the submerged macrophytes Najas marina L. and Ruppia maritima L. Oecologia, 76, 83-88.

Barry, D. H. & Jermy, A. C. (1953) Observations on Najas marina. Transactions of the Norfolk and Norwich Naturalist Society, 17, 294-297.

Bennett, A. (1883) On Najas marina L. as a British plant. Journal of Botany, 21, 353-354.

Bennett, A. (1884) Plants new to Norfolk with notes on other species. Transactions of the Norfolk and Norwich Naturalist Society, 3, 633-636.

Bennett, A. (1909) Najas marina, L., and Chara stelligera, Bauer, as Norfolk Plants. Transactions of the Norfolk and Norwich Naturalist Society, 9, 47-50.

Bone, C. & Probert, R. (1995) Ex-situ conservation of endangered aquatic plants – seed biology studies in Najas marina, Damasonium alisma and Zostera angustifolia. Royal Botanic Gardens, Kew/English Nature Research Report. Unpublished.

Broads Authority. (1983-1995) Macrophyte survey reports. Unpublished internal reports.

Broads Authority. (1996-2000) Macrophyte survey results on database. Unpublished database of macrophyte survey results.

Campbell, D. H. (1897) A morphological study of Naias and Zannichellia. Proceedings of the California Academy of Sciences: Third Series Botany, 1, 1-61.

Forsberg, C. (1965) Sterile germination of oospores of Chara and seeds of Najas marina. Physiologia Plantarum, 18, 128-137.

Handley, R. J. & Davy, A. J. (2000) Discovery of male plants of Najas marina L. (Hydrocharitaceae) in Britain. Watsonia, 23, 331-334.

Harris, J. (2001) Survey of the aquatic plants of the Upper Thurne Broads and Rivers. Report to English Nature (Norfolk Team), 22pp.

Jackson, M. J. (1983) Aquatic macrophyte surveys of the Norfolk Broads 1977 and 1982, Report to Nature Conservancy Council, Norwich.

Kennison, G. C. B. (1983-1993) Aquatic macrophyte surveys of the Norfolk Broads, Survey Reports for years 1983 to 1992, Broads Authority, Norwich.

Kennison, G. C. B. & Prigmore, D. (1994) Aquatic macrophyte surveys of the Norfolk Broads, Survey Reports for years 1993, Broads Authority, Norwich.

Kennison, G. C. B., Dunsford, D. S. & Schutten, J. (1998) Stable or changing lakes? A classification of aquatic macrophyte assemblages from a eutrophic shallow lake system in the United Kingdom. Aquatic Conservation: Marine and Freshwater Ecosystems, 8, 669-684.

Moss, B. (1988) Ecology of Fresh Waters. Blackwell Scientific Publications, Oxford.

Preston, C. D. & Croft, J. M. (1997) Aquatic Plants in Britain and Ireland. Harley Books, Colchester.

Preston, C. D. & Croft, J. M. (1998) Britain’s changing aquatic flora, British Wildlife, 10, 18-28.

Rendle, A. B. (1899) A systematic revision of the Genus Najas. Transactions of the Linnean Society of London: Second Series Botany, 5, 379-444.

Schutten, J. & Davy, A. J. (2000) Predicting the hydraulic forces on submerged macrophytes from current velocity, biomass and morphology. Oecologia, 123, 445-452.

Schutten, J., Davy, A. J., Madgwick, F. J., Coops, H., Admiral, W., Lammens, E. H. R. R., Phillips, G. L., Perrow, M. R., Holzer, T., Howes, H. R. & Jowitt, A. J. D. (1997) Factors Affecting Water Plant Recovery, Technical Report for EC LIFE Project No. 92-93/UK/031, BARS 14c/P-89. Broads Authority/Environment Agency, Norwich.

Sculthorpe, C. D. (1967) The Biology of Aquatic Vascular Plants. Edward Arnold, London.

Shaffer-Fehre, M. (1991b) The position of Najas within the subclass Alismatidae (Monocotyledons) in the light of new evidence from seed coat structures in the Hydrocharitoideae). Botanical Journal of the Linnean Society, 107, 189-209.

Stace, C. A. (1997) New Flora of the British Isles, 2nd ed. Cambridge University Press, Cambridge.

Triest, L., (1988) A revision of the genus Najas L. (Najadaceae) in the Old World. Mémoires, Academie Royale des Sciences d’Outre-Mer, Classe des Sciences Naturelles et Médicales, new series, 22 (1), 1-172.

Triest, L. (1989) Electrophoretic polymorphism and divergence in Najas marina L. (Najadaceae): molecular markers for individuals, hybrids, cytodemes, lower taxa, ecodemes and conservation of genetic diversity. Aquatic Botany, 33, 301-380.

Triest, L. (1989) Electrophoretic polymorphism and divergence in Najas marina L. (Najadaceae): molecular markers for individuals, hybrids, cytodemes, lower taxa, ecodemes and conservation of genetic diversity. Aquatic Botany, 33, 301-380.

Van Vierssen, W. (1982) Some notes on the germination of seeds of Najas marina L. Aquatic Botany, 12, 201-203.

Walter, K. S. & Gillett, H. J. eds.(1997) 1997 IUCN Red List of Threatened Plants. The World Conservation Union.

Wigginton, M. J. comp & ed (1999) British Red Data Books. 1. Vascular plants, 3rd ed. Joint Nature Conservation Committee, Peterborough.

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