Water Chestnut (Trapa natans)

Present distribution

Scientific name:	Trapa natans L.
Common name(s):	Water Chestnut, Water Caltrope

This weed is not known to be naturalised in Victoria

Habitat:

Native to Central/ Southern Europe and parts of Asia & Africa. Invasive in eastern areas of USA & Canada (DPI NSW 2006, Tutin et al 1968, MDSG 2002), & in Australia, documented as occurring in Queensland (RSC 2006). Inhabits freshwater wetlands, lakes, ponds, sluggish reaches of rivers & fresh or slightly brackish reaches of estuaries (Hummel & Kiviat 2004), preferring nutrient-rich waters (Tutin et al 1968). In Kashmir, India it inhabits lakes & rivers to 2500m, which are under ice for 3-4 months of the year (Kaul et al 1976).

Potential distribution

Potential distribution produced from CLIMATE modelling refined by applying suitable landuse and vegetation type overlays with CMA boundaries

Map Overlays Used

Broad vegetation types
Aquatic areas including; Riparian Strip, 10m Rivers, 5m Creeks; Irrigation Canals, 3m Major, 2m Minor; Wetlands excluding permanently saline and saltworks.

Colours indicate possibility of Trapa natans infesting these areas.

In the non-coloured areas the plant is unlikely to establish as the climate, soil or landuse is not presently suitable.

map showing the potential distribution of trapa natans

Red= Very high	Orange = Medium
Yellow = High	Green = Likely

Impact

QUESTION	COMMENTS	RATING	CONFIDENCE
Social
1. Restrict human access?	It creates nearly impenetrable mats across wide areas of water (ISSG.org). Large dense surface-floating mats of Trapa natans hinder navigation interfering with boating access of waterways (Kaul et al 1976, Hummel & Kiviat 2004). High nuisance value, makes the accessibility of water ways difficult.	MH	MH
2. Reduce tourism?	Forms extensive dense surface-floating mats that hinder recreational uses (Hummel & Kiviat 2004, Kaul et al 1976). ‘When the plant occupies a site, most recreational activities such as swimming, fishing from the shoreline, and the use of small boats are eliminated or severely impeded (Pemberton 2002)’. Major impact on recreation with weeds obvious to most visitors, would significantly reduce visitor numbers in areas of high infestation.	H	MH
3. Injurious to people?	The barbed spine-tips on the nuts can break off in the skin causing infection (Hummel & Kiviat 2004) and painful injuries to swimmers can occur when sharp nut hulls are stepped on, even penetrating shoes. Nuts could be present at all times of year. It has also been implicated in 3 drownings in the Hudson River in 2001, with evidence consistent with the victims being swept in to T. natans bed and then drowning after becoming severely entangled (Bonopartis 2001 in Hummel & Kiviat 2004). Large spines, and the potential for more serious implications.	H	M
4. Damage to cultural sites?	As a floating aquatic species (Cattaneo et al 1998), it is unlikely to cause damage to cultural sites or infrastructure.	L	M
Abiotic
5. Impact flow?	The heavy cover in Trapa beds causes reduced water movement (Strayer et al 2003). Being a free floating aquatic (Cattaneo et al 1998) it is likely to have only a minor impact on surface water flow.	ML	M
6. Impact water quality?	Can cover the water surface, intercepting up to 95% of sunlight, shading and suppressing submergent and other floating macrophytes (Pemberton 2002, Cattaneo et al 1998, Hummel & Kiviat 2004). In Italy Trapa natans is harvested to reduce eutrophication of lakes (Cattaneo et al 1998). Its stems and roots consume oxygen from the water and beneath T. natans beds it can become hypoxic or completely anoxic (Caraco & Cole 2002 in Strayer et al 2003). High effects on dissolved oxygen and light with the potential to cause eutrophication.	H	M
7. Increase soil erosion?	Due to the aquatic floating habit of T. natans, no information was found to suggest it increases soil erosion.	L	M
8. Reduce biomass?	The biomass of a community is likely to increase due to Trapa natans forming very dense large floating mats to 3m thick, comprising up to 1000g of dry matter / m²(Strayer et al 2003, Cattaneo et al 1998).	L	M
9. Change fire regime?	Trapa natans would have no impact on the fire regime as it is a permanent aquatic species.	L	MH
Community Habitat
10. Impact on composition (a) high value EVC	Covers the water surface, shading and suppressing submergent and floating macrophytes (Pemberton 2002, Cattaneo et al 1998, Hummel & Kiviat 2004). A fierce competitor in shallow water, out competing native species (ISSG 2005) and documented as replacing several indigenous submergent species in the Hudson River, USA (Hummel & Kiviat 2004). ‘…the plant community became a virtual monoculture of Trapa (Groth et al 1996)’.	H	M
(b) medium value EVC	Aquatic species. All Victorian water bodies considered to comprise high value EVCs only (Weiss pers. com).	L	M
(c) low value EVC	Aquatic species. All Victorian water bodies considered to comprise high value EVCs only (Weiss pers. com).	L	M
11. Impact on structure?	T. natans is capable of completely covering the water surface, intercepting up to 95% of sunlight and causing shading out and suppression of both submergent and other floating macrophytes (Pemberton 2002, Cattaneo et al 1998, Hummel & Kiviat 2004). ‘…the plant community became a virtual monoculture of Trapa (Groth et al 1996)’. Major effect on all layers of vegetation.	H	MH
12. Effect on threatened flora?	T. natans is a fierce competitor in shallow water, out competing native species (ISSG 2005) and documented as having replaced several indigenous submergent species in the Hudson River, USA (Hummel & Kiviat 2004). Likely to have a significant impact on threatened aquatic flora, however no information specific to threatened species was found documented.	MH	L
Fauna
13. Effect on threatened fauna?	There is conflicting information within the literature, but it does indicate that T. natans has both positive and negative impacts on fauna. Displacement of submerged macrophytes by T. natans is believed to cause the loss of many fauna species and their replacement by more tolerant, common species (Hummel & Kiviat 2004). The dominance of T. natans can significantly alter the composition of macro-invertebrate assemblages and has been found to support lower numbers of macro-invertebrates per m²of leaf area compared with native species (Feldman 2001), resulting in a subsequent reduced food source for waterfowl and fish (Cattaneo et al 1998). Low dissolved oxygen levels under T. natans beds also negatively affects fish, leading to low species diversity (Hummel & Kiviat 2004). The impact of T. natans specifically on threatened fauna was not found documented.	MH	L
14. Effect on non-threatened fauna?	Displacement of submerged macrophytes by T. natans is believed to cause the loss of many fauna species and their replacement by more tolerant, common species (Hummel & Kiviat 2004). The dominance of T. natans can significantly alter the composition of macro-invertebrate assemblages and has been found to support much lower numbers of macro-invertebrates per m²of leaf area compared with native species Feldman (2001), resulting in a subsequent reduced food source for waterfowl and fish (Cattaneo et al 1998). Low dissolved oxygen levels under T. natans beds also negatively affects fish, leading to low species diversity (Hummel & Kiviat 2004). Reduction in habit, leading to reduction in numbers of individuals.	MH	M
15. Benefits fauna?	The extensive literature indicates that T. natans has both positive and negative impacts on fauna. Studies indicate that T. natans can support substantial macro-invertebrate communities, fish use the edge of beds for foraging, birds forage on the top of beds and several rodent species eat the seeds (Hummel & Kiviat 2004). In India the greylag goose is known to consume the seeds of T. natans (Shah et al 1983). While no information exists on the benefit to local indigenous fauna, it is likely T. natans would provide some assistance in food and shelter to similar desirable species locally.	MH	M
16. Injurious to fauna?	Documented as causing the entanglement of an osprey, which presumably occurred when it dove in to catch prey (Connor 1978 in Hummel & Kiviat 2004). Injuries to humans can occur when barbed spine-tips on the nuts break off in the skin causing infection or when the sharp nut hulls are stepped on, which have the ability to penetrate shoes (Hummel & Kiviat 2004). It is possible that similar injuries could affect fauna that utilise aquatic habitats, however, no information was found documented.	M	ML
Pest Animal
17. Food source to pests?	The nuts of T natans are documented as a food source of the Norway rat (Rattus norvegicus) and the vegetative material is consumed by white tailed deer (Odocoileus virginianus) (Hummel & Kiviat 2004). Local pest deer and rodent species may also consume this species.	ML	ML
18. Provides harbour?	In the USA it is known to provide harbour for introduced common carp (Cyprinus carpio) (Hummel & Kiviat 2004), which is also a pest species in Australian aquatic systems. Provides harbour for minor pest species.	ML	MH
Agriculture
19. Impact yield?	Not found documented as a weed of agriculture.	L	M
20. Impact quality?	Not found documented as a weed of agriculture.	L	M
21. Affect land value?	Not found documented as a weed of agriculture.	L	M
22. Change land use?	Not found documented as a weed of agriculture.	L	M
23. Increase harvest costs?	Although, it is not documented as a weed of agriculture, it is possible that livestock accessing waterways could be injured if they step on the nuts with their barbed spine-tips and sharp hulls, which are documented as causing painful injuries in humans and as being able to penetrate shoes (Hummel & Kiviat 2004). This could lead to injuries requiring treatment, increasing overall production, and therefore harvest costs.	M	L
24. Disease host/vector?	A host of Fasciolopsis buski, the giant intestinal fluke, in Asia, which can infect humans and pigs after the consumption of T. natans nuts (Wallace 1936, Hummel & Kiviat 2004). However, it is not documented as a parasite of agricultural animals in Australia.	L	M

Invasive

QUESTION	COMMENTS	RATING	CONFIDENCE
Establishment
1. Germination requirements?	Seeds begin to germinate within a month of water temperature rising above 12^oC in Spring (Hummel & Kiviat 2004). Natural seasonal disturbances are required for germination.	MH	MH
2. Establishment requirements?	It cannot grow in shade (PFAF 2004). ‘Water chestnut requires full sun, sluggish, nutrient-rich [prefers], fresh waters, and soft substrate (Hummel & Kiviat 2004)’. Requires more specific requirements to establish.	ML	M
3. How much disturbance is required?	Establishes in minor disturbed (prefers nutrient rich) aquatic systems, such as lakes, wetlands, and rivers (Hummel & Kiviat 2004, Cattaneo et al 1998, Kaul et al 1976).	MH	M
Growth/Competitive
4. Life form?	Floating–leaved aquatic (Cattaneo et al 1998), for entire lifespan.	H	H
5. Allelopathic properties?	From the extensive literature no information was found documented to suggest T. natans possesses any allelopathic properties.	L	M
6. Tolerates herb pressure?	Grass carp and some beetle species are known to consume and cause significant damage to water chestnut foliage, however, it is also documented that ‘100% leaf damage is necessary to significantly reduce the number or mass of water chestnut fruits (Hummel & Kiviat 2004)’. This is a good indication that T. natans is capable of seed production under moderate herbivory pressure.	MH	MH
7. Normal growth rate?	‘Once the primary stem has developed and produced the first floating leaves secondary offshoots begin to develop at a rapid rate. The rapid vegetation of water chestnut in low-density conditions contributes greatly to its success as an aquatic invader (MDSG 2002)’. T. natans is a fierce competitor in shallow water and out competes native aquatic species (ISSG 2005). Rapid growth rate.	H	M
8. Stress tolerance to frost, drought, w/logg, sal. etc?	Grows in slightly brackish reaches of estuaries (Hummel & Kiviat 2004), and found it to have higher cell membrane stability compared to other species, indicating salinity tolerance (Hoque & Arima 2000). It is stated that in the USA adult plants are killed by frost in Autumn (Hummel & Kiviat 2004), but also that it is ‘hardy in all but the coldest parts of Britain (PFAF 2004)’ and grows in lakes that are under ice for 4 months of the year (Kaul et al 1976), therefore it is likely to tolerate Victorian frosts. In addition, its short lifecycle is completed before frosts arrive. As an aquatic plant it is tolerant of water logging and can also grow in variable depths of water up to 5m (MDSG 2002), enabling it to endure fluctuations. It is also likely to tolerate drought, as larger lakes and rivers, would not totally dry up under normal drought conditions, allowing the adult plants or at least the propagules to survive. As an aquatic it does not occur in a habitat significantly affected by fire. Displays tolerance to frost, salinity, water logging & drought.	MH	M
Reproduction
9. Reproductive system	Trapa natans reproduces by seeds and stolons (Cattaneo et al 1998, Kaul et al 1976). Reproduces both sexually and vegetatively.	H	H
10. Number of propagules produced?	Each water chestnut seed can potentially produce 15 to 20 rosettes. Each rosette can generate up to 20 seeds (MDSG 2002). Potentially, each plant therefore has the capacity to produce up to a maximum of around 400 seeds in a season.	ML	M
11. Propagule longevity?	As long as they are kept moist, seeds are capable of remaining dormant in bottom sediments for up to 10 years (Hummel & Kiviat 2004). ‘…individual seeds may remain viable for up to 12 years… (Winne 1935 in Madsen 1993)’. The literature suggests seeds have the potential to remain viable for 10 years or more, but a medium rating has been assigned due to a lack of information on the relative viability of dormant seeds.	M	M
12. Reproductive period?	‘…T. natans is an annual reproducing by seeds that germinate in late April, and which completely disappears in November (Cattaneo et al 1998)’. Mature plant produces viable propagules for one 1 year.	L	H
13. Time to reproductive maturity?	‘…T. natans is an annual reproducing by seeds that germinate in late April, and which completely disappears in November (Cattaneo et al 1998)’. Reaches maturity and produces viable propagules in under a year.	H	H
Dispersal
14. Number of mechanisms?	The barbed spines of the nut enable them to cling to moving objects, including the plumage of large water birds, mammal fur, human clothing, nets, wooden boats, construction equipment, and other vehicles (Hummel & Kiviat 2004). Lateral dispersal can occur when plants are uprooted and float downstream (MDSG 2002). Propagules spread by water and attachment.	MH	MH
15. How far do they disperse?	Due to the production of few seeds, and limited dispersal because the large heavy nuts often just sink, it is likely that very few to no propagules would disperse to one kilometre. However, the ease of attachment to moving objects and the flowing water habitat in which the plant can live increases the chances that a significant number of seeds will disperse 20-200m.	ML	MH

References

Bonopartis N 2001, ‘Details few in Esopus drownings’, Poughkeepsie Journal (25 July): 1B

Caraco NF & Cole JJ 2002, ‘Contrasting impacts of a native and alien microphyte on dissolved oxygen in a large river’, Ecological Applications, vol. 12, pp. 1496-1509.

Cattaneo A, Galanti G, Gentinetta S & Romo S 1998, ‘Epiphytic algae and macro invertebrates on submerged and floating-leaved macrophytes in an Italian lake’, Freshwater Biology

Feldman RS 2001, ‘Taxonomic and size structures of phytophilous macro invertebrate communities in Villisneria and Trapa beds of the Hudson River, New York’, Hydrobiologica, vol. 452, no. 1-3, pp. 233-245.

Groth AT, Lovett-Doust L, & Lovett-Doust J 1996, ‘Population density and module demography in Trapa natans (Trapceae), an annual, clonal aquatic macrophyte’, American Journal of Botany, vol. 83, no. 11, 1406-1415.

Hoque MA & Arima S 2000, ‘Evaluation of salt damage through cell membrane stability monitored by electrolyte leakage in water chestnut (Trapa sp.)’, Bulletin of the Faculty of Agriculture, Faculty of Agriculture, Saga University, Saga, Japan, vol. 85, pp. 141-146.

Hummel M & Kiviat E 2002, ‘Review of world literature on Water chestnut with implications for management in North America’, Journal of Aquatic Plant Management, vol. 42, pp. 17-28.

Invasive Species Specialist Group (ISSG) 2005, Trapa natans (aquatic plant), Global Invasive Species Database, viewed 26/3/2007, http://www.issg.org/database/species/ecology.asp?si=567&fr=1&sts=sss

Kaul V, Zutshi P & Vass KK 1976, ‘Aquatic weeds in Kashmir’, in Aquatic weeds in South East Asia: Proceedings of the Regional Seminar on Noxious Aquatic Vegetation, New Delhi, 1973, eds. C.K. Varshny and J Rzoska.

Maryland Sea Grant College (MDSG) 2002, ‘Invasive Species in the Chesapeake Watershed-Water Chestnut (Trapa natans L.)’. For: Chesapeake Bay Invasive Species Workshop, Maryland, 2002, viewed: 26/3/2007, http://www.mdsg.umd.edu/issues/restoration/non-natives/workshop/water_chestnut.html

NSW Department of Primary Industries (NSW DPI) 2007, ‘Weed ‘alerts’- Water Caltrop’, NSW DPI, Agriculture, Weeds management, viewed: 16/5/2007,
http://www.agric.nsw.gov.au/reader/weed-alerts

Pemberton RW, ‘Water Chestnut- Invasive plants of the Eastern United States’ (internet version). In: Biological control of invasive plants in the eastern United States, Van Driesche R, et al, USDA Forest Service Publication FHTET-2002-04, viewed: 27/2/2007, http://www.invasive.org/eastern/biocontrol/3WaterChestnut.html

Plants for a Future (PFAF) 2004, ‘Trapa natans L.’, Plants for a Future Database, viewed: 4/4/2007, http://www.pfaf.org/database/plants.php?Trapa+natans

Redland Shire Council (RSC) 2006, Redland Shire Council Planning Scheme (declared weeds list & shire map), RSC, Queensland, viewed: 2/5/2007,
http://pdonline.redland.qld.gov.au/masterplan/enquirer/publishR.aspx?page=eplan

Shah MG, Qadri MY & Inayat-Ullah M 1983, ‘Food of the greylag goose, Anser anser Linnaeus (Anseriiformes: Anatidae), Journal of the Indian institute of Science, vol. 64, no. 12, pp. 179-188.

Strayer DL, Lutz C, Heather M, Munger K & Shaw WH 2003, ‘invertebrate communities associated with a native (Vallisneria americana) and an alien (Trapa natans) macrophyte in a large river, Freshwater Biology, vol. 48, pp. 1938-1949.

Tutin TG, Heywood VH, Burges NA, Moore DM, Valentine DH, Walters SM & Webb DA (eds.) 1968, ‘Flora Europaea: Volume 2-Rosaceae to Umbelliferae’,
University Press, Cambridge.

Wallace FG 1936, ‘A new intermediate host of Fasciolopsis buski (Lankester) (Trematoda: Fasciolidae)’, Lingnan Science Journal, vol. 15, no. 1, pp. 125-126.

Winne W 1935, ‘A study of the Water chestnut, Trapa natans with a view to its control in the Mohawk River’. Cornell University, Ithaca, New York.

Global present distribution data references

Den virtuella floran (DVF) 2007, Naturhistoriska riksmuseet, viewed 2/5/2007, http://linnaeus.nrm.se/flora/

Global Biodiversity Information Facility (GBIF) 2007, Global biodiversity information facility: Prototype data portal, viewed; 2/5/2007, http://newportal.gbif.org/welcome.htm

Redland Shire Council (RSC) 2006, Redland Shire Council Planning Scheme (declared weeds list & shire map), RSC, Queensland, viewed: 2/5/2007,
http://pdonline.redland.qld.gov.au/masterplan/enquirer/publishR.aspx?page=eplan

Strayer DL, Lutz C, Heather M, Munger K & Shaw WH 2003, ‘invertebrate communities associated with a native (Vallisneria americana) and an alien (Trapa natans) macrophyte in a large river, Freshwater Biology, vol. 48, pp. 1938-1949.

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