Water soldier (Stratiotes aloides)

Present distribution

Scientific name:	Stratiotes aloides L.
Common name(s):	Water soldier, crab’s claw

This weed is not known to be naturalised in Victoria

Habitat:

Occurs in peaty oxbow lakes (Loeb et al. 2008), ponds, ditches, reed zones of rivers and larger lakes (Nielson, Borum 2008), light- and oxygen-limited conditions in shallow lentic water bodies (Glińska-Lewczuk 2009), shallow stagnant water, mainly eu- and mesotrophic, with the substratum composed of a thick layer of mud and organic deposits, avoids extremely high ammonium concentrations (Strzałek, Koperski 2009). “When present in small water bodies, the species is often dominant and completely covers the water surface…seems less able to establish on larger lakes” (Nielson, Borum 2008). “Needs moderately high nutrient concentrations… absent in oligotrophic waters” (Mulderij et al. 2005).

Potential distribution

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

Map Overlays Used

Land Use:
Water

Ecological Vegetation Divisions
Freshwater wetland (permanent); freshwater wetland (ephemeral)

Colours indicate possibility of Stratiotes aloides 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 stratiotes aloides

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

Impact

QUESTION	COMMENTS	RATING	CONFIDENCE
Social
1. Restrict human access?	“When present in small water bodies, the species is often dominant and completely covers the water surface with a dense and highly productive stand of up to 50 cm high floating rosettes” (Nielson & Borum 2008). Major impediment to access waterways or machinery. Significant works required to provide reasonable access, tracks closed or impassable.	H	H
2. Reduce tourism?	“When present in small water bodies, the species is often dominant and completely covers the water surface with a dense and highly productive stand of up to 50 cm high floating rosettes” (Nielson & Borum 2008). Major impact on recreation. Weeds obvious to most visitors, with visitor response complaints and major reduction in visitors.	H	H
3. Injurious to people?	No reference to injurious properties in the literature (Glińska-Lewczuk 2009; Nielson & Borum 2008; Linhart 1999) No effect, no prickles, no injuries.	L	H
4. Damage to cultural sites?	“When present in small water bodies, the species is often dominant and completely covers the water surface with a dense and highly productive stand of up to 50 cm high floating rosettes” (Nielson & Borum 2008) Moderate visual effect.	ML	H
Abiotic
5. Impact flow?	As the “water surface often becomes completely covered” by S. aloides (den Broek & Beltman 2006) and “there are two forms of Stratiotes aloides, of which the first is entirely submerged, and never flowers, and the second produces erect, emerged, flowering shoots in summer” (Erixon 1979) It is likely to have serious impacts both to surface and subsurface water flow.	H	H
6. Impact water quality?	“A dense vegetation cover has important consequences for the entire ecosystem through modification of chemical and physical parameters of water” (Glińska-Lewczuk 2009). It “is thought to strongly affect phyto- and zooplankton composition in adjacent open water”. “Species overwintering green… may immobilise nutrients for long periods”. “In some lakes the detritus of Stratiotes forms a thick layer on bottom sediments”. “Stratiotes detritus can store part of N and P after the growing season and gradually release these nutrients back into the water column” (Strzałek & Koperski 2009). “Markedly changes the in situ concentrations of K+, Na+ and Ca+. Also lake water phosphorus and nitrogen levels decrease, suggesting that the dominant Stratiotes might withdraw nutrients not only from the sediment but also from the surrounding water” (Mulderij et al. 2005) High effects in either dissolved 02 and/or light; causing eutrophication.	H	H
7. Increase soil erosion?	“Free floating amphibious plant” (Nielson & Borum 2008). “There are two forms of Stratiotes aloides, of which the first is entirely submerged, and never flowers, and the second produces erect, emerged, flowering shoots in summer” (Erixon 1979) Aquatic species therefore a low probability of large scale soil movement.	L	H
8. Reduce biomass?	“The water soldier grows quickly and its net production is very high… Such considerable production and biomass suggest high demands for nutrients” (Strzałek & Koperski 2009) Biomass may increase.	L	H
9. Change fire regime?	“Free floating amphibious plant” (Nielson & Borum 2008). “There are two forms of Stratiotes aloides, of which the first is entirely submerged, and never flowers, and the second produces erect, emerged, flowering shoots in summer” (Erixon 1979). Aquatic; Small or negligible effect on fire risk.	L	H
Community Habitat
10. Impact on composition (a) high value EVC	EVC = Freshwater meadow (E); CMA = Glenelg Hopkins; Bioregion = Bridgewater; VH CLIMATE potential. Monoculture within a specific layer.	H	H
(b) medium value EVC	Aquatic weed. All water bodies in Victoria are given a high value EVC.	L	H
(c) low value EVC	Aquatic weed. All water bodies in Victoria are given a high value EVC.	L	H
11. Impact on structure?	“When present in small water bodies, the species is often dominant and completely covers the water surface with a dense and highly productive stand of up to 50 cm high floating rosettes… seems less able to establish on larger lakes” (Nielson & Borum 2008). “The water table was almost completely overgrown by a monoculture of water soldier (Stratiotes aloides)” (Linhart 1999). Major effects on all layers, forms monoculture; no other strata/layers present.	H	H
12. Effect on threatened flora?	As S. aloides has not yet been recorded in Victoria (ANH 2009), it is not known to impact on Bioregional Priority 1A or VROT spp. However, Johnson (undated) warns that it has potential to become weedy in Australia and “can exclude native wetland plants and destroy the habitat of fauna,” therefore; this species has potential to affect threatened species.	MH	L
Fauna
13. Effect on threatened fauna?	As S. aloides has not yet been recorded in Victoria (ANH 2009), it is not known to impact on Bioregional Priority 1A or VROT spp. However, Johnson (undated) warns that it has potential to become weedy in Australia and “can exclude native wetland plants and destroy the habitat of fauna,” therefore; this species has potential to affect threatened species.	MH	L
14. Effect on non-threatened fauna?	Johnson (undated) warns that it “can exclude native wetland plants and destroy the habitat of fauna.” Indeed it substantially changes water quality (Strzałek & Koperski 2009; Mulderij et al. 2005) and forms a monoculture (Linhart 1999). Habitat changed dramatically, leading to the possible extinction (extirpation) of non-threatened fauna.	H	H
15. Benefits fauna?	Has been used as fodder for livestock in Finland (Erixon 1979). Stratiotes beds determine the abundance and diversity of planktonic crustaceans in a studied environment and seemed to provide a daytime refuge for Ceriodaphnia and older stages of Cyclopoida. Stratiotes stands are known as habitats of an endangered dragonfly Aeshna viridis Eversm. and other phytophylous and mining invertebrates… The water soldier bed appears to determine zooplankton abundance and biodiversity in lake Bużysko.” (Strzałek & Koperski 2009). “A plant community dominated by Stratiotes is usually associated with a species-rich macrofauna” (in its native environment) (Erixon 1979). May provide some assistance in either food or shelter to desirable species	MH	H
16. Injurious to fauna?	Not reference to injurious properties in the literature (Glińska-Lewczuk 2009; Nielson & Borum 2008; Linhart 1999). No effect	L	H
Pest Animal
17. Food source to pests?	Not eaten by fish “due primarily to their physical properties” (Prejs 1984). Likely to provide minimal food for pest animals.	L	H
18. Provides harbour?	Covers an oxbow lake in Bużysko, in which crucian carp inhabit (Strzałek & Koperski 2009) and Cyprinus carpio and Stratiotes aloides have been recorded to occur in the same waterway (De Beelde et al. 2008). Capacity to provide harbour for noxious pests.	H	H
Agriculture
19. Impact yield?	Not listed as a weed of agriculture (Randall 2007), however, as it is “often dominant and completely covers the water surface with a dense and highly productive stand of up to 50 cm high floating rosettes” (Nielson & Borum 2008) and has substantial impacts on water quality (Strzałek & Koperski 2009; Mulderij et al. 2005), it may impact on aquaculture yields. However, this is, as yet, unknown.	M	L
20. Impact quality?	Not listed as a weed of agriculture (Randall 2007), however, as it is “often dominant and completely covers the water surface with a dense and highly productive stand of up to 50 cm high floating rosettes” (Nielson & Borum 2008) and has substantial impacts on water quality (Strzałek & Koperski 2009; Mulderij et al. 2005), it may impact on aquaculture quality of yield. However, this is, as yet, unknown.	M	L
21. Affect land value?	Not listed as a weed of agriculture (Randall 2007), however, as it is “often dominant and completely covers the water surface with a dense and highly productive stand of up to 50 cm high floating rosettes” (Nielson, Borum 2008) and has substantial impacts on water quality (Strzałek & Koperski 2009; Mulderij et al. 2005), it may affect land value. However, this is, as yet, unknown.	M	L
22. Change land use?	Not listed as a weed of agriculture (Randall 2007), however, as it is “often dominant and completely covers the water surface with a dense and highly productive stand of up to 50 cm high floating rosettes” (Nielson & Borum 2008) and has substantial impacts on water quality (Strzałek & Koperski 2009; Mulderij et al. 2005), it may cause a change of land use. However, this is, as yet, unknown.	M	L
23. Increase harvest costs?	Not listed as a weed of agriculture (Randall 2007), however, as it is “often dominant and completely covers the water surface with a dense and highly productive stand of up to 50 cm high floating rosettes” (Nielson & Borum 2008) and has substantial impacts on water quality (Strzałek & Koperski 2009; Mulderij et al. 2005), it may increase aquaculture harvest costs. However, this is, as yet, unknown.	M	L
24. Disease host/vector?	Not listed as a disease host or vector (Strzałek & Koperski 2009; Mulderij et al. 2005). Little or no host.	L	M

Invasive

QUESTION	COMMENTS	RATING	CONFIDENCE
Establishment
1. Germination requirements?	“Stratiotes aloides L. seeds need neither light, nor oxygen, no vernalisation to germinate but the germlings need light and oxygen for further development. Germination, however, is delayed strongly by the mechanical resistance of the seed coat” (Smolders et al. 1995b). Opportunistic germinator, can germinate or strike/ set root at any time whenever water is available.	H	H
2. Establishment requirements?	“Seedlings only developed under aerobic conditions with sufficient light. Under hypoxic conditions or in the dark all seedlings died within two weeks after germination.” (Smolders et al. 1995b). Requires more specific requirements to establish (e.g. open space or bare ground with access to light and direct rainfall).	ML	H
3. How much disturbance is required?	“S. aloides usually inhabits shallow stagnant water, mainly eu- and mesotrophic, with the substratum composed of a thick layer of mud and organic deposits but the species appears to avoid extremely high ammonium concentrations” (Strzałek, Koperski 2009). “For growth and reproduction, Stratiotes needs moderately high nutrient concentrations and is, therefore, absent in oligotrophic waters” (Mulderij et al. 2005). Occurs in a “shallow, polymictic, eutrophic lake [which is] almost undisturbed by anthropogenic pressure and is close to its natural state” (Linhart 1999). Establishes in relatively intact or only minor disturbed natural ecosystems (e.g. wetlands, riparian, riverine, grasslands, open woodlands).	MH	H
Growth/Competitive
4. Life form?	“Free floating amphibious plant” (Nielson & Borum 2008). “There are two forms of Stratiotes aloides, of which the first is entirely submerged, and never flowers, and the second produces erect, emerged, flowering shoots in summer” (Erixon 1979) . Aquatic.	H	H
5. Allelopathic properties?	“After plant emergence on the water surface, algae were probably limited by light and/or allelochemicals exuded from Stratiotes” (Strzałek & Koperski 2009) . Allelopathic properties seriously affecting some plants.	MH	H
6. Tolerates herb pressure?	An “enormous infection” of mining chiromonid larvae was found to occur in S. aloides leaves; however young rosettes were not infested (Linhart 1999). Also “predation on seedlings by snails such as Planorbarius corneus (L.)” (Smolders et al. 1995b) was observed. Although S. aloides is not eaten by fish “due primarily to their physical properties” (Prejs 1984). Consumed but non-preferred or consumed but recovers quickly; capable of flowering /seed production under moderate herbivory pressure.	MH	H
7. Normal growth rate?	“The water soldier grows quickly and its net production is very high” (Strzałek & Koperski 2009) and also “shows vigorous clonal branching by means of tillers and turions” (Mulderij et al. 2005). Rapid growth rate that will exceed most other species of the same life form.	H	H
8. Stress tolerance to frost, drought, w/logg, sal. etc?	“a peaty oxbow lake, featuring Stratiotes aloides mats” (Loeb et al. 2008) “Freezing in situ is quite normal and is only lethal if the overwintering basal rosettes become frozen solid. The turions are quite frost-hardy” (Erixon 1979). “sulphate is the master variable in the decline of S. aloides in the Netherlands” – (Smolders et al. 2003) Tolerant to waterlogging and frost. Intolerant to salinity.	MH	H
Reproduction
9. Reproductive system	“dioecious perennial” and also reproduces vegetatively (Nielson & Borum 2008). Both vegetative and sexual reproduction.	H	H
10. Number of propagules produced?	“Up to 1800 seeds per 100 female plants were found” (Smolders et al. 1995b). Less than 50.	L	H
11. Propagule longevity?	“The majority of characteristic fen wetland species have a transient seed bank” (Van den Broek & Beltman 2006), therefore it may survive only one year, and however for this species the propagule longevity is unknown.	M	L
12. Reproductive period?	“Offsets that have been produced in July and August do not flower but have been counted in September as separate plants” (Smolders et al. 1995a). “New plants are produced from over-wintering turions formed by mature plants in the fall” (Nielson & Borum 2008). The reproductive period is longer than two years, and as it is a perennial, this period is assumed to be between 310 years	MH	M
13. Time to reproductive maturity?	“Offsets that have been produced in July and August do not flower but have been counted in September as separate plants” (Smolders et al. 1995a). “New plants are produced from over-wintering turions formed by mature plants in the fall” (Nielson & Borum 2008). Vegetative propagules become separate individuals, in under a year.	H	H
Dispersal
14. Number of mechanisms?	“As seed germination is enhanced after passing the digestive tract of an human being it is not unlikely that seeds are not only dispersed by animals but that germination of Stratiotes is also enhanced following endozoochoric dispersal… abundant in many ditches which points to an efficient dispersal of the species.” (Smolders et al. 1995b). Vegetative propagules “are readily distributed by wave action and currents” (Erixon 1979) Has edible fruit that is readily eaten by highly mobile animals.	H	M
15. How far do they disperse?	“As seed germination is enhanced after passing the digestive tract of an human being it is not unlikely that seeds are not only dispersed by animals but that germination of Stratiotes is also enhanced following endozoochoric dispersal… abundant in many ditches which points to an efficient dispersal of the species.” (Smolders et al. 1995b). Vegetative propagules “are readily distributed by wave action and currents” (Erixon 1979). Very likely that at least one propagule will disperse greater one kilometre.	H	H

References

De Beelde T, Hendrickx F, Bogaert D (2008) 6th European Conference on Ecological Restoration 10 September 2008. SER, Ghent, Belgium. Available at
https://www.ser.org/europe/pdf/Damvallei.pdf (verified 5 February 2009)

Erixon G (1979) Population ecology of a Stratiotes aloides L. stand in a riverside lagoon in N. Sweden. Hydrobiologia 67, 215-221.

Glińska-Lewczuk K (2009) Water quality dynamics of oxbow lakes in young glacial landscape of NE Poland in relation to their hydrological connectivity. Ecological Engineering 35, 25-37.

Johnson A (n.d) Weed Alert: Water soldier. NSW Department of Primary Industries. Available at http://www.dpi.nsw.gov.au/__data/assets/pdf_file/0006/144978/water-soldierweed-alert.pdf (verified 5 February 2009).

Jordon S (2007) Water soldiers. Department of Primary Industries and Fisheries, Queensland. Available at
http://www.dpi.qld.gov.au/cps/rde/dpi/hs.xsl/4790_7388_ENA_HTML.htm (verified 5 February 2009).

Linhart J (1999) Phytophilous macrofauna in the Stratiotes aloides vegetation of the Lake Łukie, Poland. Biologica 37, 67-76.

Loeb R, Lamers LPM, Roelofs JGM (2008) Prediction of phosphorus mobilisation in inundated floodplain soils. Environmental Pollution 156, 325-331.

Mulderij G, Mooij WM, Smolders AJP, Van Donk E (2005) Allelopathic inhibition of phytoplankton by exudates from Stratiotes aloides. Aquatic Botany 82, 284-296.

Nielson LT, Borum J (2008) Why the free floating macrophyte Stratiotes aloides mainly grows in highly CO2-supersaturated waters. Aquatic Botany 89, 379-384.

Randall R (2007) Stratiotes aloides (Hydrocharitaceae). Global Compendium of Weeds. Available at http://www.hear.org/gcw/species/stratiotes_aloides/ (verified 5 February 2009).

Smolders AJP, Lamer LPM, den Hartog, Roelofs JGM (2003) Mechanisms involved in the decline of Stratiotes aloides L. in The Netherlands: sulphate as a key variable. Hydrobiologia 506-509, 603-610.

Smolders AJP, den Hartog C, Roelofs JGM (1995a) Observations on fruiting and seed-set of Stratiotes aloides L. in The Netherlands. Aquatic Botany 51, 259-268.

Smolders AJP, den Hartog C, Roelofs JGM (1995b) Germination and seedling development in Stratiotes aloides L. Aquatic Botany 51, 269–279.

Strzałek M, Koperski P (2009) The Stratiotes aloides L. stand as a habitat in oxbow lake in Bużysko. Aquatic Botany 90, 1-6.

Van den Broek T, Beltman B (2006) Germination and seedling survival in fens undergoing succession. Plant Ecology 18(5), 221-237.

Global present distribution data references

Australian National Herbarium (ANH) (2009) Australia’s Virtual Herbarium, Australian National Herbarium, Centre for Plant Diversity and Research, Available at http://www.anbg.gov.au/avh/ (verified 5 February 2009).

Global Biodiversity Information Facility (GBIF) (2009) Global biodiversity information facility, Available at http://www.gbif.org/ (verified 5 February 2009).

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