Title: Egeria densa Planch.

Scientific Name:

Egeria densa Planch.

Common Name:

dense waterweed, egeria, leafy elodea



Source & more images (via ALA)

Habitat : Can invade; freshwater wetlands, lakes, slow moving streams, dams and channels (Weber, 2003).

Distribution:



Original source via CABI


Invasiveness Assessment

ESTABLISHMENT


1. Germination requirements? In Australia reproduction is by vegetative means due to the lack of female plants. Broken stem fragments over winter then commence growth in spring (Parsons & Cuthbertson, 2001).

2. Establishment requirements? The species prefers slow moving water, however it has a low light requirement, able to grow to depths of 7m, and can tolerate a range of nutrient levels with this only effecting growth rates not establishment of persistence (Parsons & Cuthbertson, 2001).

3. How much disturbance is required? Able to invade freshwater wetlands, lakes and slow moving streams (Weber, 2003).

GROWTH / COMPETITIVE


4. Life form? Attached submerged aquatic species (Parsons & Cuthbertson, 2001).

5. Allelopathic properties? Reported not to have allelopathic effects on blue-green algae (Nakai et al, 1999).

6. Tolerates herb pressure? Successful bio-control of this species has been reported in New Zealand after the stocking of grass carp (Ctenopharyngodon idella) (Tanner, Wells & Mitchell 1990). However no such program is reported in Australia and no species present in Australia are reported to eat significant quantities of this plant (Parsons & Cuthbertson, 2001). Cutting encourages fragmentation and spread (Weber, 2003).

7. Normal growth rate? A fast growing aquatic species (Weber, 2003). Reported to displace native ribbon weeds on the Hawkesbury-Nepean river (Roberts, Church & Cummins, 1999). In New Zealand the only other exotic species to out compete it is Hydrilla verticillata, however egeria is more competitive under certain conditions including a sandy substrate and lower nutrient levels (Hofstra et al, 1999; Mony et al, 2006).

8. Stress tolerance to frost, drought, w/logg, sal. etc? Submerged aquatic species (Weber, 2003). Therefore tolerant of waterlogging. Only reported in fresh water (Weber, 2003). Therefore susceptible to salinity. Aquatic species therefore protected from fire. Can survive short periods under ice, but does not survive long periods of near freezing temperatures (DiTomas & Healy, 2003).

REPRODUCTION


9. Reproductive system? Is a dioecious species, requiring female and male individuals (Weber, 2003). Female plants are reported not to occur in Australia, therefore the species is restricted to vegetative growth (Parsons & Cuthbertson, 2001).

10. Number of propagules produced? Vegetative propagules need to be double node, which are regularly spaces at intervals of every 6-12th node (DiTomas & Healy, 2003). Stems can be 5m or more, long, with nodes varying in size to as little as 2mm (Parsons & Cuthbertson, 2001). Therefore a single stem could be broken into more than a hundred propagules.

11. Propagule longevity? Reproduction restricted to vegetative in Australia (Parsons & Cuthbertson, 2001).

12. Reproductive period? Can form monocultures (Coffey & Clayton, 1988).

13. Time to reproductive maturity? Fast growing, vegetatively reproductive species (Weber, 2003). Therefore could produce vegetative propagules within first year.

DISPERSAL


14. Number of mechanisms? Propagules may be dispersed by water, waterfowl or human actions (DiTomas & Healy, 2003).

15. How far do they disperse? In flooding situations water can disperse propagules more than 1km. Large waterfowl such as swans can travel distances greater than 1km.


Impact Assessment

RECREATION


1. Restrict human access? Can interfere with boating, and could cause drowning due to entanglement (Champion, 1995). Therefore a high nuisance impeding people and vehicles.

2. Reduce tourism? Can interfere with activities such as fishing, swing and boating (Parsons & Cuthbertson, 2001). However evidence of major impact and visitor complaints not reported.

3. Injurious to people? Poses the risk of drowning, due to entanglement (Champion, 1995). This risk would be greatest at the highest biomass levels reported in February to March, when the species forms a thick mat of intertwining stems below the surface (Parsons & Cuthbertson, 2001).

4. Damage to cultural sites? Can interfere with infrastructure, including, irrigation works, hydro-electric outputs and water supplies (Parsons & Cuthbertson, 2001).

ABIOTIC


5. Impact flow? An attached submerged species preferring slow moving water, reported to seriously retard flow (Parsons & Cuthbertson, 2001).

6. Impact water quality? Can help to stabilise shallow systems, by reducing wave action and stabilising sediment. However when the species builds up to high biomass levels, the system can collapse. Benthic anoxia leads to death of large proportions of the egeria. This can cause the wetland to flip and become turbid and dominated by phytoplankton (Champion, 2002).

7. Increase soil erosion? Can act as a semi-permeable dam, slowing flow and increasing stream depth (Champion & Tanner, 2000). However during times of high flow can cause flooding and therefore increase the chance of erosion (DiTomas & Healy, 2003).

8. Reduce biomass? This species would either be a direct replacement or potentially increases biomass, as can from dense monospecfic stands to depths of 5m (Coffey & Clayton, 1988).

9. Change fire regime? Aquatic species; not present in vegetation exposed to fire.

COMMUNITY HABITAT


10(a) Impact on composition of high value EVC? EVC= Shallow Freshwater Marsh (E); CMA= Corangamite; Bioreg= Otway Plain; VH CLIMATE potential. Can form monospecific stands (Coffey & Clayton, 1988). Reported displacing native submerged macrophytes (Roberts, Church & Cummins, 1999).

10(b) Impact on medium value EVC? Aquatic species. All Victorian water bodies considered to comprise high value EVCs only (Weiss pers. com).

10(c) Impact on low value EVC? Aquatic species. All Victorian water bodies considered to comprise high value EVCs only (Weiss pers. com).

11. Impact on structure? Can form monosepcific stands (Coffey & Clayton, 1988). Reported displacing native submerged macrophytes (Roberts, Church & Cummins, 1999).

12. Effect on threatened flora? Has been reported to displace native submerged macrophytes (Roberts, Church & Cummins, 1999). However no specific information on threatened species.

FAUNA


13. Effect on threatened fauna? Reported to harbour different fish assemblages than those of native submerged macrophytes (Growns et al, 2003). However no specific information on impact on threatened species.

14. Effect on non-threatened fauna? Reported to harbour different fish assemblages than those of native submerged macrophytes (Growns et al, 2003). Therefore decrease in populations of some species with an increase in population of other species.

15. Benefits fauna? Provides a major food source for black swan (Cygnus atratus) (Champion, 2002). Fish assemblages and invertebrate species are reported living amongst it, and can act as protection from predators (Duggan et al ,2001; Growns et al, 2003). Therefore it provides an abundant food source for at least one species and it creates a habitat and shelters various species. However unknown specifically for native species.

16. Injurious to fauna? No evidence of this reported. However it is reported to have potential to drown people through entanglement, it may therefore be able to drown animal species.

PEST ANIMAL


17. Food source to pests? There are exotic fish species reported to eat significant quantities of the species that they could be used for biocontrol measures, However they are not reported in Australia (Parsons & Cuthbertson, 2001).

18. Provides harbor? Provides habitat for a fish assemblage (Growns et al, 2003). Therefore could provide harbour for exotic fish species.

AGRICULTURE


19. Impact yield? Aquatic species, no evidence of this reported.

20. Impact quality? Aquatic species, no evidence of this reported.

21. Affect land values? Aquatic species, no evidence of this reported.

22. Change land use? Aquatic species, no evidence of this reported.

23. Increase harvest costs? Can interfere with irrigation activities and block pumps, therefore increased maintenance costs (Parsons & Cuthbertson, 2001).

24. Disease host/vector? Aquatic species, no evidence of this reported.




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Assessment ratings originally made by the Victorian Department of Primary Industries.
The entry of this assessment was made possible through the generous support of an anonymous donor.






Attachments:
Egeria densa potential distribution.doc
Egeria densa present distribution.doc
ergaria via ala.JPG
distribution_map (25).png
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referenced by (3)
wra1008: Common Names - L (via leafy elodea)wra999: Common Name - E (via Egeria)wra998: Common Name - D (via Dense Waterweed)
Article: wra5996 (permalink)
Categories: :wra:e, :wra:inv1, :wra:invmh, :wra:inv2, :wra:invh, :wra:inv3, :wra:inv4, :wra:inv5, :wra:invl, :wra:inv6, :wra:inv7, :wra:inv8, :wra:inv9, :wra:inv10, :wra:invml, :wra:inv11, :wra:inv12, :wra:inv13, :wra:inv14, :wra:inv15, :wra:imp1, :wra:impmh, :wra:imp2, :wra:imp3, :wra:imp4, :wra:imp5, :wra:imph, :wra:imp6, :wra:imp7, :wra:impml, :wra:imp8, :wra:impl, :wra:imp9, :wra:imp10a, :wra:imp10b, :wra:imp10c, :wra:imp11, :wra:imp12, :wra:imp13, :wra:imp14, :wra:imp15, :wra:imp16, :wra:impm, :wra:imp17, :wra:imp18, :wra:imp19, :wra:imp20, :wra:imp21, :wra:imp22, :wra:imp23, :wra:imp24
Date: 17 December 2009; 12:00:45 PM AEDT

Author Name: Michelle Heitch
Author ID: heitchm