Hydrilla verticillata: Biology and Ecology

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Hydrilla verticillata Biology and Ecology
By Carey Minteer - University of Arkansas
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Background

• Native of southeast Asia
• Introduced into the United States in 1955
• Federal noxious weed
• Since 1983 Hydrilla has been the most abundant
  submerged plant in Florida (McCann et al, 1996)

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More Background

• Plants can be monoecious or dioecious (Van
  Driesche, 2002)
• Populations in the southeastern United States are
  dioecious and entirely female.
• Plants spread through vegetative regeneration.
• Monoecious strain found in Potomac river (Steward
  et al., 1984).

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Monoecious strain

• Spreading down the Potomac river.
• Sexual reproduction can occur.
• Pollination occurs on the waters surface
• Pollen is released from free floating male
  flowers and caught by the free floating female
  flowers (Cronk and Fennessy,2001).

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Vegetative reproduction

• Subterranean tubers
• Axillary turions
• Fragments

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Subterranean Tubers

• Sometimes buried several centimeters below the
  surface.
• Can sprout new shoots even after a period of 4
  years.
• In Florida canal there are an average of 918
  turions per m-2 (Sutton, 1996).

Tim Murphy, University of Georgia, Bugwood.org
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Axillary Turions

• Turions form in the leaf axils at the ends of the
  stems.
• Turions abscise and fall into the sediment.
• Over winter and produce new growth in the spring.

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Fragmentation

• Spread from lake to lake by boats.
• Large populations found adjacent to boat ramps.
• Spreads extremely fast
• Total lake coverage can change drastically in
  just a years time.

Raghavan Charudattan, University of Florida,
Bugwood.org
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Biology

• Monocot
• Family Hydrocharitaceae
• Rooted submerged perennial
• Leaves 5-15 mm long and 2-4 mm wide
• Leaves arranged in pairs on lower nodes.
• Leaves in whorls of 3-10 on the upper nodes.

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More Biology

• Stems vary in length from a few centimeters to
  several meters.
• Three types erect, horizontal, or subterranean.
• Erect stems support branches, leaves, and flowers.

Chris Evans, River to River CWMA, Bugwood.org
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Habitat

• Sunny
• Sandy substrate
• Low levels of rock
• Grows in depths between 0.7m and 2.4m
• Has been shown to grow in depths of up to 15m.

Raghavan Charudattan, University of Florida,
Bugwood.org
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Habit

• Apical growth
• Several erect stems form at a single node of a
  horizontal stem
• Branches form a canopy
• 70 of biomass concentrated at the waters
  surface (Cronk and Fennessey, 2001).

Carey Minteer, University of Arkansas
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Distribution
http//www.eddmaps.org/distribution/subdist.cfm?su
b3028
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Effects on Native Vegetation

• Hydrilla forms lush canopies, that shades native
  vegetation.
• Alters seed banks
• Allelopathic
• Shown to inhibit the growth of Ceratophyllum
  demersum (coontail) (Schmitz et al., 1993).

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Effects on Animals

• Dense stands provide refuge for young fish.
• High survival rates leads to over population and
  stunted fish growth.
• Predator fish cannot forage as well.
• Numbers and biomass of these predatory fish
  decline.

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Effects on Human Activities

• Hydrilla reduces open water feeding and spawning
  areas of sport fish
• Clog boat motors
• Thick mats can hinder irrigation by as much as
  90 (CDFA,2000).
• Hydroelectric power is hindered by fragmentation
  of plant material

Wilfredo Robles, Mississippi State University,
Bugwood.org
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More to come

• Control of Hydrilla
• Biological, mechanical, chemical.

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Literature Cited

• California Department of Food and
  Agriculture.2000a. Hydrilla program 20.20.1,
  Program statement 2000 season, fiscal year
  200/2001. Plant Health and pest prevention
  services, Integrated pest control branch,
  Sacramento, CA.
• Cronk, J. and M. Fennessy. 2001. Wetland plants.
  Biology and Ecology. CRC Press LLC, NY.
• McCann, J.A,, Arkin, L.N., and Williams, J.P.
  1996. Nonindigenous aquatic and selected
  terrestrial species of Florida. Orlando,
  University of Florida, Center for aquatic plants
  website. http//aquat1/ifas.ufl.edu/mctitle.htm
• Schmitz, D.C., Schardt, J.D., Leslie, A.J.,
  Dray, F.A., Osborne, J.A., and Nelson, B.V.1993.
  The ecological impact and management history of
  three invasive alien aquatic plant species in
  Florida. Biological pollution The control and
  impact of Invasive exotic species. B.N. McKnight,
  Ed. Pp 173-194. Indianapolis, Indiana Academy of
  Science.
• Steward. K.K., Van, T.K., Carter,V., and
  Pieterse,A.H. 1984. Hydrilla invades Washington
  D.C. and the Potomac. American Journal of Botany
  71162-163.
• Sutton, D.L. 1996. Depletion of turions and
  tubers of Hydrilla verticillata in the North
  River canal, Florida. Aquatic Botany53121-130.