Risk Assessment for Invasive Aquatic Plants

Risk Assessment For Invasive Aquatic Plants

Reuben Keller & David Lodge

Presentation to: Invasive Plant Species Assessment Working Group Indianapolis, Nov. 30, 2004


Invasive aquatic plants in Indiana

  • Impacts
  • Sources
  • Regulations
  • Reducing the impacts

Species available through watergarden and aquarium trades Statistical risk assessment for invasive aquatic plants in the Midwest

PPT Slide

  • Invasion Process
  • Species Elsewhere
  • Introduced
  • Established
  • Invasive
  • In Pathway
  • e.g. imported for trade
  • Reproducing
  • Ecological &/or
  • Economic impacts

Invasive Aquatic Plants In Indiana

Eurasian watermilfoil (Myriophyllum spicatum) is established in 175 lakes and reservoirs, and many waterways

Curly-leafed pondweed (Potamogeton crispus)
Purple loosestrife (Lythrum salicaria) is established across IN
~$803,000 spent each year just on herbicide control
More spent on biocontrol
Value of lost opportunities (boating, fishing etc.) not estimated


Watergardening (e.g. purple loosestrife) Aquariums (e.g. Eurasian watermilfoil, curly-leafed pondweed) Landscaping, erosion control (e.g. reed canary-grass Phalaris arundinacea)

IN Regulations

Federal noxious weed list (19 species) + Lythrum

  • Azolla pinnata (mosquito fern)
  • Caulerpa taxifolia (Mediterranean clone)
  • Eichornia azurea (anchored waterhyacinth)
  • Hydrilla verticillata
  • Hygrophila polysperma (Miramar weed)
  • Ipomoea aquatica (water spinach)
  • Lagarosiphon major (Moss)
  • Limnophila sessiflora (ambulia)
  • Melaleuca quenquinervia
  • Monachoria hastata
  • Monochoria vaginalis
  • Ottelia alismoides
  • Sagittaria sagittifolia (arrowhead)
  • Salvinia auriculata (giant salvinia)
  • Salvinia biloba (giant salvinia)
  • Salvinia herzogii (giant salvinia)
  • Salvinia molesta (giant salvinia)
  • Solanum tampicense (wetland nightshade)
  • Sparganium erectum (exotic bur-reed)

Reducing The Impacts

  • Species Elsewhere
  • Introduced
  • Established
  • Invasive
  • ×
  • Invasion Steps
  • Options
  • Prevention – exclude species of concern
  • Insure no propagules can escape cultivation
  • Rapid response - eliminate populations while small
  • Mitigate damage, control spread, eradicate if possible
  • Effective?
  • Yes
  • Unlikely
  • Unlikely – requires surveys and funds on hand
  • Eradication usually impossible, control is expensive

Summary: Part 1

Invasive aquatic plants have significant ecological and economic impacts in Indiana Most are intentionally introduced Current regulations are inadequate Preventing introduction is the best way to prevent future impacts

2. Species Available

What species are available?

  • Buy and identify organisms

What risks are posed?

  • Spread of known invaders
  • Introduction of new invaders

PPT Slide

Organisms Purchased

Risks Posed - Plants

Availability of known invasives

  • 45% of US restricted plants available over web
  • Eurasian watermilfoil, curly-leafed pondweed, water chestnut and many more invasive, or potentially invasive, species


  • 40% of Linnean names incorrect
  • Ambiguous common names


  • 5 snail species
  • 1 crustacean species
  • 2 insect species
  • duckweed (Lemna sp.)

Summary: Species Available

Watergarden and aquarium trades are spreading potential and known invaders Plants are often incorrectly identified by vendors Plant trade is a vector for the transfer of many contaminant species

Overall Conclusions

Invasive aquatic plant species are a significant economic and ecological problem in Indiana Preventing introduction is the best way to stop further damages Many actually or potentially invasive species are being spread through trades Risk assessment is possible and accurate