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Ecological and Economic Costs Associated with Hydrilla (Hydrilla verticillata)
Ecological Costs
Competition with native plants
  • Hydrilla can shade out native vegetation. (1)
  • Hydrilla outcompetes native Vallisneria americana in part by allocating more resources to producing reproductive propagules and by producing a much higher percentage of photosynthetic tissue vs. non-photosynthetic tissues. (2)
  • Though American pondweed (Potamogeton nodosus) was found to be a better than or equal competitor of Hydrilla, Hydrilla still managed to establish new individuals from axillary turions when grown in established American pondweed beds. (3)
  • With increased nutrient input, Hydrilla greatly outcompeted the native Vallisneria americana (when nutrients were limited the Vallisneria was the better competitor). This suggests that pollution/runoff could fuel successful invasion of Hydrilla. (4)
  • Continued presence of Hydrilla and other invasive plants decreased the available seed bank (and diversity of that seed bank) of native plants in a study of 21 New Zealand lakes. (5)
  • Application of sonar and aquathol-k in Lake Seminole (AL, FL, GA) to control Hydrilla allowed the establishment of native submerged aquatic vegetation. (6)
  • The stagnant water conditions created by heavy infestations of Hydrilla provide a breeding ground for mosquitoes. (1)
  • Hydrilla is a substrate for a toxic cyanobacteria linked to avian vacuolar myelinopathy, a disease linked to the death of bald eagles in the southeastern US. (7)
Impact on native fauna
  • Hydrilla provides poor habitat for fish and other wildlife. (1)
  • Dense mats of Hydrilla reduce the dissolved oxygen available in the infested body of water. (1)
  • Fish inhabiting the littoral zone (edge and shallow depths of basin) in Lake Marion, SC experienced population increases following removal of Hydrilla by grass carp. (8)
  • The spread of Hydrilla through the Atchafalaya River Basin in Louisiana along with reduced populations of coontail led to reduced habitat for phytophilous (plant-eating) macroinvertebrates. Hypoxia caused by Hydrilla reduced vertical distribution of macroinvertebrates in the littoral zone (edge and shallow depths of basin). (9)
  • Hydrilla managed with fluridone produced up to two times less organic sediment than when not managed, since unmanaged populations produced a thick matted surface layer with much more biomass to contribute to the sediment. (10)
  • An estimated 32% of fish numbers and 18% of fish biomass were lost during mechanical harvesting of Hydrilla in Orange Lake, FL, including small native species. (11)
Association with other introduced species
  • In Florida, the invasive South American fish Hoplosternum littorale uses Hydrilla to build nests, and built these nests preferentially in Hydrilla-infested areas. (12)
Economic Costs
Control Costs
  • Costs to the state of Maine to control Hydrilla in Pickerel Pond were $20,000-$25,000 per year from 2003 to 2006. (13)
  • Since 2002, Massachusetts has spent approximately $40,000 per year (a combination of state, town, and private funding) to manage hydrilla in a single pond in Barnstable County. (22)
  • Over $50 million was spent to manage Hydrilla in Florida during the 1980s. (1)
  • About $2.5 million per year is spent to manage Hydrilla in South Carolina. (1)
  • About $.5 million per year is spent to manage Hydrilla in North Carolina. (1)
  • It cost approximately $1200 per acre to harvest Hydrilla on the Potomac River in order to clear boat lanes. (1)
  • It cost $55 million to control Hydrilla in Florida from 1980-1991. (14)
  • In 1995 it was estimated that Florida needed $10 million for Hydrilla management, with $15 million estimated for 1996. (15)
  • Estimated costs to attain a proper fluridone concentration to control Hydrilla in Lake Tohopekaliga, FL in 2004 were $2 to $3 million, depending on water levels. (16)
  • Hydrilla coverage of 80% of Lake Orange (FL) tripled the cost of aquatic plant control on the lake in the late 1970s. (17)
  • Hydrilla eradication in two lakes in King County, WA cost an estimated $100,000/year starting in 2003. (18)
Loss of revenue
  • An estimated 32% of fish numbers and 18% of fish biomass were lost during mechanical harvesting of Hydrilla in Orange Lake, FL, including juvenile sportfish valued at a loss of $6000 per hectare. (11)
  • Hydrilla coverage of 80% of Lake Orange (FL) caused an 85% reduction in angler effort in 1977, leading to a 90% loss in revenue (about $1 million per year) due to limited lake access. (17)
  • Largemouth bass weight, growth and fecundity was considerably less in the part of Lake Seminole (AL, FL, GA) with dense (76%) coverage of submerged aquatic vegetation (mainly Hydrilla), vs. areas with 25% coverage. (17)
  • Recreational visitation to Lake Seminole (AL, FL, GA) declined as Hydrilla coverage increased, impacting the area's economy. This was possibly due to decline in largemouth bass catch. (19)
  • Young largemouth bass increased growth rate following removal of Hydrilla in Lake Seminole (AL, FL, GA), likely due to easier predation with clearing of vegetation. (20)
  • Hydrilla infestations have led to the temporary closing of boat marinas on both coasts of the US. (21)
Impact on Recreation and the Environment
  • Hydrilla interferes with recreational activities including swimming, boating, and fishing. (1)
  • Hydrilla interferes with the navigation of boats and other watercraft in heavily infested waters. (15)
  • Hydrilla reduces flow in drainage canals, and can cause flooding. (15)
Impact on Industry and General Economic Costs
  • Hydrilla can clog dam trash racks and intake pipes, impacting hydropower and irrigation systems. (1)
  • Hydrilla disrupts the cooling process in waters used for utility cooling. (15)
  • Hydrilla reduces flow in drainage canals, and can cause flooding. (15)
  • In 1991 problems with Hydrilla caused a hydroelectric plant in South Carolina to shut down, requiring over $2.5 million in repairs and control costs. This resulted in a loss of over $2 million in electricity that was not generated. (21)
  1. Hydrilla verticillata - Hydrilla - A Probem Aquatic Plant in the Western USA. Western Aquatic Plant Management Society. 2004.
  2. Community structure and competition between Hydrilla and Vallisneria. Haller and Sutton. 1975. Journal of Aquatic Plant Management. 13(1): 48+
  3. Interactions between American pondweed and monoecious hydrilla grown in mixtures. Spencer and Ksander. Hyacinth Control Journal. 2000. 38(1): 5+
  4. Competition between Hydrilla verticillata and Vallisneria americana as influenced by soil fertility. Van et al. Aquatic Botany. 1999. 62(4): 225-233
  5. The impact of invasive submerged weed species on seed banks in lake sediments. de Winton and Clayton. Aquatic Botany. 1996. 53(1-2): 31-45
  6. The Use of Herbicides to Control Hydrilla and the Effects on Young Largemouth Bass Population Characteristics and Aquatic Vegetation in Lake Seminole, Georgia. Maceina and Slipke. Journal of Aquatic Plant Management. 2004. 42(1): 5+
  7. A novel epiphytic cyanobacterium associated with reservoirs affected by avian vacuolar myelinopathy. Williams et al. Harmful Algae. 2007. 6(3): 343+
  8. Response of littoral fishes in upper Lake Marion, South Carolina following Hydrilla control by triploid grass carp. Killgore et al. Hyacinth Control Journal. 1998. 36(1): 82+
  9. Spatial Distribution of Macroinvertebrates Inhabiting Hydrilla and Coontail Beds in the Atchafalaya Basin, Louisiana. Colon-Gaud et al. Journal of Aquatic Plant Management. 2004. 42(2): 85+
  10. Organic sedimentation associated with Hydrilla management. Joyce et al. Hyacinth Control Journal. 1992. 30(1): 20+
  11. Fish Harvest Resulting From Mechanical Control of Hydrilla. Haller et al. Transactions of the American Fisheries Society. 1980. 109(5): 517-520
  12. Nests and Nest Habitats of the Invasive Catfish Hoplosternum littorale in Lake Tohopekaliga, Florida: A Novel Association with Non-native Hydrilla verticillata. Nico and Muench. Southeastern Naturalist. 2004. 3(3): 451-466
  13. Maine Department of Environmental Protection. 2007.
  14. Losses from Aquatic Weeds. Lach. Encyclopedia of Pest Management. 2002.
  15. Hydrilla verticillata (L.F.) Royle (Hydrocharitaceae), "The Perfect Aquatic Weed". Langeland. Castanea. 1996. 61: 293-304
  16. Hydrilla Management in Florida: A Summary and Discussion of Issues Identified by Professionals with Future Management Recommendations. Hoyer et al. Department of Fisheries and Aquatic Sciences, University of Florida. 2005.
  17. The Influence of Disparate Levels of Submersed Aquatic Vegetation on Largemouth Bass Population Characteristics in a Georgia Reservoir. Brown and Maceina. Journal of Aquatic Plant Management. 2002. 40(1): 28+.
  18. Pipe and Lucerne Lakes 2003 Hydrilla Eradication Project: Annual Report. King County Water and Land Resources Division. Department of Water Quality Washington State Department of Ecology. 2004.
  19. Analysis of the recreational fishery and angler attitudes toward Hydrilla in Lake Seminole, a southeastern reservoir. Slipke et al. Journal of Aquatic Plant Management. 1998. 36(2): 101+
  20. Changes in Diet and Food Consumption of Largemouth Bass Following Large-scale Hydrilla Reduction in Lake Seminole, Georgia. Sammons and Maceina. Hydrobiologia. 2006. 560(1): 109-120
  21. Hydrilla - Biological Control of Invasive Plants in the Eastern United States. Balciunus et al. in Van Driesche, R., et al., 2002, Biological Control of Invasive Plants in the Eastern United States, USDA Forest Service Publication FHTET-2002-04, 413 p.
  22. Massachusetts Department of Conservation and Recreation. 2007.
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