Non-native invasive species pose a significant threat to aquatic ecosystems and can disrupt the use of invaded systems. For example, alien plants often outcompete indigenous flora and form monocultures that cannot be used by native fauna, which require a diverse habitat to thrive (Dibble et al., 1996; Jeppesen et al., 1998; Madsen, 2014). In addition to reducing the richness of the species, invasive species can modify ecosystem services. Aggressive growth of alien species can change soil texture and deplete substrate nutrient reservoirs, resulting in insufficient resource availability for native flora (Madsen, 2014). Exotic trees may produce dense canopies that reduce the amount of light available for photosynthesis by understory plants. A similar situation occurs in aquatic ecosystems; rapid growth and expansion by floating [e.g., waterhyacinth (Eichhornia crassipes)], floating-leaved [e.g., crested floatingheart (Nymphoides cristata)], and canopy-forming submersed [e.g., hydrilla (Hydrilla verticillata)] introduced species can interfere with the air–water interface, thereby blocking light, reducing oxygen in the water column, and degrading the habitat for native flora and fauna (Madsen, 2014).
Dense growth of exotic plants can interfere with anthropocentric interests. Terrestrial weeds can reduce crop yields by diverting water, nutrients, and other resources from cultivated plants and cause power outages and flooding (Bridges, 1994; Duryea and Kampf, 2017). Excessive growth of terrestrial invaders can exacerbate wildfires (Brooks et al., 2004). Fast-growing weedy trees in Florida and other hurricane-prone regions may be ill-suited for heavy rains and high winds; ultimately, they may become projectiles, damage power lines, or crush residential and commercial properties (Duryea and Kampf, 2017).
Aquatic ecosystems are not immune to the hazards posed by invasive species. In fact, some argue that the problems associated with the introduction of exotic plants are more pronounced in these unique ecosystems. Crop production is somewhat uncommon in aquatic areas, but yields of aquatic food crops can be greatly reduced when invasive species are present. Weed pressure is considered a major limiting factor for rice (Oryza sativa) production, with losses that range from 10 to 100% in the absence of weed management efforts (Rao et al., 2007). Similar to terrestrial weeds, aquatic invaders pose risks to human health by creating a drowning hazard and serving as a habitat for undesirable insects [e.g., mosquitoes (Anopheles sp., Aedes sp. Culex sp., Mansonia sp., and others)] that vector human disease (Cuda, 2014). Aquatic weeds can impact human uses of waterbodies by disrupting hydropower operations, clogging irrigation intakes, blocking access to recreational resources, interfering with the use of watercraft, and reducing aesthetics (and property values) (Holm et al., 1969). Overgrowth of aquatic plants can also inhibit water movement and negatively impact flood control operations, thereby increasing the risk of catastrophic flooding of communities, farms, roadways, and other anthropocentric infrastructure during heavy rainfall events (Grant, 1962).
It is clear that invasive plants cause a wide variety of problems, but how are these species able to produce such large and troublesome populations? Exotic species can become weedy and exhibit aggressive growth in an invaded region for a number of reasons. Abiotic factors such as temperature, rainfall, and nutrient availability may be more amenable in the invaded range compared to the native habitat of the species, thus fostering growth at levels not seen in the home territory of the invader. An important biotic factor that can result in explosive growth of a non-native species is the lack of specialist biological stressors in the introduced range. This phenomenon is often referred to as the “enemy release hypothesis,” and it posits that phytopathogenic organisms (primarily fungi and bacteria) and phytophagous animals (e.g., insects) that have co-evolved with the species in question prevent aggressive growth of the plant in its native range. When a plant is introduced to a new ecosystem where these stressors are not present, they are “released” from the pressure imposed by these organisms and can experience unchecked growth in the invaded range (Keane and Crawley, 2002). This hypothesis forms the basis of classical biological control, which uses the introduction of co-evolved host-specific insects or pathogens as a means to manage invasive species. This strategy has been used with varying levels of success to reduce populations of a variety of noxious weeds, including waterhyacinth (Tipping et al., 2014), alligatorweed [Alternanthera philoxeriodes (Buckingham, 1996)], and air potato [Dioscorides bulbifera (Center et al., 2015)]. However, indigenous herbivores that are present in the invaded range are often polyphagous and feed indiscriminately on both native and exotic plants. In fact, Macel et al. (2017) suggested that exotic plants may be more susceptible to herbivory by phytophagous generalists in newly invaded regions compared to indigenous plants. Therefore, the release from herbivory is incomplete and invasion success is likely influenced by a combination of abiotic and biotic factors.
By definition, invasive species are introduced and not native to the ecosystem in which they become problematic (U.S. Department of Agriculture, 1999). However, it is becoming evident to resource managers that excessive growth of indigenous plants can cause similar ecosystem disruptions. The reasons for formerly well-behaved plants “going rogue” and overtaking formerly diverse areas are unclear, but several factors may contribute to these new growth patterns. For example, warmer average temperatures may facilitate range expansion by allowing plants to move into areas that have become newly hospitable (Upson et al., 2016). Extirpation or reduction of natural enemies may occur in response to changing environmental conditions, disease, predation, and intentional or inadvertent pest control operations. An important factor that seems to drive weedy behavior in native aquatic plants is what I term “competition release,” or targeted management of introduced invasive species. Similar to the enemy release hypothesis, competition release frees native plants from competition with exotic species and allows them access to formerly unavailable resources such as light and nutrients. If the management techniques used do not include physical removal of the undesired plant material, then additional nutrient pulses are likely to occur as the dying plants decompose (Grimshaw, 2002; Jewell, 1971), which can further subsidize excessive growth by native plants.
The most intuitive way to address invasive behavior in native aquatic plants is to discuss them in the context of introduced exotic weeds with similar growth habits. The characteristics of representative floating, floating-leaved, submersed, and littoral (shoreline and shallow water) invaders are outlined and “weedy” native plants that are analogous to these exotic species are described in this work.
BlackburnR.D.WeldonL.W.YeoR.R.TaylorT.M.1969Identification and distribution of certain similar-appearing aquatic weeds in FloridaHyacinth Control J.81721
BrooksM.L.D’AntonioC.M.RichardsonD.M.GraceJ.B.KeeleyJ.E.DiTomasoJ.M.HobbsR.J.PellantM.PykeD.2004Effects of invasive alien plants on fire regimesBioscience54718
BuckinghamG.R.1996Biological control of alligatorweed, Alternanthera philoxeroides, the world’s first aquatic weed success storyCastanea61318
California Department of Food and Agriculturen.dCalifornia noxious weeds: Mexican waterlily or banana waterlily [Nymphaea mexicana Zucc.]. 30 Jan. 2019. <https://www.cdfa.ca.gov/plant/IPC/encycloweedia/weedinfo/nymphaea.htm>
CenterT.D.OverholtW.A.RohrigE.RayamajhiM.2015Classical biological control of air potato in Florida. Univ. Florida Inst. Food Agr. Sci. IFAS Publ. ENY-864. 16 Jan. 2019. <https://edis.ifas.ufl.edu/pdffiles/IN/IN95700.pdf>
City of Orlandon.dOrlando Wetlands Park: History. 30 Jan. 2019. <http://www.cityoforlando.net/wetlands/history/>
CudaJ.P.2014Aquatic plants mosquitoes and public health p. 31–36. In: L.A. Gettys W.T. Haller and D.G. Perry (eds.). Biology and control of aquatic plants: A best management practices handbook. 3rd ed. Aquatic Ecosystem Restoration Foundation Marietta GA
DibbleE.D.KillgoreK.J.HarrelS.L.1996Assessment of fish-plant interactions. Multidimensional approaches to reservoir fisheries managementAmer. Fish. Soc. Symp.16357372
DickG.O.SmartR.M.SnowJ.R.2005Propagation and production of native aquatic plants. ERDC/TN APCRP-EA-11. U.S. Army Eng. Res. Dev. Ctr. Omaha NE
DiTomasoJ.M.HealyE.A.2003Aquatic and riparian weeds of the West. Univ. California Agr. Natural Resources CANR Publ. 3420
DuryeaM.L.KampfE.2017Wind and trees: Lessons learned from hurricanes. Univ. Florida Inst. Food Agr. Sci. IFAS Publ. FOR 118. 16 Jan. 2019. <https://edis.ifas.ufl.edu/pdffiles/FR/FR17300.pdf>
FlemingJ.P.MadsenJ.D.DibbleE.D.2011Macrophyte re-establishment for fish habitat in Little Bear Creek Reservoir, Alabama, USAJ. Freshwat. Ecol.26118
FlimlinG.PomeroyR.2008Growing ornamental aquatic plants as a business in the northeastern United States. Northeastern Reg. Aquacult. Ctr. College Park MD
Florida Department of State2008Rule chapter 5B-64: Aquatic plant importation transportation non-nursery cultivation possession and collection. 22 Jan. 2019. <https://www.flrules.org/gateway/ChapterHome.asp?Chapter=5B-64>
Florida Department of State2014Rule chapter 5B-57.007: Introduction or release of plant pests noxious weeds arthropods and biological control agents. 22 Jan. 2019. <https://www.flrules.org/gateway/ChapterHome.asp?Chapter=5B-57>
Florida Exotic Pest Plant Council2017Florida Exotic Pest Plant Council 2017 list of invasive plant species. 12 Feb. 2019. <http://bugwoodcloud.org/CDN/fleppc/plantlists/2017/2017FLEPPCLIST-TRIFOLD-FINALAPPROVEDBYKEN-SUBMITTEDTOALTA.pdf>
Florida Fish and Wildlife Conservation Commission2014Florida Fish and Wildlife Conservation Commission annual report of activities conducted under the Cooperative Aquatic Plant Control Program in Florida public waters for fiscal year 2013-2014. 25 Feb. 2019. <https://myfwc.com/media/3200/aquaticplantmanagement-2013-2014.pdf>
Florida Fish and Wildlife Conservation Commission2015Florida Fish and Wildlife Conservation Commission annual report of activities conducted under the Cooperative Aquatic Plant Control Program in Florida public waters for fiscal year 2014-2015. 25 Feb. 2019. <https://myfwc.com/media/3201/aquaticplantmanagement-fy14-15.pdf>
Florida Fish and Wildlife Conservation Commission2016Florida Fish and Wildlife Conservation Commission annual report of activities conducted under the Cooperative Aquatic Plant Control Program in Florida public waters for fiscal year 2015-2016. 25 Feb. 2019. <https://myfwc.com/media/3193/annualreport15-16.pdf>
Florida Fish and Wildlife Conservation Commission2017Florida Fish and Wildlife Conservation Commission annual report of activities conducted under the Cooperative Aquatic Plant Control Program in Florida public waters for fiscal year 2016-2017. 25 Feb. 2019. <https://myfwc.com/media/3194/annualreport16-17.pdf>.
Florida Fish and Wildlife Conservation Commission2018Florida Fish and Wildlife Conservation Commission annual report of activities conducted under the Cooperative Aquatic Plant Control Program in Florida public waters for fiscal year 2017-2018. 25 Feb. 2019. <https://myfwc.com/media/19112/annualreport17-18.pdf>
GettysL.A.2005Inheritance of morphological characters of pickerelweed (Pontederia cordata L.). PhD Diss. Univ. Florida Gainesville. 15 Feb. 2019 <http://etd.fcla.edu/UF/UFE0009585/gettys_l.pdf>
GettysL.A.2014Waterhyacinth: Florida’s worst floating weed. Univ. Florida Inst. Food Agr. Sci. IFAS Publ. SS-AGR-380. 15 Jan. 2019. <https://edis.ifas.ufl.edu/ag385>
GettysL.A.Della TorreC.J.ThayerK.M.MarkovichI.J.2017Asexual reproduction and ramet sprouting of crested floatingheart (Nymphoides cristata)J. Aquat. Plant Mgt.558388
GettysL.A.EnloeS.F.2016Hydrilla: Florida’s worst submersed weed. Univ. Florida Inst. Food Agr. Sci. IFAS Publ. SS-AGR-444. 15 Jan. 2019. <http://edis.ifas.ufl.edu/pdffiles/AG/AG40400.pdf>
GettysL.A.HallerW.T.2013Effect of ecotype, sediment composition, and fertility level on productivity of eight Florida ecotypes of american eelgrass (Vallisneria americana)J. Aquat. Plant Mgt.51127131
GettysL.A.MooreK.A.Orozco ObandoW.2013Effect of sediment type and fertility level on growth of swamp rosemallow (Hibiscus grandiflorus Michx.)Proc. Florida State Hort. Soc.126321324
GettysL.A.PetersS.J.SuttonD.L.2001Culture and production of pickerelweed using three different substratesProc. Florida State Hort. Soc.114252254
GodfreyR.K.WootenJ.W.1979Aquatic and wetland plants of southeastern United States: Monocotyledons. Univ. Georgia Press Athens GA
GrimshawH.J.2002Nutrient release and detritus production by herbicide-treated freely floating aquatic vegetation in a large, shallow subtropical lake and riverArch. Hydrobiol.153318
HaberlandM.2016Ecology and control of the freshwater aquatic plant spatterdock (Nuphar sp.). Rutgers Univ. New Jersey Agr. Expt. Sta. Coop. Ext. Fact Sheet FS1255. 30 Jan. 2019. <https://njaes.rutgers.edu/fs1255/>
HaugE.J.2018Monoecious hydrilla and crested floating heart biology and the response of aquatic plant species to florpyrauxifen-benzyl herbicide. PhD Diss. North Carolina State Univ. Raleigh. 26 Jan. 2019. <https://repository.lib.ncsu.edu/bitstream/handle/1840.20/35124/etd.pdf?sequence=1>
HolmL.G.PlucknettD.L.PanchoJ.V.HerbergerJ.P.1977The world’s worst weeds: Distribution and biology. Univ. Press of Hawaii Honolulu HI
JaggersB.V.1994Vallisneria americana: Considerations for restoration in Florida. Florida Game and Fresh Water Fish Commission Eustis FL
JeppesenE.SondergaardM.SondergaardM.Christoffersen (eds.)K.1998The structuring role of submerged macrophytes in lakes. Springer-Verlag New York NY
LesD.S.MehrhoffL.J.1999Introduction of nonindigenous aquatic vascular plants in southern New England: A historical perspectiveBiol. Invasions1281300
MacelM.DostálekT.EschS.BucharováA.van DamN.M.TielbörgerK.VerhoevenK.J.F.MünzbergováZ.2017Evolutionary responses to climate change in a range expanding plantOecologia184218
MadeiraP.VanT.StewardD.SchnellR.1997Random amplified polymorphic DNA analysis of the phenetic relationships among world-wide accessions of Hydrilla verticillataAquat. Bot.59217236
MadsenJ.D.2014Impact of invasive aquatic plants on aquatic biology p. 1–11. In: L.A. Gettys W.T. Haller and D.G. Perry (eds.). Biology and control of aquatic plants: A best management practices handbook. 3rd ed. Aquatic Ecosystem Restoration Foundation Marietta GA
MooreK.A.FisherL.E.Della TorreC.J.IIIGettysL.A.2015Native aquatic and wetland plants: Duck potato Sagittaria lancifolia. Univ. Florida Inst. Food Agr. Sci. IFAS Publ. SS-AGR-399. 15 Jan. 2019. <https://edis.ifas.ufl.edu/ag403>
SchoelynckJ.BalK.VerschorenV.PenningE.StruyfE.BoumaT.MeireD.MeireP.TemmermanS.2014Different morphology of Nuphar lutea in two contrasting aquatic environments and its effect on ecosystem engineeringEarth Surf. Process. Landf.391518
ShillingD.G.HallerW.T.1989Interactive effects of diluent pH and calcium content on glyphosate activity on Panicum repens L. (torpedograss)Weed Res.29618
SlagleZ.J.AllenM.S.2018Should we plant macrophytes? Restored habitat use by the fish community of Lake Apopka, FloridaLake Reserv. Mgt.34318
TippingP.W.MartinM.R.PokornyE.N.NimmoK.R.FitzgeraldD.L.DrayF.A.JrCenterT.D.2014Current levels of suppression of waterhyacinth in Florida USA by classical biological control agentsBiol. Control716569
UpsonR.WilliamsJ.J.WilkinsonT.P.ClubbeC.P.MacleanI.M.D.McAdamJ.H.MoatJ.F.2016Potential impacts of climate change on native plant distributions in the Falkland IslandsPLoS One1111e0167026doi: 10.1371/journal.pone.0167026
U.S. Department of Agriculture1999Executive orders for invasive species: Executive Order 13112. 25 Feb. 2019. <https://www.invasivespeciesinfo.gov/executive-order-13112-section-1-definitions>
U.S. Department of Agriculturen.dNatural Resources Conservation Service PLANTS database: Nymphaea mexicana Zucc. 25 Jan. 2019. <https://plants.usda.gov/core/profile?symbol=NYME>
WebbM.A.OttR.A.JrBondsC.C.SmartR.M.DickG.O.DoddL.2012Propagation and establishment of native aquatic plants in reservoirs (Data Series No. 273). Texas Parks and Wildlife Department Inland Fisheries Division Austin TX
Weeds Trees and Turf1970Aquatic weed researcher Dr. Lyle Weldon drowns. Weeds Trees Turf 9(3):49. 31 Jan. 2019. <http://archive.lib.msu.edu/tic/wetrt/article/1970mar.pdf>
WennerbergS.2004United States Department of Agriculture Natural Resources Conservation Service plant guide: Yellow pond-lily (Nuphar lutea) (L.) Sm. 15 Jan. 2019. <https://plants.usda.gov/plantguide/pdf/pg_nulu.pdf>
WestbrookR.G.McCordL.2010EDRR fact sheet: Crested floating heart. 30 Jan. 2019. <http://nceppc.weebly.com/uploads/6/8/4/6/6846349/crested_floating_heart.pdf>