Invasive Species: An Overview
Invasive species pose a significant threat to natural resources in the U.S.
According to Executive Order 13112, which established the National Invasive Species Council in 1999, invasive species are “non-native (or alien) to the ecosystem under consideration and whose introduction causes or is likely to cause economic or environmental harm or harm to human health.” Invasive species can be plants, animals or other organisms, such as microbes, which are introduced and spread either intentionally or unintentionally. Such invasive species can be introduced intentionally as crops, livestock, sport fish or pets, or unintentionally, such as by “hitchhiking” on ships.
Invasive species can dramatically alter local ecosystems by decreasing biodiversity, out-competing and displacing native plants and animals (which can compromise ecosystem health) and threatening endangered species. Further contributing to the threat posed by invasives is the alarming speed at which they can reproduce and spread.
They can also cause significant economic impacts. According to the seminal paper by David Pimentel, Lori Lach, Rodolfo Zuniga, and Doug Morrison, the economic damages associated with invasive species in the U.S. exceeds $120 billion per year. Costs associated with invasive species can range from implementing prevention programs, creating early detection and rapid response programs, conducting control and management activities, as well as researching and holding outreach campaigns and restoration programs. Additionally, invasive species can impact agriculture and potentially cause decreases in private property values. For example, the U.S. Fish and Wildlife Service estimates that U.S. agricultural production loses $13 billion/year from invasive insects alone.
The Threat of Aquatic Invasive Species
Aquatic invasive species may include plants or animals. Aquatic invasive plants are introduced plants that live in or next to water, while aquatic invasive species require water as their habitat—but do not necessarily live entirely in water. Aquatic invasive species are of particular concern for a variety of reasons. Many of them are unintentionally introduced and transported by accidental “hitchhiking” on ships traveling long distances or on equipment such as waders, anchors, buckets, etc. Plants, mud, and animals such as mussels can often cling to the exterior of boats and boat trailers, while water contained in ballast tanks and other boat compartments can also inadvertently spread alien species.
Because invasive species can spread rapidly, collaboration among states is essential. Coordinated prevention and enforcement campaigns are of particular importance when dealing with aquatic invasive species, as waters often cross or form state boundaries and people move species between state lines knowingly or unknowingly. Various regional approaches, enforcement programs, task forces and public outreach and education campaigns aim at combating the threat of invasives. Numerous aquatic invasive regional task forces and committees exist to coordinate efforts in combating aquatic invasives. Both state and interstate aquatic invasive management plans have been growing in efforts to limit their spread. Additionally, numerous states have enacted laws addressing such threats. For a detailed compilation of state invasive species laws, visit the National Invasive Species Information Center State Laws and Regulations site.
Below are a few prominent aquatic invasive species impacting U.S. waters and threatening ecosystems and the economy. For more information on specific aquatic invasive species, visit the National Invasive Species Information Center’s partial listing of aquatic invasive species.
Seven species of Asian carp have been introduced to the U.S, of which silver, bighead, black and grass carp are considered the greatest threats. Silver and bighead carp can grow quite large, reaching up to 100 pounds and lengths of over four feet. Invasive Asian carp are a threat to ecosystems throughout the U.S., consuming native vegetation, out-competing native fish, disrupting local ecosystems and introducing new pests and diseases. Invasive carp not only out-compete native aquatic wildlife, but they can drastically alter the food web and overall aquatic system by impacting fish, invertebrate and plant communities. Some carp, such as silver carp, reproduce prolifically and can cause further damage by feeding on plankton necessary for mussels and larval fish to thrive. Furthermore, the sheer size of some carp has been known to injure boaters—silver carp often jump out of the water when disturbed.
Carp were introduced to U.S. waters either accidentally, as byproducts of other carp stock, or as a means of phytoplankton control for aquaculture purposes. Specifically, silver and bighead carp were imported as a mechanism of controlling algae in fish farms in the 1970s. However, after flooding in the 1990s, the carp escaped into the Mississippi River. Carp have systematically progressed north and can now be found in the Illinois River.
Asian Carp and the Great Lakes Region
Asian carp are of particular concern to states in the Great Lakes Region. In fact, the federal government deems Asian carp to be the most acute aquatic invasive species threat facing the Great Lakes. Economic and environmental damage from invasive species in the Great Lakes Basin is already estimated at $5.7 billion per year, and both commercial and sport fishing in the Great Lakes Basin have suffered losses estimated at $4.5 billion. If established in the Great Lakes, Asian carp will be difficult to control, with some experts declaring that it will be impossible to eradicate them from the Great Lakes.
Although it is believed that Asian carp have not yet made it to the Great Lakes, they are established in the Mississippi and Missouri Rivers and have already caused harm. A main pathway for Asian carp to arrive in the Great Lakes is through the Chicago River. The Chicago Sanitary and Ship Canal is the only shipping link between the Mississippi River and the Great Lakes region, making it a key route for Asian carp.
Asian carp have been confirmed 25 miles downstream from an electric barrier created by the U.S. Army Corps of Engineers to thwart Asian carp from entering Lake Michigan. Additionally, in 2010 a live Bighead carp was discovered on the Lake Michigan side of the barrier. DNA testing has also confirmed the presence of silver carp in Lake Michigan, suggesting that both silver and bighead carp may exist between Lake Michigan and the electric barrier. In response, the state of Michigan filed a lawsuit with the U.S. Supreme Court asking for the Chicago Sanitary and Ship Canal to be immediately closed. In turn, the state of Illinois filed a counter-suit, claiming that the closure of the canal would result in severe economic losses resulting from the impeded movement of ships. Both the U.S. Supreme Court and the U.S. Court of Appeals have rejected requests for preliminary injunctions to close the canal.
Many states have formed multi-state coalitions to manage the spread of Asian carp. In the Midwest, Asian Carp Regional Coordinating Committees have been working towards implementing control programs to prevent the introduction and spread of such invasive species. Their mission is to protect and maintain the integrity and safety of the Great Lakes ecosystem.
In the past few years, numerous states have adopted resolutions and bills to prevent the arrival of Asian carp. States such as Michigan, Minnesota, and Ohio have set aside money for education, research, rapid response, prevention and control. States have also created funds to implement programs aimed at combating the spread of Asian carp. Additionally, in this legislative session, Michigan adopted the Asian Carp Protection Resolution (SR 22), which encourages the Chicago Area Waterway System Advisory Committee to consider a variety of options to protect the Great Lakes from Asian carp. Missouri enacted HB 6, which appropriates money to the Fisher Delta Research Center in order to fund a public-private partnership for the control of Asian carp in Missouri.
Quagga and Zebra Mussels
Similar in appearance, both zebra and quagga mussels are invading U.S. waters. Native to Eastern Europe, such mussels were first discovered in North America in the late 1980s in the Great Lakes, transported in the ballast water of ships. By the 1990s, these tiny mussels had escaped from the Great Lakes and rapidly spread throughout the Hudson and Illinois Rivers, eventually making their way throughout the Mississippi Drainage basin. These mussels have been moving west and have been found as far west as California. As many as 10 trillion quagga and zebra mussels are in the Great Lakes today.
Quagga mussels differ from zebra mussels in that they have the ability to adapt to cold water temperatures and live in softer sediments, such as mud. Zebra mussels, on the other hand, attach to virtually any stable substrate or surface. Though the average lifespan of quagga and zebra mussels is only five years, each one will produce approximately 5 million eggs during this time. This rapid reproduction contributes to the speed with which they can spread.
Both zebra and quagga mussels feed on phytoplankton, which reduces food for native fish. While this causes an increase in water clarity due to filter feeding, it also creates ideal conditions for algae growth. In turn, deadly algae blooms have grown and spread in recent years. This increase in algae also causes botulism outbreaks that kill fish and aquatic birds.
In addition to causing declines in native populations by stripping the food web, they can also ruin beaches and attach to boats, water intake pipes, and any other structure, causing significant economic and structural damage. This in turn damages recreational industries (such as tourism and fishing) and can cause decreases in property values. According to estimates from the Center for Invasive Species Research at the University of California-Riverside, it costs over $500 million per year to manage mussels attached to power plants, water systems, industrial complexes, and boats/docks in the Great Lakes. A 2009 study by the U.S. Army Corps of Engineers noted that invasive mussels could cause losses of $22 million per year to the Lake Tahoe Region alone.
As with many invasives, prevention is the key to controlling zebra and quagga mussels. Many states are seeking to limit the spread of these invasive nuisances, while other states are proactively attempting to thwart the introduction of mussels in their waters. Numerous states have developed action plans for preventing and controlling invasive mussels, such as the Quagga-Zebra Mussel Action Plan for Western U.S. Waters, the Lake Tahoe Region Aquatic Invasive Species Management Plan, and the Columbia River Basin Interagency Invasive Species Response Plan: Zebra Mussels and Other Dreissenid Species.
With the looming threat of invasive mussels, many states have implemented watercraft inspection and decontamination (WID) programs. Western states, facing the potential introduction of these invasives, have implemented numerous WID programs. Such programs aim to reduce the introduction and spread by inspecting and decontaminating watercraft and equipment by trained personnel. While not necessarily specific to invasive mussels, these programs aim to check the spread of invasives by requiring owners of water vessels to pass through certain checkpoints.
In the 2015 legislative session, a number of states considered bills related to checkpoints for aquatic invasive species—Maryland, Minnesota, Montana, Nebraska, New Hampshire, Nevada, Oregon, Utah and Wyoming—three of which have been enacted.
Examples of state legislation:
- Montana (2015 HB 553—Enacted): Authorizes entities to operate check stations that, to the greatest extent possible, will be coordinated with the Department of Transportation and the Department of Fish, Wildlife, and Parks.
- Maryland (2015 HB 86—Enacted): Prohibits an owner of a vessel from placing it in a lake at a public ramp or dock if the owner has not taken certain actions, including cleaning the vessel and removing all visible organic material.
- Nevada (2015 AB 82—Enacted): Prevents a person from operating a boat in state waters unless the owner has paid a fee and attached an aquatic invasive species decal to the watercraft.
- Oregon (2015 HB 2207—Pending): Implements alternative ballast water management strategies for vessels when they empty their ballast tanks (another potential pathway for the introduction of aquatic invasives).
Invasive Aquatic Plants
Aquatic invasive plants are also of concern. They can impede boaters and swimmers, decrease property value, clog waterways, degrade native ecosystems and impact tourism and recreational fishing. Since non-native plants have few controls in their new habitat, they spread rapidly. While not a complete list, common aquatic invasives include alligator weed, curly pondweed, Eurasian watermilfoil, hydrilla, common and giant reed and water hyacinth.
States are taking aim at fighting aquatic invasive species. At least 10 states are considering legislation that creates either aquatic species funds or management programs—Alaska, California, Massachusetts, Michigan, Montana, New Hampshire, New Jersey, Nevada, Oregon and Vermont.
Examples of State Legislation:
- Nevada (2015 AB 82—Enacted): Provides that a person who knowingly or intentionally introduces an aquatic invasive species into state waters is guilty of a misdemeanor (for a first offense).
- Vermont (2015 SB 45—Pending): Exempts the use of 15 forms of aquatic nuisance controls from certain permit requirements. Normally, pesticides, chemicals, biological controls, structural barriers, mechanical devices, etc. cannot be used in state waters to control invasive aquatic plants and animals. However, this bill allows for exemptions from this requirement if certain conditions are met.
The Threat of Terrestrial Invasive Species
While the danger that Asian carp, zebra mussels and other aquatic invasive species pose are fairly well-known, non-native plants, insects, reptiles and mammals can also be highly destructive.
Invasive Plant Species
Thousands of land-based invasive plants have taken root in the U.S. Some of the most common are Canada thistle, cheatgrass, English ivy, garlic mustard, Japanese knotweed, kudzu, Norway maple, and purple loosestrife.
Most invasive plants have astounding reproductive capacity, producing large quantities of seed with high germination rates. In addition, some have aggressive root systems that can spread long distances from a single plant. The roots often grow so densely that they smother nearby native vegetation.
As native plant species are displaced by invaders at alarming rates, habitat for wildlife is also damaged. According to the U.S. Forest Service, invasive species have contributed to the decline of 42 percent of threatened and endangered species. For 18 percent of these species, invasives are the main cause of their decline.
In addition to impacts on wildlife, the spread of invasive plants can degrade water quality, increase soil erosion, contribute to wildfires and reduce agricultural production.
Management of invasive plants costs states millions of dollars per year. California, for example, spends $82 million each year on control, monitoring and outreach for invasive plants alone, according to a 2008 survey.
At least 47 states maintain a list of plants considered legally “noxious,” a term used interchangeably with invasive. Plants identified in these lists cannot be sold, transported, or propagated within the state unless authorized by permit. State laws also specify a variety of control methods for noxious weeds, including mechanical, cultural, biological, preventive and chemical.
Examples of State Legislation:
- Idaho (2015 SB 1073—Enacted): Authorizes the Director of the state Department of Agriculture to order the collection, removal and movement of noxious weeds from an infested area to a facility within the state for purposes of biological control research.
- New Jersey (2015 AB 3125/SB 2694—Pending): Prohibits a person from knowingly selling, offering for sale, planting, propagating, or otherwise distributing any invasive plant, except for science or educational purposes with a permit. The bill identifies nine invasive plant species and provides for civil penalties up to $500.
- Washington (2015 HB 1654—Pending): Directs the state noxious weed board to conduct a pilot project that evaluates the advantages of replacing pollen and nectar-rich noxious weeds preferred by honeybees, with native or non-invasive plants that can produce similar levels of pollen and nectar to support honeybee populations.
Also known as the “vine that ate the South,” Kudzu is one of the most prolific invasive plant species in the world. The hardy, fast-growing vine was first introduced to the U.S. in 1876, where it was featured at the Philadelphia Centennial Exposition. Today, kudzu is found in over 30 states, concentrated in the Southeast. Growing up to one foot per day, kudzu covers everything in its path—from grasses to mature trees. The result is large-scale alteration of natural ecosystems.
Invasive Animal Species
Invasive insects, mammals and reptiles are also of concern. Whether they arrived accidentally on cargo ships or were intentionally sold as pets, invasive animals cause serious harm to natural ecosystems and cost states and the federal government billions of dollars each year. The brown tree snake, Burmese python, giant African snail, nutria and wild boar are just a few of the species receiving national attention.
Invasive beetles, moths and other insects are destroying millions of trees across the country. Non-native insects have no predators in their new home and the trees have no natural defenses against them. Top offenders include the Asian longhorned beetle, Asian citrus psyllid, brown marmorated stink bug, European gypsy moth and emerald ash borer.
The emerald ash borer is the most destructive of the group. The metallic green beetle native to Asia and Eastern Russia was first discovered in the U.S. in 2002 and has since spread to 25 states. As its name suggests, the emerald ash borer infests ash trees, killing them within one to four years. A total of 7 billion trees are at risk.
Tree pests and pathogens often enter new ecosystems through the movement of firewood. State laws aimed at preventing new infestations often encourage the use of local firewood.
Examples of State Legislation:
- Maine (2015 HB 789—Pending): Establishes a firewood emergency response group to address reports of infestation of firewood by invasive species. The bill also creates a fund to educate the public on the dangers of infestation through imported firewood.
- Vermont (2014 HB 799—Enacted): Requires the Commissioner of Forests, Parks and Recreation to adopt rules regulating the importation of untreated firewood due to the potential to spread invasive species.
- NCSL’s Natural Resources and Infrastructure Committee hosts a spring webinar series, one of which will explore state efforts addressing invasive species.