Lentis/World Trade as an Invasive Species Vector

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         “[An] aquatic nuisance species [is] a nonindigenous species that threatens the diversity or abundance of native species or the ecological stability of infested waters, or commercial, agricultural, aquacultural, or recreational activities dependent on such waters.”
           -Nonindigenous Aquatic Nuisance Prevention and Control Act, 1990[1]
A map of international shipping routes, which are major vectors for invasive species


Along with new trade opportunities, westward exploration by European adventurers introduced new species of organisms into the Americas. In the early 1500’s, European traders transported pigs to the Caribbean as well as what is now the US.[2] The pigs were left to reproduce and exist as a food source and economic trading good for the returning sailors. The US government classifies feral swine an invasive species, an organism that is non-native to an ecosystem and whose introduction causes or is likely to cause harm. Today, damage done by the wild pigs is estimated to be $1.5 billion in the US alone.[3] International trade has introduced many other species of nonnative organisms to the Americas that have impacts on local economies, native biodiversity, infrastructure, and legislation. Whether the invasive species have been intentionally and unintentionally introduced, local and international governments implement combative efforts against their detrimental effects.

Effects of Invasive Species[edit]

Environmental Impacts[edit]

Nonindigenous species force native species from their ecological niches and push them to extinction. They inhibit native species by outcompeting them for food and other necessary resources, spreading harmful diseases, and overtaking spawning grounds. Native wildlife lack defenses to deter the invader and cannot adapt to the abruptly disturbed food chain.[4] Biodiversity decreases as the invader forces native species out of the area. Diverse ecosystems, especially those prevalent with plants, can quickly devolve into vulnerable monocultures.[5] The invader can alter the environment by means beyond influencing biodiversity. Examples include driving out certain species that fix chemicals in the soil, leading to a change in the soil chemistry that natives are unable to adapt to. They can also increase the intensity of wildfires by killing trees and creating more dead wood, which can have adverse effects on indigenous species.[6]

Economic and Trade Impacts[edit]

Invasive species cause economic strain to affected areas. Worldwide, annual damages estimate to $1.4 trillion, with the U.S. totalling about $120 billion.[7] In the US, invasive species affect diverse ecosystems, including the wetlands of the south, mountains and forests of the north, and nearly every aquatic ecosystem. For instance, Florida spends $56 million a year to manage hydrilla, a water weed.[8]

Every invasive species poses an economic burden. They can cause massive losses in agricultural productivity by turning grazing lands into barren wastelands, increasing the frequency and intensity of wildfires, or introducing diseases to livestock and crops. The risk of spreading invasive species threatens an area’s imports and exports. Islands and isolated areas with fragile ecosystems, like Australia and Guam, must enact harsh trade restrictions to protect their environments.[9][10]

Property Damages[edit]

In 2005, the Office of Technology Assessment of the U.S. Congress has determined a worst case scenario of $97-$137 billion in damages related to 79 harmful species.[11] These costs consider damages to agriculture, forestry, fisheries and other water uses, utilities, buildings and natural areas. However, this range doesn’t account for impacts on dependent businesses and industry. Zebra mussels, for example, are an invasive species that cause 3.1 billion dollars in damages to hydroelectric plants. The damages considered by the US Congress do not account for the business losses for those counting on hydroelectric energy.[12]

Combative Efforts[edit]


The federal government passed the Nonindigenous Aquatic Nuisance Prevention and Control Act of 1990 in reaction to the spread of the zebra mussels in Great Lakes. The federal program worked to enforce a new policy for ballast water exchange in the ocean and to decrease the spread of mussels in the lakes. The program established a task force to enforce the new regulations. The Aquatic Nuisance Species Task Force included the U.S. Fish and Wildlife Service, the U.S. Coast Guard, the Environmental Protection Agency, the Army Corps of Engineers, the National Oceanic and Atmospheric Administration, and twenty other federal agencies. The federal government officially had a role in vessel operation regulation, education and training programs for industry and local residents, and ecological surveys of invasive species.[13]

The National Invasive Species Act of 1996 amended the established regulations and expanded the scope of influence beyond the Great Lakes region. The new act set a standard for exchanging ballast water outside the 200-mile US Exclusive Economic Zone and established expectations for ships to report their ballast water status when entering the zone. It added outreach and research to the ANS Task Force duties and began the development of state management plans.[14]

The Environmental Protection Agency published the Vessel General Permits in 2008 and 2013, which set standards for ships importing goods to the US. Multiple different groups filed lawsuits against the EPA’s issuance of the VGP’s. The Northwest Environmental Advocates, the Center for Biological Diversity, the Natural Resources Defense Council and the National Wildlife Federation sued the EPA for failing to uphold the agency’s responsibility as deemed in the Clean Water Act.[15] The CWA, passed in 1972, stated the EPA’s duty to protect US waters from pollutants. The court ruled in favor of the environmental groups, stating that invasive species are a dangerous form of pollution spreadable by vessels and recreational boats.[16] Three groups from the shipping industry and the state of Michigan also sued the EPA. All the groups agreed that the permits were too arbitrary and did not establish strict quantitative standards for boats. Due to inconsistencies between federal and local regulations, industries found it difficult to comply with permits.[17]

Local Efforts[edit]

The current state of legislation against invasive species is fairly unresolved. Quantitative standards are difficult to set. Ballast water treatments are nowhere near completely effective at ensuring no invasive species enter new waterways. Some regions have taken to other methods to mitigate the effects and control the number of invasive species.

In the Great Lakes region, recreational boaters are educated about the effects of invasive species, such as the zebra mussel. They are required to clean their boats when docking to mitigate the spread of the harmful species. Across the country, boaters and anglers are encouraged to report sightings of invasive aquatic fish and plants. For example, states in the Potomac River region have created hotlines and websites for reporting sightings of the invasive snakehead fish. In 2016, Maryland held a snakehead fishing derby to create awareness.[18]

Local restaurants have added invasive species to their menus to promote their gastronomical value and combat their population growth. In Baltimore, many restaurants have incorporated snakehead fish on their menus.[19] Cooking websites and environmental advocacy groups have compiled recipes that use invasive species as ingredients.[20]

Case Studies[edit]

Zebra Mussels[edit]

A zebra mussels encrusted current meter in Lake Michigan

As an invasive species, zebra mussels harm aquatic infrastructure and freshwater ecosystems. Beginning in the 1980’s, trading ships deposited them in the Great Lakes through ballast water discharge.[21] From there they spread up to Canada and down to freshwater ecosystems connected to the Mississippi River. zebra mussels originated in the Caspian Sea but flourish in the plankton rich waters of Midwest America. The zebra mussel consumes phytoplankton at high rates, which reduces the amount available to native species.[22] It is difficult to estimate the national economic impacts of zebra mussels because of their rampant population growth.

In 2012, zebra mussels caused damages estimated to be over $100 million to Great Lake hydroplant infrastructure.[23] Total US estimates for damages by zebra mussels to the Great Lakes from 1993-1999 was over $3 billion.[24]

The International Ballast Water Management Convention aims to slow down the spread of invasive species deposited from ballast tanks. They created basic regulations for ballast water before it is deposited back into a non-native ecosystem.[25] Such regulations include filtering systems and chemicals to destroy invasive species in the ballast tanks; however, filters aren’t efficient and chemicals can harm native species. Zebra mussels are resilient to predators, and can survive digestion. As a result, they can reside inside of a fish and be deposited in another body of water.[26]

Brown Tree Snake[edit]

A brown tree snake in its typical S shape

The brown tree snake came to Guam sometime in the late 1940s after stowing away on a cargo ship. Due to a lack of natural predators and an abundance of prey, the snake population quickly rose and caused the extirpation of the majority of the island’s native vertebrates. A dozen native bird species, for instance, were driven to extinction while others were classified as endangered or critically endangered.[27] The snakes cause thousands of power outages wreaking widespread economic damage to the island. Because of Guam’s status as a transportation hub in the Pacific, the brown tree snake has the potential to be accidentally introduced to other islands as stowaways on air traffic or cargo ships.[28]

Steps taken to prevent their spread include rigorous inspections and deploying search dogs on outbound vessels. Despite these efforts, the species has still been sighted on a number of other islands such as Wake Island, Okinawa, Hawaii, as well as Texas.[29] There have been multiple efforts to eradicate the snakes, including dropping Acetaminophen laced mice on the island, but that method’s effectiveness remains unclear.[30]


Kudzu on trees near Atlanta,Georgia

Kudzu was introduced to the United States in 1876 at the Centennial Exposition. It was marketed as an ornamental plant to shade porches, a cover to prevent soil erosion, and a cheap source of high-protein livestock fodder.[31] Throughout the early 1900s, the U.S. government subsidized the planting of kudzu, leading to 3 million planted acres by 1946. Changing economics and a number of blights and infestations forced farmers to urban areas, leaving their kudzu crops unattended. The kudzu grew rapidly in the southeastern U.S. climate and, by 1953, the government removed it from a list of suggested soil covers. By 1970, it was listed as a weed and was placed on the federal Noxious Weed List in 1997. Today, kudzu covers over 7.4 million acres of the southeastern U.S. and grows at an estimated rate of 120 thousand acres per year.[32]

Kudzu's range in the United States

Kudzu grows quickly and survives in nitrogen-poor areas, allowing it to gather resources and outcompete native species. As it takes over, kudzu damages or kills other plants by smothering them. It also completely cover trees, breaks their branches, and can even uproot them. As a result, areas infested with kudzu eventually become biologically homogenous “vine barrens,” where any other plant is unable to grow.[33] Kudzu causes between $100 to $500 million of damage annually due to lost productivity. It costs $5000 per 2.5 acres per year to control its spread, and power companies spend over $1.5 million annually to repair damaged power lines.[34] No current control methods are completely effective. Chemical treatments are ineffective for long term control, mechanical treatments are slow and expensive, and biological treatments like blights and insect predation have a high potential to hurt other species in the affected areas.[35] A relatively new potential treatment is to use wild goats and sheep to eat kudzu. A small herd can eat over an acre of kudzu a day with little chance to damage the rest of the environment. This treatment is not commonly used, though it is slowly spreading through kudzu affected areas.[36]

Asian Carp[edit]

An Asian Carp in the Mississippi River

In the 1970’s, southern states sought to filter waste water by reducing algae. Asian carp were imported as a solution, since they consume up to 20% of their bodyweight per day in plankton and can grow to over 100 pounds. However, flooding allowed them to escape into the Chicago Area Waterways System, towards the Great Lakes.[37]

Due to a lack of natural predators, a voracious appetite, and a high reproduction rate, they are overtaking native populations. A report to Congress in 2014 stated that Asian carp represent approximately 90% of the population density in the lower reaches of the Illinois River.[38]

The overpopulation has resulted in a 13% decrease in commercial fishing harvests compared to the national average historical averages from 1989 to 2005.[39] Since Asian carp are worth less than native fish, the reduction in commercial fishing harvests have greatly impacted local businesses. According to the Nature Conservancy, Asian carp are affecting nearly 125,000 jobs in the Great Lakes region.[40] To curb Asian carp population, the U.S. government has supported targeted commercial fishing. This method has reduced Asian carp by approximately 68% in the upper Illinois River. The Asian carp’s continued spread towards the Great Lakes has prompted the U.S. government to implement technological countermeasures. In 2002, the U.S. Army of Engineers built three Electric Dispersal Barriers to prevent interbasin transfer of fish between the Mississippi River and Great Lakes basins. These barriers consist of steel electrodes that generate an electric field in the water, which discourage fish from crossing.[41] The government has also researched methods to track Asian carp movement. Their primary method involves testing water samples for genetic material (environmental DNA, or eDNA) to determine carp distribution in the environment. This is a vital tool for early detection of invasive Asian carp, and allows groups to prepare accordingly.


Although trade has connected countries across hemispheres since westward colonization, it has also led to the spread of nonnative organisms. Invasive species are a new area of study that were first addressed by the U.S. government in 1996 through the National Invasive Species Act.[42] These unwelcome pests have caused billions of dollars in property damages, harmed native biodiversity, and limited economic growth.

While larger species, such as plants and animals, have been discussed, microorganisms are also a type of invasive species that significantly impact native organisms. Understanding how these diseases and bacteria are transported through international trade is vital in establishing preemptive actions to limit future impacts.


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  42. https://books.google.com/ngrams/graph?content=invasive+species&year_start=1990&year_end=2000&corpus=15&smoothing=3&share=&direct_url=t1%3B%2Cinvasive%20species%3B%2Cc0