The Great Lakes’ Most Unwanted

Aquatic invasive species (AIS) are plants, animals, and other organisms that end up in lakes, rivers, and oceans where they don't naturally belong. Imagine them as uninvited guests that crash nature's delicate party. These creatures can hitch a ride to new locations in various ways—often with a little help from us humans. They might travel across the world in the ballast water of huge cargo ships, get released into the wild by aquarium owners, or cling onto boats and fishing gear.

Once these invasive creatures get comfortable, they can cause all sorts of trouble in their new homes. They gobble up food and space, squeezing out the local wildlife that are supposed to be there (National Oceanic and Atmospheric Administration 2024.). They can also bring in diseases, disturb the balance of the ecosystem, and even impact our fishing and boating spots (Pimentel et al. 2005).

Most people might not think much about the plants and animals living in our lakes and rivers, but when unexpected visitors show up, they can stir up quite the commotion. These aquatic invasive species are a big deal for a few reasons—they can harm the environment, cost us a lot of money, and can even be a risk to our health.

Tackling these unwelcome intruders is a serious job that involves scientists, government agencies, and everyday folks working together to keep our waters healthy. It's a bit like neighborhood watch, but for our lakes and rivers. We all play a part, whether it's by cleaning our boats before moving to new waters or being careful with our aquarium pets (Rixon et al. 2005).

 The history of aquatic invasive species in the Great Lakes is a long and challenging saga, beginning in the early 19th century with the construction of the Erie Canal, which opened a pathway for species to move between the Atlantic Ocean and the Great Lakes. The problem escalated with advancements in shipping technology, particularly following the opening of the Saint Lawrence Seaway in 1959, allowing ocean-going vessels to bring foreign species into the lakes through ballast water discharge. Use the interactive slider on the map below to view the changes in aquatic invasive species after the Seaway opened.

Notable invaders such as the zebra mussel, sea lamprey, and quagga mussel have since wreaked havoc on the Great Lakes ecosystem, altering food webs and outcompeting native species. These invasions have prompted extensive research and management initiatives, including international cooperation between the United States and Canada, to mitigate impacts and prevent further spread of these biological invaders. Research continues on the impact of the species that have already been introduced – and on potential future invaders at our doorstep.

The GLANSIS organism impact assessment is a specialized method created to determine the specific effects an invasive species might have on the Great Lakes ecosystem. This method examines several factors about the organism in question, such as its ability to survive, reproduce, and spread in the Great Lakes environment, as well as its potential to compete with native species, alter habitats, or bring diseases. The evaluation can provide a quantifiable impact score, which reflects the degree to which the species might negatively affect the ecosystem, human activities, or both.

The results of a GLANSIS organism impact assessment can be used guide management decisions, such as prevention strategies, control measures, and research directions, by highlighting invasive species that may have particularly significant impacts on the Great Lakes ecosystem. Rankings of the top ten most harmful ANS can serve as a reference point for researchers, educators and communicators as the Great Lakes continue to be affected by the spread of invasive species.

GLANSIS (The Great Lakes Aquatic Nonindigenous Species Information System) is dedicated to tracking sightings and impacts of introduced species throughout the whole Great Lakes basin. The GLANSIS team analyzed the impacts of the nearly 200 non-native species reported in the region to figure out what traits and impacts they have in common, and which caused the worst problems for the environment and the economy. This StoryMap is designed to be an interactive companion piece to the resulting research paper, which can be read here:  The Great Lakes’ most unwanted: Characterizing the impacts of the top ten Great Lakes aquatic invasive species . 

So, which species are the most impactful invaders in the Great Lakes? Read on to find out!

• Range: The white perch (Morone americana) is found in the Great Lakes region, though it is native to the Atlantic coastal waters of North America. It has adapted to various freshwater and brackish environments.
• Preferred Habitat: Typically found in shallow estuaries, rivers, and lagoons, but can also thrive in deeper waters and lakes. They prefer slower-moving or still water with moderate vegetation.
• Diet: White perch are opportunistic feeders with a varied diet that includes small fish, crustaceans, insects, and zooplankton. Their flexible diet allows them to adapt and thrive in a variety of ecological niches.
• Behavior: Known for their adaptability, white perch can survive in a range of salinities and temperatures. They are a schooling species, often found in large groups.
• Reproduction: They have high reproductive rates, with spawning occurring in shallow waters in the spring. Fertilized eggs are left to drift and develop in open water, leading to high juvenile survival rates, contributing to their rapid population growth.

• Competition: White perch can outcompete native species for food and habitat, which can lead to declines in native fish populations. Their diet overlaps with that of native species, including young sport fish, potentially disrupting local food webs.
• Genetic: White perch can hybridize with native species like the white bass Morone chrysops and yellow perch Morone mississippiensis (Irons et al. 2002). This genetic mixing can impact the genetic integrity of native populations and may lead to the production of less healthy hybrids, affecting population stability and diversity.
• Predation: As an opportunistic feeder, white perch prey on the eggs and larvae of other fish species, which can decrease the reproductive success of native fish and further disrupt ecosystem balance.

• Commerce and Recreation: White perch can negatively impact commercially and recreationally important fish species by outcompeting them for food and habitat and preying on their eggs and larvae. This can lead to declines in populations of sought-after species like walleye and yellow perch, potentially reducing catches for both commercial and recreational fishers and affecting local fisheries' profitability and sustainability. The collapse of a walleye fishery in the Bay of Quinte, Lake Ontario is attributed to egg predation by white perch (Schaeffer and Margraf 1987).

• Range: The round goby (Neogobius melanostomus) inhabits the Great Lakes region, having originated from the Black and Caspian Seas in Eastern Europe. It thrives in a variety of aquatic environments, including lakes, rivers, and coastal areas.
• Preferred Habitat: Prefers rocky and sandy substrates and is commonly found in shallow waters, though it can adapt to deeper environments. They are known for their ability to survive in a range of environmental conditions, including areas with low oxygen levels.
• Diet: Round gobies are opportunistic feeders, primarily consuming benthic invertebrates such as mussels, crustaceans, insects, and small fish. Their diet can include the eggs and larvae of native fish species, making them aggressive competitors in their new environments.
• Behavior: They are known for their aggressive behavior and high reproductive rates, which contribute to their rapid spread and establishment in new areas. They often outcompete native species for food and habitat.
• Reproduction: They have a prolific reproductive strategy, spawning multiple times from April to September. Males establish and defend nests in rocky or sheltered areas, where females lay adhesive eggs. Each female can produce several hundred eggs per spawning. Males guard the eggs until they hatch, ensuring high survival rates.

• Competition: Round gobies compete with native fish species, such as sculpins and darters, for food and habitat. This competition can lead to declines in native fish populations. In Lake Michigan for example, Round goby impacts survival of deepwater sculpins (Myoxocephalus thompsonii) through competition for Mysis, a limited prey item (Jude et al. 2022).
• Predation: They prey on the eggs and young of native species, including sport fish like smallmouth bass and walleye, negatively affecting the reproductive success and population stability of these native species.
• Habitat Alteration: By preying on invasive zebra and quagga mussels, round gobies can indirectly influence the ecosystem. While they help control these mussel populations, this also leads to changes in nutrient cycling and water clarity.
• Food Web: Their presence can lead to trophic cascades, altering food webs and the structure of aquatic communities. This can have far-reaching impacts on the ecosystem, including changes in the abundance and diversity of species.

• Commerce: Round gobies compete with and prey on native fish species, including those valuable to commercial fisheries such as smallmouth bass, walleye, and lake trout. This competition and predation can lead to declines in these economically important fish populations, affecting the catch rates and economic returns for both commercial fishers. While round gobies themselves are sometimes used as bait, their presence can negatively impact the availability of more traditionally valued bait species, impacting the bait industry.
• Recreation: Reduced populations of native sport fish can decrease recreational fishing opportunities, which are an important cultural and economic activity for local communities. This can lead to a decline in tourism and associated revenues, negatively affecting local economies. Beginning in 2004, the State of Ohio has closed the smallmouth bass Micropterus dolomieu fishery in Lake Erie during the months of May and June, due to high predation rates by round goby on nests affecting recruitment (National Invasive Species Council 2004).
• Aesthetic and Cultural Significance: Many communities in the Great Lakes region have cultural ties to native fish species. The decline of these species due to round goby predation and competition can have negative cultural and social impacts, affecting community traditions and heritage.

• Range: Common reed (Phragmites australis) is widely distributed in the Great Lakes region and other parts of North America. It thrives in wetlands, including marshes, riverbanks, lake shores, and roadside ditches.
• Preferred Habitat: Prefers moist, nutrient-rich environments with fluctuating water levels. It can tolerate various conditions, from fresh to brackish water.
• Growth: Common reed is a perennial grass that grows in dense stands, often forming monocultures that crowd out native plants. It spreads through both seeds and rhizomes (underground stems).
• Behavior: Known for its aggressive growth and ability to alter habitats, common reed can reach heights of up to 4 meters (13 feet). Its dense growth patterns reduce light penetration and alter the soil composition, making it challenging for native plants to survive.

• Competition: The dense monocultures formed by common reed displace native plant species, leading to reduced plant diversity. This loss of native flora can affect entire ecosystems, including insects, birds, and fish that depend on native vegetation for food and habitat.
• Habitat Alteration: Common reed can change local hydrology by increasing evapotranspiration rates and trapping sediments, leading to altered water flow. This can affect wetland hydrology and reduce water availability for other species.
• Water Quality: The plant can alter soil chemistry by increasing soil salinity and reducing nutrient availability, further degrading habitats for native plants and animals.
• Ecosystem Function: The displacement of native plants and alteration of hydrology and soil chemistry can lead to changes in ecosystem functions, such as nutrient cycling and primary production. When meadow marshes were replaced with Phragmites in Long Point peninsula, Ontario, Canada, the stocks of calcium, phosphorus, potassium, nitrogen, magnesium, and carbon all increased significantly (Yickin and Rooney 2019).

• Management and Control Costs: Controlling and managing common reed infestations require significant financial resources, including herbicide applications, mechanical removal, and ongoing monitoring. These efforts are costly for local governments, conservation organizations, and private landowners.
• Commerce and Infrastructure: Dense stands of common reed can obstruct drainage systems, leading to waterlogged agricultural lands and blocked culverts and ditches. This can cause increased maintenance costs and potential agricultural losses. Additionally, dense stands of invasive Phragmites impede shore access and restrict the shoreline view which can reduce property values (Avers et al. 2014).
• Recreation and Aesthetic: The invasion of common reed in wetlands and shorelines can reduce recreational opportunities such as birdwatching, fishing, and boating. The monocultures are often considered less visually appealing compared to diverse native plant communities, which can decrease the aesthetic value of natural areas.
• Ecosystem Services: The overall reduction in biodiversity and alteration of ecosystem functions can impact ecosystem services that provide economic benefits, such as water purification, flood control, and habitat for commercially important fish and wildlife species.

• Range: Water chestnut (Trapa natans) is an invasive aquatic plant in the Great Lakes region. It is native to Europe, Asia, and Africa but has spread to North American waterways.
• Preferred Habitat: Typically found in slow-moving, nutrient-rich freshwater environments such as ponds, lakes, rivers, and shallow bays. Prefers waters with a depth range of 0.5 to 4 meters (1.6 to 13 feet).
• Growth: Water chestnut is an annual aquatic plant that forms dense floating mats of vegetation. It grows rapidly, with each plant producing hundreds of rosettes that can cover extensive water surfaces.
• Behavior: The plant spreads through its hard, spiky fruits, which can remain viable for up to 12 years. It anchors itself in the sediment with a long, flexible stem and can quickly dominate water surfaces, shading out other aquatic plants and disrupting local ecosystems.

• Competition: The dense mats formed by water chestnut block sunlight from reaching underwater plants, leading to reduced photosynthesis and declines in native aquatic flora (Naylor 2003).
• Food Web: Reduction in plant diversity can affect the entire aquatic food web, including fish and invertebrate species that depend on native plants for food and habitat.
• Water Quality: The dense growth can reduce water flow and increase sedimentation, leading to decreased oxygen levels in the water. This can create hypoxic conditions (low oxygen levels) detrimental to fish and other aquatic organisms.
• Habitat Alteration: By altering water flow and light availability, water chestnut can change ecosystem dynamics and reduce the overall health and functionality of aquatic ecosystems. Decreased plant diversity and lower oxygen levels can have cascading effects on water quality and habitat suitability.

• Management and Control Costs: Controlling water chestnut infestations requires significant financial investment. Efforts include mechanical harvesting, manual removal, and the use of herbicides. These control methods are labor-intensive and costly for local governments, environmental agencies, and private stakeholders.
• Recreation and Commerce: Dense mats of water chestnut can impede boating, fishing, and swimming, reducing recreational opportunities and associated tourism revenue. The plant's presence can also interfere with commercial fishing operations and affect the aesthetics of water bodies, making them less appealing for residents and visitors. It is suspected that dense beds of Trapa natans played a role in the drowning deaths in the Hudson River in 2001 by entangling swimmers (Hummel and Kiviat 2004).
• Infrastructure: The invasive growth can clog water intakes, irrigation systems, and drainage infrastructure, leading to increased maintenance costs and potential disruptions in water management systems.
• Ecosystem Services: The presence of water chestnut can reduce ecosystem services provided by healthy aquatic ecosystems, such as water purification, flood control, and habitat for economically important fish and wildlife species. These services have direct and indirect economic benefits for communities.

• Range: Grass carp (Ctenopharyngodon idella) is native to large rivers and lakes in East Asia but has been introduced in the Great Lakes region and other parts of North America.
• Preferred Habitat: Prefers slow-moving or still bodies of water such as lakes, ponds, rivers, and reservoirs. Grass carp thrive in a variety of aquatic habitats as long as there is abundant submerged vegetation.
• Diet: Grass carp are herbivorous and primarily feed on submerged aquatic vegetation. They can consume large amounts of plant material, greatly reducing aquatic plant biomass.
• Behavior: Known for their rapid growth and high reproductive potential, grass carp can reach considerable sizes. They are often introduced for biological control of aquatic vegetation but can establish wild populations if not properly managed.
• Reproduction: They reproduce in late spring and early summer in flowing rivers. Females release hundreds of thousands of eggs, which are fertilized by males and drift downstream. The eggs hatch into larvae within days, promoting rapid population growth.

• Herbivory: Grass carp significantly reduce aquatic plant populations due to their high consumption rates. This can lead to loss of habitat and food sources for various aquatic species, including fish and invertebrates.
• Food Web: The removal of aquatic vegetation by grass carp can lead to declines in biodiversity. Aquatic plants provide essential habitat and spawning grounds for many native species, and their loss can negatively impact these populations.
• Water Quality: The reduction of vegetation can lead to increased water turbidity and nutrient levels, resulting in algal blooms and decreased water quality (Maceina et al. 1992). This can create unfavorable conditions for many aquatic organisms.
• Habitat Alteration: By altering plant communities and water quality, grass carp can disrupt ecosystem functions such as nutrient cycling, sediment stabilization, and the provision of habitat and food for other species.

• Management and Control Costs: Managing grass carp populations involves costs associated with monitoring, research, and implementing control measures. Preventing their spread and mitigating their impacts requires ongoing financial investment from local governments and environmental agencies.
• Commerce: The decline in aquatic vegetation can negatively impact fisheries by reducing habitat for fish and other aquatic life. This can lead to declines in commercially and recreationally important fish populations (Petr and Mitrofanov 1998), affecting both commercial operations and recreational fishing opportunities.
• Recreation: The degradation of water quality and the reduction of aquatic vegetation can impact recreational activities such as boating, swimming, and fishing. This can lead to decreased tourism revenue and reduced enjoyment of natural water bodies by residents and visitors.
• Ecosystem Services: The loss of aquatic vegetation and the resulting environmental changes can reduce ecosystem services provided by healthy aquatic ecosystems. This includes water purification, flood control, and habitat for pollinators, all of which have direct and indirect economic benefits.

• Range: Japanese stiltgrass (Microstegium vimineum) is native to East Asia but has become an invasive species in the Great Lakes region and other parts of North America.
• Preferred Habitat: It thrives in a variety of habitats, including forest understories, wetlands, stream banks, roadsides, meadows, and disturbed areas. It prefers shaded, moist environments but can also tolerate a range of light and moisture conditions.
• Growth: Japanese stiltgrass is an annual grass that spreads rapidly, forming dense mats that can outcompete native vegetation. It reproduces both by seeds and stolons (horizontal stems that root at nodes).
• Behavior: The species has a high reproductive rate, producing a significant number of seeds that can remain viable in the soil for several years. Its ability to grow in dense mats enables it to dominate large areas quickly.

• Competition: The dense mats formed by Japanese stiltgrass crowd out native plants, leading to reduced biodiversity (Leicht et al 2005). This displacement of native flora can affect entire ecosystems, including insects, birds, and other wildlife that depend on native plants for food and habitat.
• Habitat Alteration: Japanese stiltgrass can alter soil chemistry, particularly by increasing nitrogen cycling rates. This change can disadvantage native species adapted to lower nitrogen levels and further facilitate the spread of the stiltgrass. The accumulation of its dry biomass in the fall can alter fire regimes, increasing the likelihood of wildfires and affecting native plant and animal communities.

• Management and Control Costs: Controlling Japanese stiltgrass infestations requires significant financial resources and labor (Flory 2017). Mechanical removal, herbicide application, and ongoing monitoring are necessary to manage its spread. These efforts are costly for land managers, conservation organizations, and governmental agencies.
• Commerce: Its spread into agricultural lands can interfere with crop production, leading to economic losses for farmers. Dense growth can compete with crops for resources such as nutrients, water, and light. In forested areas, stiltgrass can impede forest regeneration by outcompeting young tree seedlings, potentially impacting timber yields and forest health (Flory and Clay 2010).
• Recreation and Aesthetic: The invasion of Japanese stiltgrass can reduce the recreational value of natural areas such as parks, trails, and preserves by altering their aesthetic and ecological integrity. This can negatively impact tourism and local economies dependent on outdoor recreational activities.
• Ecosystem Services: The reduction in native biodiversity and habitat quality can impair ecosystem services such as soil stabilization, water filtration, and carbon sequestration, which have direct and indirect economic benefits for human communities.

• Range: Sea lamprey (Petromyzon marinus) are native to the Atlantic Ocean but have invaded the Great Lakes region. They occupy a variety of aquatic habitats, including lakes, rivers, and streams.
• Preferred Habitat: They prefer clean, well-oxygenated waters for spawning and larval development. Spawning typically occurs in gravelly stream beds, while larvae (ammocoetes) burrow into soft sediment in calm, nutrient-rich freshwater environments.
• Diet: Adult sea lampreys are parasitic, feeding on the blood and body fluids of fish. They attach to their hosts using a suction-cup-like mouth lined with sharp teeth and a rasping tongue.
• Reproduction: Sea lampreys have a complex life cycle that includes a larval stage in freshwater streams, a parasitic adult stage in larger bodies of water, and a migratory spawning stage where adults return to freshwater streams to reproduce.

• Predation: Sea lampreys are highly effective predators that significantly impact fish populations by preying on a variety of fish species, including economically important ones like lake trout, salmon, and whitefish. This predation leads to decreased survival and reproduction rates for host fish.
• Food Web: The heavy predation pressure exerted by sea lampreys can lead to declines in native fish populations, reducing biodiversity and altering fish community structures. The decline in top predator fish species due to sea lamprey predation can result in trophic cascades, affecting the entire aquatic food web and leading to broader ecosystem imbalances. In the Great Lakes, for example, the reduction in top predators as a result of sea lamprey invasion caused alewife populations to boom, leading to fish die-offs (Smith and Tibbles 1980).

• Commerce and Recreation: The significant reduction in populations of economically valuable fish species due to sea lamprey predation has a direct negative impact on commercial and recreational fisheries. This leads to decreased fish catches, reduced income for fishers, and economic losses for communities reliant on fishing industries. This is especially prevalent in the Great Lakes region, where sea lamprey has 'devastated' the fishing industry (Dochoda 1988).
• Management and Control Costs: Extensive resources are allocated to sea lamprey control programs, including the use of lampricides, barriers, traps, and sterile-male release techniques. These management efforts are necessary but costly, requiring continuous financial investment from government agencies and conservation organizations.
• Research and Monitoring: Ongoing research and monitoring efforts to understand sea lamprey population dynamics and develop new control methods further contribute to the financial burden on managing agencies.
• Recreation and Tourism: Declines in native fish populations can affect recreational fishing opportunities, diminishing the appeal of the Great Lakes for anglers and impacting tourism revenue.
• Ecological Restoration: Efforts to restore fish populations and ecosystems impacted by sea lampreys involve additional costs, further straining conservation budgets and resources.

• Range: Alewife (Alosa pseudoharengus) are native to the Atlantic coast of North America but have established invasive populations in the Great Lakes region.
• Preferred Habitat: They inhabit a variety of aquatic environments, including lakes, rivers, and coastal areas. Alewives are anadromous, typically living in larger bodies of water and migrating to freshwater rivers and streams for spawning.
• Diet: Alewives are primarily planktivorous, feeding on zooplankton, but they also consume small fish and invertebrates. Their feeding behavior can affect the availability of prey for other fish species.
• Behavior: Alewives form large schools, which offer protection from predators and improve foraging efficiency. They migrate to freshwater sources to spawn in the spring. 
• Reproduction: Alewives have a complex life cycle that involves spawning in freshwater habitats. Adults migrate from larger bodies of water to rivers and streams to spawn, and the juveniles eventually make their way back to larger water bodies where they grow and mature.

• Competition and Predation: Alewives compete with native fish species for food, particularly zooplankton, which can lead to declines in native fish populations. They also prey on the eggs and larvae of native species, further impacting their recruitment and survival.
• Food Web: The presence of alewives can lead to shifts in zooplankton communities and reductions in native fish populations (Eck and Wells 1987), affecting overall biodiversity within the ecosystem. By heavily consuming zooplankton, alewives can reduce the food availability for other fish species, potentially leading to trophic cascades that alter the structure and function of the aquatic ecosystem. This can affect nutrient cycling and energy flow within the ecosystem.
• Impact on Salmonids: Alewives contain high levels of thiaminase, an enzyme that breaks down thiamine (vitamin B1). Predatory fish that feed on alewives, such as salmon and trout, can suffer from thiamine deficiency, leading to poor health and reduced reproductive success (Fitzsimons et al. 1999).

• Impact on Fisheries: The competition and predation by alewives can negatively impact populations of commercially and recreationally important fish species such as salmon, trout, and perch (Madenjian et al. 2008). This can lead to decreased fish catches, reduced income for commercial fishers, and economic losses for communities reliant on fishing industries.
• Management and Mitigation Costs: Managing the impacts of alewives involves significant financial resources. This includes efforts to control their numbers, restore affected fish populations, and address the issue of thiamine deficiency in predatory fish.
• Research and Monitoring: Ongoing research and monitoring are necessary to understand the population dynamics of alewives and their impacts on the ecosystem. These efforts require continuous investment from governmental and environmental organizations.
• Recreational and Tourism Impacts: Reduced populations of native sport fish due to alewife competition and predation can diminish recreational fishing opportunities, impacting tourism revenue and the economy of local communities.
• Ecosystem Restoration: Efforts to restore native fish populations and improve ecosystem health involve additional costs, further straining conservation budgets and resources.

• Range: Quagga mussels (Dreissena bugensis) are native to the Dnieper River drainage of Ukraine but have spread to the Great Lakes region through ballast water discharge from ships.
• Preferred Habitat: They inhabit a wide variety of freshwater habitats, including lakes, rivers, and reservoirs. Quagga mussels can colonize substrates at various depths and can tolerate a range of temperatures and water conditions.
• Diet: Quagga mussels are filter feeders, consuming phytoplankton, zooplankton, and organic particles suspended in the water. This feeding behavior significantly impacts the availability of food resources for other aquatic organisms.
• Reproduction: They have a high reproductive rate and can produce large numbers of offspring. The planktonic larvae, called veligers, allow for wide dispersal and rapid population growth.

• Habitat Alteration: Quagga mussels are considered "ecosystem engineers" because they significantly alter aquatic habitats. Their filter-feeding activity increases water clarity but removes large amounts of plankton, disrupting local food webs. Quagga mussels attach to various surfaces, including rocks, docks, boats, and water intake structures, forming dense colonies that can alter the physical characteristics of aquatic habitats.
• Competition: By outcompeting native bivalves and altering the availability of food resources, quagga mussels contribute to declines in native species populations (Ricciardi 2001). They also create hard surfaces that facilitate colonization by other invasive species.
• Water Quality and Nutrient Cycling: Their filtering activity influences nutrient dynamics (Vanni 2021), often leading to the accumulation of organic material on the lakebed. This can create hypoxic (low-oxygen) conditions, affecting benthic (bottom-dwelling) organisms.

• Infrastructure: Quagga mussels fouls water intake pipes, power plants, and other industrial infrastructure, causing significant damage and leading to increased maintenance and cleaning costs. This can disrupt water treatment and power generation, leading to economic losses.
• Management and Control Costs: Efforts to manage and control quagga mussel populations require substantial financial resources. Methods include mechanical removal, chemical treatments, and ongoing monitoring programs, all of which are expensive to implement and maintain.
• Commerce and Recreation: Changes in food web dynamics due to quagga mussel populations can affect the abundance and health of commercial and recreational fish species (Fahnenstiel et al. 2010). This impacts commercial fisheries and reduces recreational fishing opportunities, leading to economic losses for communities reliant on these industries.
• Water Quality: While increased water clarity might seem beneficial, the resulting environmental changes, such as nutrient buildup and hypoxic conditions, can negatively impact water quality (Evans et al. 2011). This affects recreational activities such as swimming and boating and can lead to decreased tourism revenue.
• Research and Restoration: Addressing the impacts of quagga mussels involves ongoing research and ecosystem restoration efforts. These activities require continuous investment and resources from governmental agencies and environmental organizations.

• Range: Zebra mussels (Dreissena polymorpha) are native to the freshwater lakes of southeastern Russia and Ukraine but have become widespread in the Great Lakes and other North American waterways, primarily through ballast water discharge from ships.
• Preferred Habitat: Zebra mussels thrive in a variety of freshwater habitats, including lakes, rivers, reservoirs, and canals. They prefer hard substrates like rocks, metal, and wood, but can also colonize softer substrates like sandy or muddy bottoms if no other options are available.
• Diet: Zebra mussels are filter feeders, consuming phytoplankton, zooplankton, and suspended organic particles in the water. Their high filtration capacity can significantly reduce the availability of plankton for other aquatic organisms.
• Reproduction: They have a high reproductive rate, with a single female capable of producing up to one million eggs per season. Their veliger larvae are planktonic, contributing to their wide dispersal and rapid population growth.

• Habitat Alteration: Zebra mussels profoundly alter aquatic ecosystems through their filter-feeding activity, which increases water clarity but depletes plankton populations, affecting the entire food web. Zebra mussels attach to a variety of surfaces, forming dense colonies that can clog water intake structures, cover native species, and alter the physical characteristics of aquatic habitats.
• Food Web: They outcompete native bivalves and other filter feeders, leading to declines in native species populations. Zebra mussels also create hard surfaces that encourage the establishment of other invasive species.
• Water Quality and Nutrient Cycling: Their filtration can lead to increased sedimentation of organic material on the lake or riverbed, contributing to hypoxic conditions that harm benthic organisms. Changes in nutrient dynamics can also result in algal blooms and other water quality issues. For instance, the zebra mussel infestation completely changed the water quality of the Oswego River. Prior to the mussel's arrival the river was turbid and phytoplankton-rich. After the arrival, turbidity decreased and phytoplankton concentrations were reduced (Effler and Siegfried 1998).

• Infrastructure: Zebra mussels cause significant fouling of water intake pipes, power plants, industrial facilities, and municipal water supplies. The associated maintenance and cleaning costs to mitigate these impacts are substantial. Disruptions in water treatment and power generation can lead to economic losses.
• Management and Control Costs: Efforts to manage zebra mussel populations, including mechanical removal, chemical treatments, and ongoing monitoring, require considerable financial resources. These efforts are expensive and must be sustained over the long term.
• Commerce and Recreation: By disrupting the food web and outcompeting native species, zebra mussels can affect the populations of commercially valuable fish. Reduced fish stocks negatively impact commercial and recreational fisheries, leading to economic losses for communities reliant on these industries. Additionally, accumulation of dead zebra mussel shells at beaches and along shorelines can negatively impact the aesthetic and recreational value of invaded areas (Mackie 1991).
• Water Quality: While increased water clarity may be perceived as positive, the accompanying environmental changes—such as increased sedimentation and hypoxic conditions—can degrade overall water quality. This affects recreational activities like swimming and boating and can lead to decreased tourism revenue. Residents and business owners on Lake Ontario have attributed decreases in revenue or property values to excessive blooms of Cladophora following zebra mussel invasion (Limburg et al. 2010).
• Research and Restoration: Addressing the impacts of zebra mussels involves ongoing research, ecosystem restoration efforts, and public education campaigns. These activities necessitate continuous investment and resources from governmental agencies, researchers, and environmental organizations.

• The most impactful species tend to be fish from Eurasia, introduced via ballast water.
• There is no clear-cut profile for invasive species, as their life histories and ecological effects vary significantly.

• Common impacts among the top ten species include altering predator/prey dynamics, posing threats to native species, outcompeting natives, affecting recreation, economy, and aesthetics.
• The analysis shows diverse impact types and emphasizes that high-impact species cause system-wide disruptions rather than isolated issues.

• Invasive species cause extensive ecological damage, including food web alterations and acting as ecosystem engineers.
• They also have significant socio-economic impacts by impeding recreational and commercial activities and requiring costly management.

• Continual early detection and rapid response efforts are crucial to managing new and existing invasive species.
• Cross-taxa assessments can prioritize management efforts more effectively.

• The rankings may evolve over time as new information emerges.
• Consideration of invasive species' behavior and impact history in other regions can improve risk assessments.
• Knowledge gaps, particularly from non-English literature, need addressing for comprehensive understanding.

• Understanding the complex effects of invasive species improves conservation, management, and restoration efforts in the Great Lakes.
• The study's findings are intended to support both practical management strategies and educational initiatives.

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Dochoda, M. 1988. Fact sheet on the transport and control of exotic biota introduced into the Great Lakes through ship ballast water. Great Lakes Fishery Commission.

Effler, S.W., and C. Siegfried. 1998. Tributary water quality feedback from the spread of zebra mussels: Oswego River, New York. Journal of Great Lakes Research 24(2):453-463.

Evans, M.A., G. Fahnenstiel, and D. Scavia. 2011. Incidental oligotrophication of North American Great Lakes. Environmental Science & Technology 45:3297-3303.

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