Invasive species are non-native plants and animals whose presence degrades habitat, outcompetes native species, and decimates the food web. Humans, animals, and various modes of transportation and interconnecting pathways (i.e. rivers) introduce them to the environment. The Great Lakes are susceptible to invasive species, with ocean freight transportation being a major contributor. Sixty-five percent of the invasive species in the Great Lakes arrived through the discharge of ballast water from these ocean-going freighters. Another major source of invasive species entering the Great Lakes has been through canals and waterways. There are more than 180 known invasive species in the Great Lakes.
Asian Carp
The biggest invasive species threat on the Great Lakes may be Asian Carp, which would massively disrupt the food chain in the Great Lakes. Asian carp species that pose a significant threat to the freshwater aquatic environment are bighead carp, silver carp, and grass carp.
Government agencies intentionally introduced bighead, silver and grass carp in the Mississippi River basin to control nuisance algae blooms and aquatic vegetation in aquaculture facilities, farm ponds and sewage lagoons. Black carp were introduced to control a parasite-hosting snail commonly found in aquaculture facilities. But floods helped carp escape from private ponds and aquaculture facilities and human activities such as live bait releases, intentional stocking (to create a food source), and the construction of man‐made canals helped these fishy fugitives on their path to freedom.
Once loose, Asian carp spread quickly, reproduce rapidly, and became abundant. Depending on its size, a female Asian carp can produce up to a million eggs each year.
Should Asian Carp enter the Great Lakes, the economic cost for fisheries alone is estimated at $7 billion per year. The fish will likely enter Lake Michigan via the Chicago River or other waterways connected to the Mississippi watershed.
The introduction of invasive species via canals and waterways is complex, and the Asian Carp threat brings these issues to light. There are 18 points along the Great Lakes Basin and the Mississippi Basin that pose risks where Asian Carp and other species could potentially enter into the Great Lakes. Among the highest risks is the Chicago River in Illinois. The Chicago River was reversed at the turn of the century to flush Chicago’s sewage through the canals, the Des Plaines River, and eventually to the Mississippi River. The long-anticipated Great Lakes and Mississippi River Interbasin Study was released in 2015 by the U.S. Army Corps of Engineers. The study affirmed the feasibility of the hydroseparation of the Great Lakes and Mississippi River Basins to restore the continental divide and prevent further transfer of invasive species, but the project was estimated to cost over $18 billion and would take 25 years to complete.
In the summer of 2018, Congress is debating deadline for a study looking at ways to prevent Asian carp from entering the Great Lakes. The Brandon Road Study aims to evaluate options and technologies near the Brandon Road Lock and Dam site in Joliet, Ill., to prevent aquatic invasive species from reaching the Great Lakes. The study is seen by supporters as key to developing strategies to keep Asian Carp out.
Zebra and Quagga Mussels
Quagga and zebra mussels are native to Eastern Europe and arrived in the Great Lakes after being transported in ballast water. Zebra mussels first appeared in Lake St. Clair in 1986. Quagga mussels first arrived in the Great Lakes in 1989. Both mussel species are small and typically grow to the size of a fingernail. They are prolific breeders and can attach to both hard and soft surfaces in freshwater ways.
Quagga and zebra mussel invasions clog water intake structures (e.g., pipes and screens), increasing maintenance costs for water treatment and power plants. Mussels accumulate on docks, buoys, boat hulls, anchors, and beaches can become heavily encrusted.
Zebra and quagga mussels can kill native freshwater mussels in two ways:
- Attaching to the shells of native species, and
- Outcompeting native mussels and other filter feeding invertebrates for food.
The encrusting of lake and river bottoms can displace native aquatic arthropods that need soft sediments for burrowing. This has led to the collapse of amphipod populations that fish rely on for food and the health of fish populations has been severely affected.
The invasive mussels have been associated with avian botulism outbreaks in the Great Lakes and the death of tens of thousands of birds. Because of their filter feeding habit, it has been estimated that these mussels can bioaccumulate organic pollutants in their tissues by as much as 300,000 times when compared to concentrations in the water in which they are living. Consequently, these pollutants can biomagnify as they are passed up the food chain. High mussel populations can increase water acidity and decrease concentrations of dissolved oxygen.
In 2010, the National Oceanic and Atmospheric Administration estimated that there were 437 trillion quagga mussels in Lake Michigan alone. This spring scientists reported a “continuous carpet” of quagga mussels from one shore of Lake Michigan to the other.
Quagga mussels have consumed a majority of the vegetation on southern Lake Michigan bottomlands, and reduced the biomass of Lake Huron by 95%, resulting in the closure of several commercial fisheries and charters.
The quagga mussel is also a contributor to the massive algal blooms occurring on Lake Erie and in other areas of the Great Lakes. Although the mussels actually clean the water, this allows sunlight to penetrate deeper, creating perfect conditions for algae to grow and take over the ecosystem, especially combined with nutrient runoff.
Sea Lamprey
Sea lamprey are parasitic fish native to the Atlantic Ocean. Sea lamprey, which parasitize other fish by sucking their blood and other body fluids, have remained largely unchanged for more than 340 million years and have survived through at least four major extinction events.
The sea lamprey entered the Great Lakes through the Welland Canal in 1921, and since then has been decimating key predator and game fish like lake trout, lake whitefish, chub, and lake herring. The species played a large role in the destruction of the Lake Superior lake trout population. The lamprey has an advantage by parasitizing these native species, who had previously faced no predators in the native Great Lakes ecosystem.
Before the sea lamprey invasion, Canada and the United States harvested about 15 million pounds of lake trout in the upper Great Lakes each year. By the late 1940s, sea lamprey fed on large numbers of lake trout, lake whitefish, and ciscoes—fish that were the mainstays of a thriving Great Lakes fishery. By the early 1960s, the catch had dropped dramatically, to approximately 300,000 pounds, about 2% of the previous average. During the time of highest sea lamprey abundance, up to 85% of fish not killed by sea lampreys were marked with sea lamprey attack wounds.
The Great Lakes Fishery Commission administers a control program that relies on exploiting sea lamprey vulnerability when they are congregated in Great Lakes tributaries, at either the larval or adult stages of their life cycle. Pesticides selective to lampreys are deployed to kill larval sea lampreys in the tributaries, while a combination of barriers and traps are used to prevent the upstream migration and reproduction of adult sea lampreys.
