I’m reading about the Great Lakes in preparation for a cruise on the Great Lakes from Chicago to Toronto. (1,2) It’s a story of continuous invasions of aquatic creatures, one after the other, with many more expected in the future. Every one of those invasions was caused by the removal of natural barriers from isolated bodies of water to accommodate human activities such as shipping of goods.
Connecting the Great Lakes to the Atlantic Ocean
The St. Lawrence River is the natural gateway into the Great Lakes from the Atlantic Ocean. The salty water of the ocean and the fresh water of the lakes was part of the natural barrier that protected the lakes from invasive species because, for the most part, the marine creatures that live in salty water are different from those that live in fresh water.
The St. Lawrence River was steep and narrow, creating white-water rapids that limited travel from the ocean to the lakes (or vice versa) in anything but a birch bark canoe that could be carried around the rapids. The natural barrier was penetrated by building the St. Lawrence Seaway in 1959 that widened the river and used locks to climb the steep incline of the river into Lake Ontario.
The St. Lawrence Seaway was instantly obsolete because of the unforeseen container revolution that transformed global shipping. The transition from traditional to container shipping was instantaneous because the advantages are so great. Container ships are huge in comparison to the small ships that had been loaded by hand for centuries. The St. Lawrence Seaway is too narrow to accommodate container ships. The loans given to the builders of the seaway by Canada and the US were eventually forgiven because the tolls on the seaway will never pay for the expense.
But the damage was done, although much of it could have been avoided. The ships that start their voyage in fresh water ports on rivers take on their ballast water when they start their voyage and with it freshwater aquatic creatures that don’t live in the Great Lakes. When they arrive in the Great Lakes they dump their ballast water to take on their cargo. The dumping of ballast water in the Great Lakes could have been regulated in 1959, but it wasn’t. Only very recently have ships from fresh water ports been asked to exchange their ballast water in the ocean, before entering the Great Lakes and those regulations weren’t mandatory until 2021. Such is the power of commercial interests that the consequences of introducing new species into the Great Lakes were not considered.
The second natural barrier that protected the Great Lakes was Niagara Falls in New York with a vertical drop of 160 feet. That steep cliff across the Niagara River prevented the movement of marine animals from the Atlantic Ocean, through Lake Ontario and into the other four lakes. It was one of the first barriers to be penetrated by the Erie Canal in 1825 and the Welland Canal in 1829. The Erie Canal connects the Hudson River that flows into the Atlantic Ocean to Lake Erie, bypassing Niagara Falls and creating a gateway from the Atlantic Ocean into the Great Lakes. The Welland Canal connects Lake Ontario to Lake Erie, which also bypassed Niagara Falls and created another gateway from the Atlantic Ocean to all of the Great Lakes.
Connecting the Great Lakes to the Mississippi River Basin
The St. Lawrence Seaway, Erie, and Welland canals opened the front door of the Great Lakes to salt water creatures in the Atlantic Ocean and the ships that brought foreign aquatic animals into the Great Lakes. The reversal of the Chicago River that connected Lake Michigan to the entire Mississippi River basin, opened the back door to the Great Lakes to all of the freshwater aquatic animals that live in the vast Mississippi River basin, east of the Continental Divide.
When Chicago was built, it dumped its sewage into Lake Michigan and it also took its drinking water from Lake Michigan. As the population of Chicago grew it became more vulnerable to typhoid epidemics caused by the polluted water Chicago was drinking. The Chicago River had sent a dribble of water into Lake Michigan from its headwaters not far west of Chicago before it was reengineered.
In 1900, Chicago built a huge sanitary canal that connected Lake Michigan to the Mississippi River. The sanitary canal carried Chicago’s sewage into the Mississippi River and created a shipping lane to the Mississippi River while giving Chicago a clean source of water from Lake Michigan. The sanitary canal reversed the flow of the Chicago River, which now flows out of Lake Michigan.
The Consequences
The first invasive predator of native fish arrived in the Great Lakes via the canals built early in the 19th century. The sea lamprey is a parasite that attaches itself to the bellies of fish and slowly sucks the blood out of it. Its suction-cup mouth is the stuff of nightmares.
Lampreys, like salmon and sturgeon, are born in freshwater rivers and streams before living in the ocean and finally returning to their freshwater birth place to spawn and die. They are capable of living in both fresh and salty water. In the Great Lakes lampreys did not need to migrate to the ocean as their ancestors had because there was sufficient food in the lakes.
As late as the 1940s commercial fishermen in the Great Lakes were harvesting 100 million pounds of native fish, such as lake trout and whitefish, annually. Lampreys were first reported in Lake Michigan in 1936. By 1950, the commercial fishery had all but collapsed as the lamprey population reached its peak.
Lampreys met their match when a graduate student at University of Michigan wrote his Ph.D. thesis about the life cycle of lampreys. He spent several years stalking lampreys in Lake Michigan and its tributaries, finding out where and when they spawn and at what point in their life cycle they become parasites of fish.
The lamprey population had been so vast that it was impossible to target an attack on them. An understanding of their life cycle enabled the development of a strategy to eradicate them. More than 5 of their 7-year lifespan is spent burrowed in the gravel of small streams that feed into the lakes. At that stage they are not yet fish predators.
Armed with the knowledge of when and where lampreys were most vulnerable, the strategy was to build mesh barriers that prevented the lampreys from returning to the streams to spawn. There was some success with the barriers, but not sufficient to reduce the huge population.
The final solution to lamprey control was the use of a chemical that would poison lampreys without killing native fish. Finding the chemical that would do the job was a classic case of trial-and-error without regard for the consequences of using poisons in the environment. Chemicals were solicited from all over the country and the world for study as candidates. The tests, done in uncontrolled environments with no safety precautions for low-level workers, consisted of dumping hundreds of different chemicals into three jars, one containing a lamprey, another native lake trout, and a third native blue gill. After hundreds of trials, a chemical that killed only the lampreys was selected for the job of eradicating the lamprey population. No thought was given to the possible effect on all the other native fish in the lakes—such as whitefish and sturgeon—or humans, or plants. (3) The same chemical is still used today to control the lamprey population, which remains but is no longer considered a problem.
There are many invasions into the Great Lakes. The lampreys were followed by alewives, a species of small fish. The population of alewives boomed at first, then busted, resulting in massive rafts of millions of dead alewives. Finally, the population of alewives stabilized and now are considered the primary prey of salmon that were introduced in the 1960s to serve the sport fishermen who are the backbone of Michigan’s tourist industry.
Zebra and quagga mussels proved to be one of most damaging of the invaders in the Great Lakes, partly because of how widely they spread. They were brought to the lakes in the ballast water of ocean-going ships. The open back door of the Great Lakes into the vast Mississippi River basin enabled the inevitable spread of quagga mussels throughout the country, eventually crossing the Continental Divide into western states. Those who tried to prevent that spread, spent many years imposing strict regulations about decontaminating and moving boats into places where mussels weren’t yet found. Today, places like Lake Powell have given up enforcing the regulations.
The mussels are filter feeders of phytoplankton that is food for creatures at the bottom of the food chain, depriving them of food, as well as their predators higher in the food chain. The mussels have turned sandy beaches into foot-slicing no-go zones. They improve the water clarity of the lakes, but that’s a mixed blessing for other inhabitants of the lakes.
Quagga and zebra mussels are now part of the food web. Populations of diving ducks have increased where mussels are found. A species of non-native fish—the goby—thrives on quaggas. And native whitefish, yellow perch, and chub have slowly developed the ability to digest quaggas, a story not fit for the squeamish. Whitefish don’t have the jaws needed to crack the mussel open, so they swallow them whole and leave it to their digestive system to deal with it: “the typical whitefish has an anus about the size of a ‘swizzle stick.’ But the fish excrement, a paste of crushed mussel shell thick as unset concrete, stretched the whitefish’s underside orifice to the diameter of his pinky.” (1)
The latest arrival is Asian carp via the Chicago River and sanitary canal from the Mississippi River into Lake Michigan. Asian carp were introduced to the Mississippi River to eat sewage pollution drained into the river by many rural communities. The prediction is that Asian carp will decimate the commercial fishery of the Great Lakes, though it is still early in that story.
More man-made problems
Not all problems in the Great Lakes are caused by the arrival of foreign aquatic species, but other problems are also man-made. Lake Erie is the most polluted of the Great Lakes. In summer months, when temperatures are high, there are toxic algal blooms that kill fish and pollute drinking water. Although the sources of pollution are man-made, the shallow lake bottom contributes to the problem. Lake Erie is the shallowest of the Great Lakes.
The Great Black Swamp at the western edge of Lake Eric slowly drained the watershed into Lake Erie, filtering and cleansing the water as it flowed through the swamp. The swamp was drained and filled to create more land for agriculture and remove an obstacle to westward travel and migration. Now the rich agricultural land that surrounds Lake Erie drains run-off of chemical fertilizers into the lake, providing the nutrients that produce algal blooms.
Climate change has already created chaos in the Great Lakes and the damage is expected to accelerate in the future. While the climate has warmed on land, the temperature of the water in the Great Lakes has climbed even higher, promoting growth of toxic algae. Winter temperatures are no longer low enough to freeze the lakes during the winter because the dark water of the lakes in the winter absorbs more heat than reflective white snow and ice. The higher temperature of the water in the lakes also increases evaporation of the water, lowering water levels, causing erosion of the exposed shore, and destroying infrastructure on the shore.
Moral of the Story
Problems in the Great Lakes were caused by humans who were accommodating their own needs. The aquatic animals blamed for the problems were only symptoms of the changes made by humans. They were not the cause. Eradicating them will not prevent new invasions in the future, so long as the gateways to other bodies of water remain open. And over time, many of the species that cause problems at first will enter the food web and become contributing members of the ecosystem. We fear change, but in many cases that is because our time frame for evaluating change is too short.
We should assume that similar problems have occurred wherever isolated bodies of water have been connected to serve human activities. The Suez Canal connected the Mediterranean Sea to the Red Sea in 1869. The Panama Canal connected the Atlantic Ocean to the Pacific Ocean in 1914. I can only imagine the consequences of removing the impassable barriers between those vast bodies of water.
To be clear, I don’t regret the building of most of the canal passages, with the possible exception of the St. Lawrence Seaway. However, it is not realistic to expect that the environment will not be altered by removing impassable barriers on water or land and it is pointless to blame the plant and animal species that are merely responding to the changes we have made.
(1) Dan Egan, Death and Life of the Great Lakes, W.W. Norton & Co., 2017
(2) Jerry Dennis, The Living Great Lakes, St. Martin’s Press, 2003
(3) The pesticide 3-trifluoromethyl-4-nitrophenol (TFM) is used to control sea lamprey (Petromyzon marinus) populations in the Great Lakes through its application to nursery streams containing larval sea lampreys. TFM uncouples oxidative phosphorylation, impairing mitochondrial ATP production in sea lampreys and rainbow trout (Oncorhynchus mykiss). However, little else is known about its sub-lethal effects on non-target aquatic species. The present study tested the hypotheses that TFM exposure in hard water leads to (i) marked depletion of energy stores in metabolically active tissues (brain, muscle, kidney, liver) and (ii) disruption of active ion transport across the gill, adversely affecting electrolyte homeostasis in trout. Exposure of trout to 11.0 mg l− 1 TFM (12-h LC50) led to increases in muscle TFM and TFM-glucuronide concentrations, peaking at 9 h and 12 h, respectively. Muscle and brain glycogen was reduced by 50%, while kidney and muscle lactate increased with TFM exposure. Kidney ATP and phosphocreatine decreased by 50% and 70%, respectively. TFM exposure caused no changes in whole body ion (N a+, Cl−, Ca2 +, K+) concentrations, gill Na+/K+ ATPase activity, or unidirectional Na+ movements across the gills. We conclude that TFM causes a mismatch between ATP supply and demand in trout, leading to increased reliance on glycolysis, but it does not have physiologically relevant effects on ion balance in hard water.” (Oana Birceanu, et.al., “The effects of the lampricide 3-trifluoromethyl-4-nitrophenol (TFM) on fuel stores and ion balance in a non-target fish, the rainbow trout,” Comparative Biochemistry and Physiology, March 2014)
Conservation Sense and Nonsense 
Excellent deconstruction of human intervention facilitating ‘invasion by invitation’.
Excellent article. You may want to read The Pathfinder By JF Cooper to get a picture of how the great Lakes was before white mans intervention. It’s one of his best. One can only dream of how this country was before we mucked it up (or if one is old enough there are those memories.)
Thanks for the suggestion.
I was surprised that, away from your familiar backyard issues, you slipped so easily into the vernacular of invasion biology, and especially into “monstering” mode.
That natural barriers exist is not evidence that they are supposed to. That their removal has unintended consequences tells us mainly that we’re poorly informed and have limited imaginations. Human agency was involved this time. That doesn’t mean the outcomes are automatically atypical. “Barriers” come and go. When they go suddenly, further catastrophic change is normal. Normal doesn’t mean pleasant or desirable. When we say “99% of all species on Earth have gone extinct” (since the beginning of life) we’re not describing a pre-technological golden age of peaceable belongingness.
That lamprey mouths give you nightmares and that their mode of predation is unsettling says nothing useful about lampreys. Jawless fishes aren’t aberrations. Evolution doesn’t make mistakes. There is no standard for mistakenness. Whatever results in another generation is what matters. And whether another generation occurs is merely a fact, not an imperative or a purpose. We’d have trouble demonstrating that anything other than humans reproduces for the sake of reproducing, or comprehends the connection between urgent behaviors and the appearance of offspring— which, by the way, are merely new individual competitors with their conspecifics, not taxonomic team members striving for some kind of group success through domination.
Despite the standard rhetoric, none of the species you mentioned invaded anything, literally or figuratively. Nor are they (therefore) characteristically, intrinsically invasive. Individual organisms simply did what they’ve always done, what they *can* do, under the prevailing circumstances. They know nothing of geography, energy flow, material cycling, food webs, ecosystems, biomes, or any of the other normative, systemic explanations we impose on them to suit our own sense of purpose and meaning. Furthermore, they have no political constituency, so our tax dollars are deployed in a mostly nonpartisan effort to scapegoat them as criminals. See (e.g.) https://www.iiseagrant.org/NabInvader/Lakes/suspects/suspects.html
Finally, there are extensive literatures about the Suez and Panama canals and resulting biotic redistributions (mostly relying on the popular “invasion” trope). For the Suez Canal, start here: https://en.wikipedia.org/wiki/Lessepsian_migration. The Panama Canal is less conveniently summarized, but in some ways it’s a harder situation to study. Some of the “invaders” there might surprise you. See https://wildlife.org/manatees-have-crossed-over-to-the-pacific/
Thank you very much for taking the time to write this informative comment. I agree with everything you say. I hope your comment will be read by everyone who reads the article.