The spread of zebra mussels and quagga to the west shows how small invaders can cause big problems

The zebra mussel has been a petty invasive species since it wreaked economic and ecological havoc on the Great Lakes in the late 1980s. However, despite intense efforts to control it and its relative, the mussel, these fingernail-sized mollusks spread across American rivers, lakes, and bays, clogging water supply pipes and altering food webs.

Now, the mussels threaten to reach the last uninfected freshwater areas of the country to the west and north: the Columbia River Basin in Washington and Oregon, and the waterways of Alaska.

As an environmental historian, I study how people’s attitudes toward non-native species have changed over time. Like many other aquatic aliens, zebra mussels and kuga spread to new bodies of water when people move them, either accidentally or on purpose. Human-built structures, such as canals, and debris can also help invaders bypass natural barriers.

In my view, limiting the damage from these outbreaks – and if possible preventing them – requires understanding that human activities are the root cause of costly biological invasions.

The zebra and kuga mussels moved east, south, and west from the Great Lakes to many other American rivers and lakes.

Past ocean invasions

European exploration of the Americas between the late 14th and 18th centuries led to massive transfers of organisms, a process known as the Columbian exchange, named after Christopher Columbus. Many investors became wealthy by shipping livestock and agricultural crops across oceans. Transatlantic travel also introduced microbes that caused infectious diseases, such as smallpox and measles, that killed millions of immunocompromised Native Americans.

During the 19th century, European and North American colonists established acclimation societies to import desirable species of foreign animals and plants to use for food, sport hunting, or beautify their environments. Many of these efforts failed when the introduced species could not adapt to their new conditions and died.

Others have caused legendary environmental disasters. For example, after the Victorian Adaptation Society released European rabbits in Australia in 1859, they multiplied rapidly. Feral rabbits and other introduced species such as cats have destroyed millions of Australia’s native plants and animals.

Maritime transport also led to the accidental spread of alien species. Man-built canals made it easier to transport goods, but also provided new paths for aquatic pests.

During the late 19th and early 20th centuries, for example, Canada expanded the Welland Canal between Lake Ontario and Lake Erie to allow large ships to bypass Niagara Falls. By 1921, these technological improvements enabled marine lamprey, a parasitic fish, to move from Lake Ontario to the upper Great Lakes, where they remain a serious threat to commercial fisheries.

In 1959, the United States and Canada opened the St. Lawrence Seaway, a marine network linking the Atlantic Ocean with the Great Lakes. Oceanic ships using the sea lane brought surreptitious species in ballast water – tanks filled with water, used to keep ships stable at sea.

Water pours from a port on the bow of a large carrier ship into the port.
A ship moored in Southampton, England, discharging ballast water.
Peter Titmuss / UCG / Universal Images Group via Getty Images

When the ships reached their destination and dislodged their ballast tanks, they released exotic plants, crustaceans, worms, bacteria, and other organisms into the local waters. In a 1985 study, Williams College biologist Jim Carleton described how ballast water discharges provided a powerful avenue for biological invasions.

Invasion of mussels in the Great Lakes

Zebra mussels are native to the Black and Caspian Seas. They are believed to have entered North America in the early 1980s and were officially recognized in the Great Lakes in 1988, followed by mussels in 1989.

Soon, striped bivalves were covering hard surfaces all over lakes and washing up on beaches, cutting off beachgoers’ feet. Zebra mussels clog intake pipes in drinking water treatment plants, power plants, fire hydrants, and nuclear reactors, dangerously reducing water pressure and requiring expensive treatments.

Slugs are filter feeders that make the water more pure. But the zebra and kuga mussels leached so much plankton from the water that they starved the local mussels and promoted harmful algal blooms. The invaders also passed on the deadly type E food poisoning to the fish-eating birds.

By the early 1990s, 139 alien species had been established in the Great Lakes region, nearly a third of which arrived after the opening of the St. Lawrence Seaway. Ship-related introductions, along with other pathways, such as aquaculture, aquariums and bait fish release, have transformed the Great Lakes into one of the world’s most invasive freshwater ecosystems.

Local officials are grappling with the infestation of zebra mussels in Brownwood Lake, Central Texas.

Early political responses

The United States began regulating ballast water management in 1990 but had trouble filling the gaps. For example, ships declaring that they had no pumpable ballast water on board did not have to empty and refill their ballast tanks in the middle of a voyage with clean ocean water. As a result, live freshwater organisms lurking in reservoir sediments can still be released into vulnerable harbors.

Finally, after extensive studies, in 2006 the United States and Canada required ships to wash tanks containing residual sediments with seawater. A 2019 assessment found that only three new species were established in the Great Lakes region from 2006 to 2018, none of which were used via ship ballast.

Now, however, other human activities are increasingly contributing to the harmful introduction of freshwater – and with shipping regulated, the main culprits are thousands of private boats and fishermen.

Stop spreading to the west

Zebra and kuga mussels move west and south from the Great Lakes, attached to special boats or carried in bilge waters and bait buckets. They are found in Nevada, Arizona, California, Utah, Colorado, and Montana.

If mussels reach the Columbia River ecosystem, they will threaten local wildlife, irrigation pipes, and dams vital to agriculture and hydropower. Government officials, wildlife managers, and scientists are working hard to prevent this from happening.

Communication with the audience is crucial. Passengers who move their boats without clearing them of pollution can take zebra mussels and kuga to inland rivers and lakes. Mussels can live out of the water in hot places for weeks, so it’s important for boaters and fishermen to clean, dry, and dry their boat gear and fishing gear.

Aquarium keepers can help stop tides by disinfecting tanks and accessories in order to prevent the accidental release of organisms into public waterways, and by being vigilant about their purchases. In 2021, zebra mussels were discovered in imported algae balls sold as aquarium plants throughout the United States and Canada.

The USGS maintains a website where people can report sightings of non-native aquatic species, which may detect new outbreaks during the critical early stage before they can be established.

Maintain public support

Some of these efforts have shown encouraging results. Since 2008, Colorado has operated a rigorous boat inspection program that has kept zebra mussels and kuga out of state waters.

But prevention is not always common. Officials closed the San Giusto Reservoir in central California to the public in 2008 after zebra mussels were found there; Residents argue that the shutdown has harmed the community and are pressing the federal government to eliminate the mussels in order to reopen them for fishing.

Mitigating the devastating effects of invasive species is a complex task that may not have a clear end point. It takes scientific, technological and historical knowledge, political will and skill to convince the public that everyone is part of the solution.

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