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Wednesday, August 17, 2022

Westward dispersal of zebra and quagga mussels shows how small invaders can cause big problems

The zebra mussel has been a poster child for invasive species since the economic and ecological devastation struck the Great Lakes in the late 1980s. Yet despite intense efforts to control it and its relative, the quagga mussel, these fingernail-sized mollusks continue to spread through American rivers, lakes and creeks, clogging water supply pipes and altering food webs. are.

Now, the mussels threaten to reach the country’s last major uncultivated freshwater areas 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-indigenous species have changed over time. Like many other aquatic aliens, zebra and quagga mussels spread to new bodies of water when people accidentally or intentionally take them in. Man-made structures, such as canals, and debris can also help invaders overcome natural obstacles.

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

Zebra and quagga mussels have migrated east, south, and west from the Great Lakes into many other American rivers and lakes.

past transoceanic invasion

European exploration of the Americas between the late 1400s and the 1700s led to the mass transfer of organisms, a process known as the Columbian Exchange, named after Christopher Columbus. Many investors prospered through the shipping of livestock and plantation crops across the oceans. Transatlantic travel also introduced the germs that caused infectious diseases such as smallpox and measles, which killed millions of Native Americans who lacked immunity.

During the 19th century, European and North American colonists established adaptation societies to import desired species of exotic animals and plants for food, game hunting or to beautify their environments. Many such attempts failed when introduced species could not adapt to their new conditions and died out.

Others triggered mythical ecological disasters. For example, after the Victorian Acclimatization Society released European rabbits to Australia in 1859, they multiplied rapidly. Other species such as wild rabbits and cats have destroyed millions of native plants and animals in Australia.

Shipping has also accidentally spread alien species. Man-made canals facilitated freight transport, but also provided new avenues for aquatic insects.

For example, in the late 19th and early 20th centuries, Canada expanded the Wayland Canal between Lake Ontario and Lake Erie to allow larger ships to bypass Niagara Falls. By 1921, these technological improvements enabled the transfer of the sea lamprey, a parasitic fish, from Lake Ontario to the upper Great Lakes, where it still poses a serious threat to commercial fisheries.

In 1959, the US and Canada opened the St. Lawrence Seaway, a maritime network that connects the Atlantic to the Great Lakes. Sea-going ships brought in ballast water with stowaway species – tanks filled with water, used to keep ships stable at sea.

Water Is Fed From An Outlet At The Bow Of A Large Bulk Carrier In Port.
A ship parked in Southampton, England pours ballast water.
Peter Titmus / UCG / Universal Image Group via Getty Images

When the ships arrived at their destination and drained their ballast tanks, they released exotic plants, crustaceans, insects, bacteria and other organisms into the local waters. In a landmark 1985 study, Williams College biologist Jim Carlton described how ballast water discharges provided a powerful vehicle for biological invasions.

Great Lakes Mussel Invasion

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

Soon striped bivalves were blanketing hard surfaces throughout the lake and washing up on the shoreline, cutting off beach legs. Zebra mussels clog intake pipes in drinking water treatment plants, power stations, fire hydrants and nuclear reactors, dangerously depleting water pressure and requiring expensive treatment.

Mollusks are filter feeders that usually clean water. But zebra and quagga mussels filter so much plankton out of the water that they starve native mussels and promote harmful algal blooms. The invaders also passed the deadly type E botulism to the fish-eating birds.

By the early 1990s, 139 exotic species had become established in the Great Lakes, with about a third arriving after the opening of the St. Lawrence Seaway. Ship-related introductions to aquaculture and other routes such as aquarium and forage fish release transformed the Great Lakes into one of the world’s most invaded freshwater ecosystems.

Local officials battle a spreading infection of zebra mussels at Brownwood Lake in central Texas.

initial policy responses

The US began regulating ballast water management in 1990, but has had trouble plugging the loopholes. For example, ships declared that they do not have pumpable ballast water on board are not required to empty and refill their ballast tanks in the middle of the voyage with clean sea water. As a result, freshwater organisms still lurking in tank sediments can be released into vulnerable ports.

Finally, after extensive study, in 2006 the US and Canada required ships to flush tanks containing residual sediment with seawater. A 2019 assessment found that only three new species were established in the Great Lakes from 2006-2018, none of them through ship ballast.

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

westward spread

Zebra and quagga mussels are moving west and south from the Great Lakes, attached to private boats or carrying water and bait in buckets. They have been found in Nevada, Arizona, California, Utah, Colorado and Montana.

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

Public relations is important. Travelers who transport their boats without disinfecting them can transfer zebra and quagga mussels to rivers and lakes inland. Mussels can live out of water for weeks in hot places, so it is important for boaters and anglers to clean, dry and dry boating equipment and fishing gear.

Aquarium keepers can help stem the tide by disinfecting tanks and accessories to prevent the accidental release of live organisms into public waterways and by being vigilant about their purchases. In 2021, zebra mussels were detected in imported moss balls sold as aquarium plants in the US and Canada.

The US Geological Survey maintains a website where people can report sightings of non-indigenous aquatic species, potentially spotting new infections during the critical early stage before they become established.

maintain public support

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

But prevention isn’t always popular. Officials closed the San Justo Reservoir in central California to the public in 2008 after zebra mussels were found there; Residents argue the closure has harmed the community and are lobbying the federal government to eradicate the mussels to reopen it for fishing.

Mitigating the devastating effects of invasive species is a complex mission that may not have a clear endpoint. It requires scientific, technical and historical knowledge, political will and skill to convince the public that everyone is part of the solution.

World Nation News Desk
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