At 2:30 p.m. on Friday, March 4, Erik Hanson got an urgent call from the state of Idaho: A sailboat was on its way to Montana, destined to hit Dayton Harbor, on Flathead Lake, at 10 a.m. Saturday—and it might have dangerous cargo.
Hanson took off from Missoula the next morning. Within minutes of the sailboat's arrival at Dayton, he spotted the cargo. It was clinging to the worn, blue keel of the 33-foot sailboat: a pea-sized quagga mussel.
Quagga mussels are an invasive species in North America.
Hanson is an invasive species expert for the intergovernmental Flathead Basin Commission. John Wachsmuth, Montana Fish, Wildlife and Parks regional coordinator for invasive species, joined him that morning. After Idaho's state invasive species coordinator, Amy Ferriter, tipped Hanson that the sailboat might not have been adequately decontaminated when it left quagga-infested Lake Mead, Nevada, Hanson called Wachsmuth, who coordinated the inspection of the boat. Although they'd learned the night before that the sailboat's owner was not going to put the boat in the water immediately, the need to be sure impelled Hanson and Wachsmuth to Dayton. The discovery of just one living quagga mussel was enough to stop inspecting and start the process of decontaminating the entire boat.
"If we get these mussels here, there is nothing that we can do," says Hanson. "They're going to spread everywhere, and there's going to be no way to contain them."
In the eastern United States and the Midwest, zebra mussels have disrupted aquatic ecosystems and caused billions of dollars of damage to water and hydropower systems. The zebra mussel's close cousin, the quagga mussel–"a zebra mussel on steroids," Hanson calls it–has also invaded the East. Then the quagga appeared in the West for the first time at Lake Mead in 2007. Since then, quagga mussel infestations have taken hold in dozens of other lakes and rivers in the West, fouling dams, water lines, boats, and anything else that remains in the water too long.
Montana is extremely vulnerable to zebra and quagga mussels as well as other aquatic invaders. The state has an enormous amount of fresh water that's popular with in-state and out-of-state recreationists who could bring such invaders into the state or move them around. With an extensive irrigation and hydropower infrastructure as well as a tourism industry that's solidly hitched to immaculate bodies of water and fishing, Montana ought to be afraid.
Frenzied carp hordes
In the spring of 2006, the white-bellied corpses of thousands of drum, a silvery-gray fish, floated just below the surface of Lake Erie. As waves pushed them to shore, the bodies piled up, forming walls of fish four feet high. The carcasses showed the signs of Viral Hemorrhagic Septicemia, or VHS: Bulging eyes, as if their heads had been cranked down in a vice, and skin that looked like it had been tattooed with red ink. The virus killed millions of fish in other places that year and has since spread to more lakes and rivers, killing still more fish.
Excessively lively fish, on the other hand, plague the Illinois River. There, and in many other drainages of the Mississippi River, Asian carp have taken over. The fast-growing, ravenous fish vie for food with the river's existing aquatic life; scientists have documented declining body sizes in native fishes such as the gizzard shad and the commercially important bigmouth buffalo since Asian carp appeared in the Illinois River in 1995. But scientific measurement isn't necessary to detect this invasion. Engine noise disturbs the carp, which can reach a density of over 4,100 fish per mile, causing frenzied carp hordes to fill the air in a motorboat's wake. That phenomenon has given rise to videos in which shirtless dudes motor down the river smacking the creatures out of the air with bats. A quick search on Youtube for "Asian carp baseball" or "zombie fishing" turns up dozens of such movies from across the Midwest.
Texas, meanwhile, is struggling with mussels. The North Texas Municipal Water District's pump at Lake Texoma has sat idle for two years due to fears that recently arrived zebra mussels will get into the district's water supply. The inoperable pump has reduced the district's water supply by almost a quarter; this April, the 1.6 million-strong district had to start conserving water. The precaution stems from experience in the Great Lakes where zebra mussels rapidly colonized water intake facilities, encrusting screens and pipes with billions of bodies at densities up to 70,000 per square foot. In 1989 and 1990, the town of Monroe, Michigan experienced severe water shortages and several outages due to the mussels. Other water facilities on the Great Lakes have spent millions trying to deal with the invasion.
Combined with maps that seem to show invasive species creeping and slithering across the continent, stories like these make the prospect of invasive species seem like a horror movie, which is perhaps half-right.
Invasive species are not zombies, monsters, or mutants. They are "aliens" only in the sense that they come from somewhere else on the planet. In their home ranges, they're usually either valued by humans or are a normal part of the ecosystem. Where the quagga and zebra mussels originate, near the Black and Caspian Seas, for example, predators and parasites have coevolved with the mussels and keep them in check. Asian carp are valued–indeed, celebrated–in China, where they've been part of the region's food and culture for 1,000 years. There is a common biology to invasive species, however. They're usually extremely adaptable, and can produce lots of young and disperse them widely.
Most of the invasive species that plague North America come from the Eurasian landmass. For thousands of years, Old and New World organisms evolved independently of each other. Columbus's voyage initiated a reunion of these worlds that resulted in a massive swapping of organisms, intentionally and unintentionally, which historians call the Columbian Exchange. Since 1492, the human webs of transportation and commerce have only thickened, bringing tens of thousands of exotic organisms to North America. A small percentage has qualities that can make them invasive. But to be invasive, they need human help. VHS can float free in lake water, carp can swim up rivers, and mussel larvae can drift downstream, but none of these organisms can cross land on their own to get into a new drainage.
Mostly, human help is unintentional. But sometimes it's deliberate, even if the consequences are unforeseen.
Kokanee double whammy
In the 1960s and 1970s, Montana Fish, Wildlife and Parks planted the opossum shrimp, Mysis relicta, in the Flathead drainage, hoping to augment the popular kokanee fishery. At its height, in Flathead Lake, fishermen hauled 100,000 kokanee out each year. By the late 1980s, after the establishment and explosion of Mysis, they caught...none. Something had obviously gone wrong.
Fisheries managers had based this ecological experiment on the phenomenal growth of kokanee in British Columbia's Kootenay Lake after the introduction of Mysis shrimp there. But Kootenay Lake had a unique upwelling current that made the shrimp, which normally hide on the lake bottom during the day, available to the kokanee. At Flathead Lake, not only did the shrimp not provide a food source for kokanee, but they competed with kokanee for its main zooplankton prey. The tiny shrimp did provide a food source to one fish, however: the bottom-dwelling, fish-eating lake trout. "Kokanee really got a double whammy," says Bonnie Ellis, a biologist at the Flathead Lake Biological Station. "Not only did Mysis eat the kokanee's favorite food, but Mysis then provided a food source for its major predator."