Thanks to invasive species, the shallowest Great Lake is in big trouble—again
AN ERIE DECLINE
Thanks to invasive species, the shallowest Great Lake is in big trouble—again
LAKE ERIE is in dire trouble, again. And that’s bad news for the entire Great Lakes system. Declared dead in the 1970s, Erie was healthier by the late 1980s than it had been in decades, thanks to a landmark international clean-up effort. But since the mid-’90s, scientists have documented a seasonal reappearance of an enormous, oxygen-deprived dead zone—evidence of a fundamental imbalance of the ecosystem—while massive mats of smelly algae float along shorelines. Last fall brought another disaster, with the corpses of thousands of loons, mergansers, other ducks and gulls washing up on Lake Erie’s shores. All the while, key fish populations are falling in Erie, the world’s most valuable freshwater fishery.
This time chemical pollutants aren’t the culprit. It’s a much more challenging problem of “biological pollutants.” Since the St. Lawrence Seaway opened in 1959,50 foreign
species have established themselves in Great Lakes waters, 36 of them—including the infamous zebra mussel and a tiny fish called the round goby—having arrived in the ballast water of transoceanic ships. These invasive species are dramatically altering the ecology in the world’s largest supply of surface fresh water and putting enormous stress on the lakes, says Gail Krantzberg, a biologist and Director of the International Joint Commission’s Great Lakes Regional Office. “The impacts are in the billions of dollars annually,” she says, from clogged water intake pipes to declines in fish populations and disruptions in natural ecosystems. Coping with zebra mussels alone costs an estimated $500 million per year.
The five lakes in question truly are great.
They hold 20 per cent of the world’s fresh water—enough to cover all of Canada to a depth of 2.7 m. Children of the last ice age 12,000 years ago, they’re part of an enormous drainage basin 520,000 sq. km in size, home to 34 million people, 6.4 million of them in Canada. Until relatively recently, they were safe from aquatic invaders. Few species could negotiate the series of rapids on the St. Lawrence River, including Montreal’s Lachine and the Long Sault near Cornwall, Ont. Niagara Falls isolated Lake Ontario from the upper lakes. Erie, Huron and Michigan were essentially one body of water separated from the biggest of them all, Superior, by another series of rapids on the St. Mary’s River.
But the rapids impeded not only marine life but surface traffic as well. As long ago as 1680, an energetic Montreal seminarian, François Dollier de Casson, launched a project to build a 1.5-m-deep canal to bypass the Lachine Rapids. A formidable task, it was not to be completed until 1824. Four years later, the Erie Canal connected Lakes Ontario and Erie to the Atlantic. Many more canals followed, including the Welland that bypasses Niagara Falls to link Ontario to Erie, and others on both sides of the St. Mary’s.
A primitive, unattractive fish from the Atlantic was probably the first species to invade the newly accessible lakes. The sea lamprey reached Lake Ontario in the 1830s, later gaining access to Lake Erie and the upper lakes. By the late 1940s, this vampire of the seas had decimated lake trout and other critical fish species. Canadians weren’t worried about invaders from the sea when they cheered the opening of the Seaway in 1959. But in welcoming the world’s ocean-going traffic, the Seaway also opened the way to foreign invaders, forever changing the ecology of the Great Lakes basin.
The fingernail-sized zebra mussel, native to the Caspian Sea region, was the wake-up call. At first, in 1988, it seemed just an expensive nuisance—clogging water intake pipes and forcing swimmers to wear shoes as protection against the carpet of knifeedged shells. But then native mussel species
started disappearing—13 in little Lake St. Clair (between Huron and Erie), 10 more in western Lake Erie. As the shallowest and warmest of the Great Lakes, Erie is usually the first to show signs of stress. Zebras blanketing large areas of lake bottoms with up to 400,000 per square metre have changed the ecology of the lakes. As filter feeders, zebras suck in water and ingest its phytoplankton-microscopic plants that are the basic food resource for small fish and invertebrates such as diporeia, an important shrimp-like species.
Paradoxically, Lake Erie is now clearer than it’s been in living memory, thanks to the enormous amount of phytoplankton being removed by the zebras. But diporeia, which normally account for up to 70 per cent of the living biomass of any lake bottom, have disappeared from large areas. And as the ecological dominoes fall, the absence of diporeia, a vital food source for smaller fish like alewife, bloater, smelt and sculpin, means less food for the bigger and commercially important fish—trout, perch,
walleye and salmon. Not surprisingly, perch and walleye populations are declining.
Meanwhile, as the zebras vacuum up all that phytoplankton, they eject enormous volumes of waste that is high in algae-promoting phosphorus. One result: recent algal blooms causing taste and odour problems for municipal water supplies. Another may be dead zones. Scientists speculate that the combination of zebra mussel waste and clearer water allows algae to grow at greater depths, where there is less oxygen. When they decay, what little oxygen is there is used up, creating a dead zone.
Then there were those corpses of thousands of loons and other water birds. “No one could have predicted that zebra mussels would end up killing waterfowl,” says Hugh Maclsaac, aquatic ecologist at the University of Windsor and an expert on invasive species in the Great Lakes. As the zebras filter massive amounts of water, they also ingest and absorb toxins and contaminants. Diving ducks such as the greater and lesser scaup thrive on zebras, and their population boomed—for awhile. For the past few years, scaup have been dying in large numbers as a result of type-E botulism, a toxin produced by a bacterium that concentrates inside the zebras.
Few Great Lakes bird or fish species eat zebras directly, but another Eurasian invader, the round goby, gobbles them up. That tiny fish was first spotted in the St. Clair River between Huron and Erie in 1990. It soon spread throughout the lakes, becoming the most common fish in parts of Lake Erie. But as gobies gorge on zebras, they further concentrate the contaminants and bacteria that the mussels have filtered from the water. Loons, mergansers, gulls and other fish-eating birds that feed extensively on the gobies become poisoned and die. The toll, growing steadily over the past four years, has become horrendous. “We found more than a thousand dead loons on the beaches of Lake Erie’s Long Point alone last October,” says Steve Timmermans, Aquatic Surveys Scientist at Bird Studies Canada.
As new species continue to enter the lakes we can expect more of these “weird, synergistic combinations” that have unpredictable impacts, says Anthony Ricciardi, an aquat-
ic ecologist at the Redpath Museum in Montreal. Of the thousands, both aquatic and land-based, that have arrived over the years, 170 have established themselves in and around the Great Lakes, Ricciardi says, with new invaders being discovered on average every eight months, and many more on their way. “They’re on the move in Europe,” he says, “and will arrive here sooner or later.” One already here is a tiny, centimetrelong invertebrate called the fishhook water flea, another ballast-water invader that Maclsaac first encountered in Lake Ontario in 1998. Within a year it spread through Erie and Huron to distant Lake Michigan. The fishhook water flea eats zooplankton, the basic food for most larval fish, making it yet another threat to the Great Lakes’ multi-billion-dollar sports and commercial fishing industry. “The ecology of the lakes is unmanageable now,” says Maclsaac. “We don’t know what’s going on.”
On a more positive note, no new fish or mussels have spread from ballast water since 1993. U.S. regulations requiring all ships to
exchange their ballast water in the ocean or seal their tanks before entering the Seaway can take much of the credit. “Canadian regulations are still voluntary,” says Dave Reid, a scientist at the Great Lakes Environmental Research Lab in Ann Arbor, Mich., “with no inspections.” Early this year, the U.S. Congress passed legislation that adds more clout to American control efforts. All states on the lakes must develop plans for dealing with foreign species, and all ships put into service after 2005 must have on-board treatment systems for ballast water. It would also make US$180 million available each year to fight the pests and address the need for public education, early detection and rapid response measures.
And Canada? Not only is there no comparable legislation in the works, the federal government is doing nothing about aquatic invasives, says Johanne Gélinas, commissioner of the environment and sustainable development. “Instead,” she says, “the Canadian government has an open-door policy.” Ottawa committed itself to developing a strategy for invasives after the 1992 Rio Earth Summit, but the problem just gets worse, not only in the Great Lakes but throughout Canada’s land and waters. “These things pose a hazard to the Canadian economy on the order of billions of dollars in damage and control costs,” says Windsor’s Maclsaac. “We’re paying a high price for doing nothing,” agrees Ricciardi.
Keeping every potential invader out may be impossible. But reducing the numbers and barring the worst ones to minimize the impact would be a smart strategy. Despite two scathing reports by Gélinas, commitments from three ministries and interest from individual MPs, there has been little progress, says the commissioner.
If riding this slow-motion ecological train wreck isn’t reason enough to take action, the economic consequences of exporting these invaders to other countries ought to be. In 2001, a U.S. ban on imports of P.E.I. potatoes over a suspected fungal disease cost at least $22 million in lost sales. And no one in Ottawa should forget the one-week Toronto travel warning over SARS—a virus carried from Asia—that stole a billion dollars from the economy. Other new invaders aren’t going to wait for us to get our act together, says Ricciardi. And once they’ve carved out a niche here, the environment is changed forever. ffl
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