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|Invasive species, wreaking ecological havoc in Lake Michigan|
|Written by Milwaukee Journal Sentinel|
|Saturday, 18 December 2004 10:34|
The Great Lakes zebra mussel invasion in the late 1980s didn't initially create alarm.
It didn't even raise eyebrows.
A student on a field trip plucked the first cluster of fingernail-size mussels from the waters of Lake St. Clair in the summer of 1988. She didn't know what she had. Neither did her professors at Ontario's University of Windsor, who sent a sample to a mollusk expert in Europe.
The diagnosis came back: Dreissena polymorpha, a tiny but prolific filter feeder native to the Caspian Sea region that spreads as tiny larvae on lake currents.
Nobody panicked. The Dutch, after all, had even planted them to clean some of their dirtiest waters.
But University of Windsor professor Hugh MacIsaac remembers the day back in 1991 when he was punching numbers into a computer trying to predict the environmental impact of the diminutive fugitives, which scientists believe invaded the world's largest freshwater system as stowaways in the belly of a freighter.
MacIsaac was analyzing how much water a single zebra mussel could filter in a day, and how many of the rapidly reproducing mollusks could be found on the bottom of Lake Erie.
The numbers stunned him.
"I was just looking at the data, and I couldn't believe it," he says. "It was telling me that these mussels were conceivably filtering western Lake Erie seven times per day - filtering all of the water to strip the food seven times in one day."
Further studies showed that waters near the bottom of the lake likely take the brunt of the vacuuming.
Nevertheless, MacIssac was "blown away."
"It was unprecedented," he said. "There was nothing that was capable of filtering like that."
The Great Lakes would never be the same.
Invasive stowaways Mussels linked to food
problems, fouled beaches
Most of the public welcomed the subsequent increase in water clarity, mistakenly believing that clearer means cleaner - and not a profound shredding of the base of a food web that had been delicately knit over thousands of years, isolated from the rest of the aquatic world by the biological barrier known as Niagara Falls.
The first hint of a downside to the untold billions of zebra mussels spilling across an ecosystem where they have no native predator came in the early 1990s. Clusters of mussels started to plug pipes at power plants and city drinking systems. The economic costs alone are now more than $3 billion per decade, according to 2002 estimates by the General Accounting Office.
The ecological cost might prove incalculable. Invasive mussels are now being linked to everything from a collapse of the bottom of the Great Lakes food chain to the noxious weedy sludge along Wisconsin's Lake Michigan shoreline to an explosion in toxic algae blooms across the region.
Lake Michigan has weathered environmental calamities. Thanks largely to the Clean Water Act of 1972, it rebounded in the last generation from decades of industrial dumping and, Milwaukee's periodic sewer overflows notwithstanding, its shores are far from the cesspool they were before the arrival of modern sewage treatment.
There are other ecological successes. Scientists used poison to control, but not eliminate, the invasion of lake-trout-killing sea lamprey in the mid-1900s. And shortly thereafter biologists managed an invasion of beach-fouling alewives by planting hundreds of millions of Pacific salmon to eat them.
But that tinkering has perhaps given the public a false confidence in humans' ability to fix the Great Lakes when something goes wrong. Beneath the lakes' shimmering surface, a mounting number of invasive species are wreaking an ecological havoc that scientists are having a hard time understanding, let alone stopping.
Today, at least 180 non-native species lurk in the lakes, and a new one arrives, on average, every eight months. Most come in the ballast water of commercial ships that shuttle between the Great Lakes and Atlantic Ocean via the St. Lawrence Seaway, a largely artificial link between the two aquatic worlds that opened for business in 1959.
Some invasive stowaways are no bigger than an eyelash; they never earn more than their scientific name, and slip without even a ripple into the food web.
Others, either alone or acting in concert with fellow invasive species in ways that science cannot predict, bring devastation that extends beyond the water.
In Lake Erie, for example, a food chain reaction that started on the lake bottom has led to botulism outbreaks in recent years that have killed tens of thousands of birds.
It is a lesson in biological pollution that is as simple as it is frightening:
Invasive mussels have increased Erie's water clarity.
That has led to a bloom in algae growth on the lake bottom.
That material eventually dies, and its decomposition burns massive amounts of oxygen.
That opens the door to botulism-causing bacteria that thrive in oxygen-depleted environments.
The mussels suck up that bacteria and are, in turn, eaten by round gobies, a fish invader from Europe that followed the mussels into the region via ocean freighters.
The poisoned gobies become paralyzed and are easy prey for birds like loons, grebes and gulls.
The birds die.
"It's incredible. We couldn't have seen this coming," says Anthony Ricciardi, an invasive species expert from Montreal's McGill University. "Invasions can produce ecological surprises, and most surprises are nasty. And this is one of them. And there will be more."
Fixing the lakes' previous pollution problems suddenly looks simple.
"In the '60s and '70s we were looking at chemistry - pollution from a chemistry standpoint - and we were able to solve that because we cut off the loads of chemicals," says Cornell University biologist Ed Mills.
Technology - and stiff federal legislation - fixed many of the problems related to raw sewage, dioxin, PCBs and mercury. Biological pollution is a different story.
It is, literally, a pollution with no smokestack to cap; Ricciardi says all of the species that have invaded the Great Lakes in the last 200 years are alive in the lakes today - and breeding.
"It's the pollution," says MacIsaac, "that is basically non-ending."
Fish food falloff Scientists finding
'vast underwater deserts'
Lake Michigan salmon angler Jack Johnson sees no downside to the zebra mussels. The Highwood, Ill., resident says the chinook fishing is as good as it's been in recent memory, and Lake Michigan's water looks better than ever.
He holds up one of his cannonball sinkers and explains that in the 1970s and '80s the shiny silver baseball-size fishing line weights used to disappear within five feet of the surface. Today he can see them shimmer at depths approaching 30 feet.
"It's cleared up the lake quite a bit," he says. "So far it's been beneficial on the fishing end of it."
But scientists see trouble ahead for all sorts of Lake Michigan's fish species because the zebras and their cousin, the quagga mussel, also an invader from the Caspian Sea region, are evidently taking their toll on a tiny creature that has for thousands of years been a primary foundation of the Lake Michigan food web.
The quarter-inch crustaceans, shrimp-like creatures called diporeia (die'-poor-EYE-ah), have historically blanketed the bottom of Lake Michigan and are a critical food source for the prized native whitefish. They also are a key component of the diets for forage species such as chubs, alewives and smelt, which in turn feed the salmon and trout that drive a Great Lakes recreational fishing industry that brings in an estimated $4.5 billion annually.
Scientists used to find as many as 20,000 diporeia per square meter. Now, in some areas of the lake, a diporeia die-off has essentially created "vast underwater deserts," says Andy Buchsbaum, director of the National Wildlife Service's Great Lakes office.
It is a situation Buchsbaum calls "ecosystem shock."
Nobody's figured out the precise link between the rise of the mussels and the demise of the diporeia, but few doubt there is a connection. One theory is the mussels are sucking away the microscopic plankton the diporeia depend upon.
The drop, which has also occurred elsewhere in the Great Lakes, is having more than theoretical consequences.
Cornell's Mills says Lake Ontario's whitefish population is literally running out of food.
"They're emaciated," he says. "They're definitely starving."
Whitefish going hungry Bottom drops out
on food chain
It is a similar story for whitefish in Lake Michigan, particularly in the waters off Door County, historically one of the region's most productive fishing grounds. The species made famous by the popular fish boils historically depended on fat-rich diporeia for up to 75% of its diet.
Now, with the diporeia disappearing, the whitefish are trying to consume zebra mussels. Washington Island-based commercial fisherman Ken Koyen has seen this firsthand, and it isn't a pleasant sight. Whitefish don't have teeth, and therefore can't crack the zebra's shell to suck out the flesh.
"The whitefish eats the whole works, then their stomach grinds it up and passes it," he says. The mussels shred the whitefish innards. "It looks like hemorrhoids; it actually pushes part of their intestine out."
Koyen saw this for the first time in a few whitefish in the summer of 2003. This year he's had days when he harvests populations of whitefish that are apparently eating nothing but zebra mussels.
"I wouldn't doubt the zebra mussels will kill them eventually," he says.
Whitefish aren't the only fish affected. Head out for one of Milwaukee's famous Friday night fish fries, and it's almost a sure bet you're not getting the same meal that hooked your parents or grandparents. Wisconsin's Lake Michigan perch population has crashed by about 90% in the last decade, and commercial harvests stopped on Lake Michigan in 1996, except for in the waters of Green Bay.
That means Milwaukee's Friday night perch orders are likely filled by stocks from far away places like Canada, or even substitute species shipped from Europe.
There is debate about precisely why the perch are struggling. Overfishing is one likely reason, but mussels also could be a culprit because the diporeia-feeding juvenile perch may not be finding enough to eat. Another theory is the increased water clarity has boosted perch's vulnerability to predators.
The drop in the diporeia could prove more devastating than the sea lamprey invasion of the 1950s, because the food chain is being attacked at its must vulnerable point - the bottom.
"When you tear away the bottom of the food chain, everything that is above it is going to be disrupted," says Tom Nalepa, a research biologist with the National Oceanic and Atmospheric Administration.
That could include humans.
Toxic algae blooming Zebra mussels blamed
for green film on water
Zebra mussels have also been linked in some areas of the Great Lakes basin to outbreaks of a toxic blue-green algae called microcystis, which produces a poison deadly to pets and livestock, and in some cases humans.
In the 1960s the shamrock-green film plagued Midwest waterways that were overloaded with nutrients from sewage spills and farm runoff. Pollution controls in the 1970s limited those outbreaks, but recent research from Michigan State University shows that zebra mussels are the likely culprit in what are becoming routine microcystis outbreaks in lakes Erie and Huron and inland lakes across the Upper Midwest. The mussels foster algae blooms because they tend to eat everything in the water but the microcystis; lab experiments show the mussels literally spitting out microcystis, which produce a toxin called microcystin.
"They (mussels) selectively reject these toxic algae, so over time they're favoring these colonies," says Gary Fahnenstiel, a senior ecologist with NOAA. "The more zebra mussels you have in a body of water, the more likely you're going to find microcystis being abundant."
In Michigan's Muskegon Lake, for example, tests taken this fall show microcystin levels were at times 10 times higher than the levels the World Health Organization considers safe for swimming - and more than 100 times beyond the WHO standards for drinking water. It appears that zebra mussels are actually undoing the pollution-control gains made a generation ago.
There are also concerns that the toxins could be accumulating in fish, and may even become airborne.
"I don't want to scare anybody, but it should be a cause for concern," says Fahnenstiel.
A broader invasion Other species pose
major threats to lake
The zebra mussel might be the poster child for Great Lakes invasive species, but it isn't the only invader that has tossed the aquatic world into chaos. The round goby, a cell-phone-sized aggressive forager, eats around the clock, squeezes native fish out of prime spawning habitat and preys upon eggs of native species.
The perch-like ruffe was introduced via ballast water to Lake Superior in the mid 1980s, and has spread to Lake Michigan. The fear is it could further squeeze out what is left of the lake's perch population.
Two crustaceans with spikes on their backs that make them largely inedible to forage fish have recently established themselves in the lakes' food-chain, and scientists are bracing for two European species of shrimp invaders to arrive via freighters due to lax ballast-water regulations. One is dubbed the "killer shrimp" because the voracious predator doesn't always bother to eat the prey it kills. The other builds tubes out of lake sediment, and is capable of quickly coating a lake bottom with a four-inch layer of mud.
"The zebra mussel is not the last high-impact species we're going to see," says McGill University's Ricciardi. "Not at all. There are plenty that are coming."
Perhaps most menacing is the Asian carp's steady migration north up the Mississippi and Illinois rivers. The fish, which escaped southern aqua-farms over a decade ago, is now within about 40 miles of Lake Michigan. The only thing standing between the fish and the lakes is a temporary electric barrier on the Chicago Sanitary and Ship Canal designed to repel but not kill it. If the fish get into the lakes, the ecological toll could be unprecedented; University of Wisconsin Sea Grant Institute's Phil Moy has likened Asian carp to "a 100-pound zebra mussel that swims around all the time."
Wisconsin Department of Natural Resources biologist Paul Peeters says every new species likely will have a negative impact on some existing species.
"Think of Lake Michigan like a pie tin," he says. "You can only have so much in that pie tin, and if something new comes in, something else is going to suffer. You don't get a bigger pie tin."
And you don't get to take any of those species out of the tin.
Alarm bells Pace of change seems
to be accelerating
UW Sea Grant's Jim Lubner says people are beginning to realize something is wrong with Lake Michigan.
The Great Lakes, he says, have been ever-changing since the widespread settlement of the region in the 19th century, and people have always learned to live with those changes. They figured out how to co-exist with the introduction of European carp, they've learned to cope with the demise of the lake trout and the outbreaks of dying alewives.
But what has been happening in the last 10 or 15 years is different.
"It used to be you'd say, 'My grandfather would say they never had this stuff before.' " says Lubner. "Now, it's 'I don't remember this a couple of years ago.' "
Sheldon Wasserman doesn't remember Lake Michigan stinking like a sewer a decade ago.
Some of of his fondest childhood memories are family trips to Milwaukee's Bradford Beach, building sand castles and splashing about the tumbling Lake Michigan surf.
Today the 43-year-old physician and state representative lives about a mile from that very place. He doesn't take his own children there. He has no desire to go to a beach where waves can roll in thick and black as oil, a place that too often "smells like something died."
The sewage-smelling gunk that has come to plague pockets of Wisconsin's Lake Michigan shoreline in late summer during the past five years is tied to an explosion of brilliantly green seaweed rooted on the lake bottom.
The algae, called cladophora, eventually die and wash ashore and decompose in a stew that stinks like sewage.
This is not a new problem. Lake Michigan's beaches were choked with the nutrient-loving stuff in the 1960s, but it diminished with the arrival of better sewage treatment and new pollution rules.
Zebra mussels are implicated in its return because they have, ironically, made the lake almost Caribbean-clear in places, and that has opened the door for new crops of the sunlight-dependent plant to grow on vast expanses of lake bottom.
"If you go diving and see how much is on the bottom of the lake, what you're seeing on the beach is just the tip of the iceberg," says UW-Milwaukee researcher Harvey Bootsma. "It's like a forest or a very thick lawn of green grass. For as far as you can see."
Wasserman first noticed the stench a few years ago.
He still hasn't come to terms with the idea of learning to live with it.
"It's unbearable, and you say to yourself: What is going on?" he says. "We have this beautiful natural wonder, one of the greatest freshwater lakes in the world, and . . . it basically looks like a disaster."
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