Sea of change
Led by zebra mussels, a host of invasive species is wreaking
ecological havoc in Lake Michigan
By Dan Egan
Milwaukee Journal Sentinel
Published December 19th, 2004
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
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.
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
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
"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
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
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 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
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
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
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
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
"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
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."