Great Lakes Exotic Species:
Zebra mussels spreading
Boaters, ducks probably introduced
invasive species into inland lakes, rivers
BY LU ANN FRANKLIN Times Correspondent
Industries along Lake Michigan that
use lake water for manufacturing have been plagued by
zebra mussels clogging intake valves since the small fingernail-size
freshwater mollusks were introduced accidentally into
the Great Lakes in 1988 by a transoceanic vessel.
This pesky species steadily has invaded
inland waterways in Northwest Indiana's three counties
and is now threatening the ecosystem of these lakes and
Wolf Lake in Hammond became the first
inland waterway outside Lake Michigan to be invaded by
the aquatic nuisance species. Adult zebra mussels were
discovered there in 1991. Since that time the invasion
has been progressive, reaching Pine and Stone lakes in
LaPorte County in 1997, Cedar Lake and Deep River in Lake
County in 1998 and Flint Lake in Porter County in 2000.
Throughout the state of Indiana, there are currently 50
lakes and rivers infested with zebra mussels, according
to the Indiana Department of Natural Resources Division
of Fish and Wildlife.
Recreational boaters have unwittingly
helped spread zebra mussels, said Brian Breidert, a biologist
with the DNR office in Northwest Indiana.
When a boat travels through Lake Michigan
waters or other areas with zebra mussels, the microscopic
free-swimming young zebra mussels make their way into
the boat's intakes and also attach themselves to the boat
trailer. If the owner then launches the craft into another
body of water without a thorough cleaning and drying out
period, the zebra mussels are released into that waterway.
"It's important for recreational boaters
when they pull out of the lake to chlorinate their boat
to help reduce the spread of this invasive species," Breidert
The bilge of the boat should be emptied,
and household bleach in a 10 percent solution should be
used to cleanse the hull of the boat and trailer as well
as water intakes.
Breidert said he doesn't recommend
using bleach in a live well on a boat unless the well
is thoroughly rinsed out. Otherwise, fish caught on the
next fishing trip and put into the live well will die
from bleach exposure.
The boat and trailer also should be
dried out regularly. That's what the DNR does with all
the watercraft employees use for work.
Ducks are also probably responsible
for the migration of zebra mussels from Lake Michigan
to inland waterways, said Marc Tuckman with the U.S. Environmental
Protection Agency Great Lakes National Program office
in Chicago. The young zebra mussels attach themselves
to the ducks' webbed feet and are transported to other
The adult zebra mussels need to attach
themselves to a solid surface, which is why they clog
water intake valves used by such industries as the steel
mills and Lever Bros. located along Lake Michigan's shores.
Most industries treat the water at their pumping stations
and near their intake valves in May and October with a
sodium chloride to kill the zebra mussels. Then before
the water is returned to the lake after the manufacturing
process, it is treated with sodium sulfide to neutralize
This process has cost Lake Michigan
industries millions of dollars in the last 16 years.
The threat to the environment of Lake
Michigan and other waterways is growing as the zebra mussel
Zebra mussels also attach to each other
and can colonize on docks, boat hulls, commercial fishing
nets and native mollusks such as clams. In fact, Tuckman
said, the mussels, which attach with a strong glue substance,
can cover native clams and kill them.
The freshwater mollusks, called Dreissena
polymorpha, are predators and eat protoplankton and the
aquatic animal Diporeia, which are both food sources for
"The zebra mussel takes out the bottom
of the food chain," Breidert said.
Zebra mussels are also thought responsible
for an outbreak of botulism that's killing birds around
Lake Erie and Lake Ontario, Tuckman said.
"They have huge colonies of zebra mussels,
some 1 meter across. They grow on top of each other,"
Tuckman said. "They are having a negative impact there."
To date, no such instances of botulism
related to zebra mussels have been reported in Lake Michigan.
In addition to chlorine bleach, zebra
mussels can be killed by specific bacteria.
However, they have only a few known
predators, including some diving ducks, freshwater drum,
carp and sturgeon. And these are not numerous enough to
control the population, according to the DNR.
"Zebra mussels are an invasive species,"
Breidert said. "They compete with other aquatic life for
food and they do a good job."