So
What Is
So Bad About Zebra Mussels?
Ever since zebra mussels (dreissena
polymorpha)
showed up in the Great Lakes in the mid-1980s, a lot of people
have asked
"What do they do? Do they harm the environment?" And
the answers
depend on who you're talking to when you ask these questions. If
you're
a diver, the answer is they have vastly improved visibility
underwater.
Okay, so that's good, right? Well, no. Because while you're
enjoying the
clear view of your favorite wreck, almost microscopic baby zebra
mussels,
called velligers, are attaching themselves
to various parts of
your boat,
including your cool water inlets. When they colonize, your
intakes will
clog and your engine will overheat. Okay, so all you have to do
is rinse
the hull and other parts off while the boat's sitting on the
trailer in
the driveway and wash 'em down the sewer; end of problem, right?
Well, no.
Because they can survive for up to 21 days out of water, and
you've just
colonized the storm sewer system in your community. And oh won't
the local
sewer department love you for that!
How did they get
here?
As
far as anyone knows, one or several freighters in the mid-1980s
loaded
up with ballast water in the Balkans, taking zebra mussels with
it. When
it arrived in the U.S., it discharged its ballast water, along
with its
"stow-aways." Zebra mussels showed up in Lake St.Clair
around
1985 or '86. Since a female is capable of producing more than
30,000 eggs
in a season, they quickly spread to Lake Erie. By 1990, they were
invading
Lake Michigan, and a short time later, invaded the Chicago area
coastline.
The photo shows a boulder at about 40 feet in Lake Michigan just
off the
south side of Chicago. Zebra mussels cover almost the entire
surface.
How do they clean
the water?
Zebra mussels are
filter feeders.
They consume massive amounts of the particulate matter floating
around
in the lake, which is why underwater visibility is so much
better. One
tiny zebra mussel can filter one liter of water a day! Most
divers have
reported that they can actually see their dive buddies under
water!
Why not catch 'em
and cook
'em?
Yuck! Actually,
they're very
small and they accumulate biotoxins.
Are they just pesky,
or are
they harming the environment?
Researchers at the
Illinois/Indiana
Sea Grant Program say that indigenous creatures who feed on
phytoplankton
and zoo plankton may be losing their food supply. Studies have
shown changes
at every level of the ecosystem of infested areas. For example,
the decrease
of yellow perch in Lake Michigan may be due to zebra mussels.
Any economic
impact?
Various facilities
around Lake
Michigan have spent more than $120 million on the control and
clean-up
of zebra mussels. Because they thrive in cold, dark places, water
intake
pipes are ideal for their colonies. With the strong adhesive on
their bissel
threads, they stick like glue to the inside of the pipes. Great
Lakes utilities
have reported reduced pumping capacities and occasional
shutdowns. Also,
since they often attach to, and suffocate, larger mussels, the
mussel harvesting
industries in the northern Great Lakes areas have suffered.
Will they affect
drinking
water?
Some people have
noticed a
change in the taste of Great Lakes tap water. Because the water
is much
clearer, more sunlight is getting through to stimulate the growth
of algae,
thus affecting the taste, but not the potability, of drinking
water.
What about the
impact on diving?
While divers are
enjoying improved
visibility, what they're seeing is mussel encrusted wrecks. Many
of the
historic wrecks near Chicago's coastline are almost completely
covered.
Also, divers have to be cautious about coming in contact with
mussels because
of their hard, sharp shells. Damaged wet suits - and skin - is
not uncommon.
Can scientists come
up with
a way to get rid of them?
So far, nothing has
worked.
Prechlorination could be used on intake pipes, but this raises
concerns
about the negative impact on other organisms. Also, it wouldn't
get rid
of all zebra mussels, just those around intake pipes.
What about natural
predators?
Crayfish, carp, eels,
sheep's head
and some waterfowl prey on zebra mussels, but the reduction of
zebra mussel
populations in many areas is insignificant. For now, it looks
like they're
here to stay.
What can divers
do?
Be careful where you
clean
your gear. Zebra mussels can live up to 21 days our of water. If
you rinse
your gear in a sink or near a storm sewer, you could send live
velligers
into the storm sewer system. Use hot (104 degrees or above) water
or rinse
your gear out with a hose in an area away from sewers.
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