| What are Zebra
Mussels?
Zebra Mussels (Dreissena
polymorpha) are small clam shells (1/2 - 2 inches) which attach to any
solid object with tufts of fiber called "byssal threads." They are native
to the Caspian Sea region of Asia, and were introduced into North America in
the mid 1980's via transoceanic ships that discharged ballast water into
Lake St. Claire, near Detroit. Tolerant of a wide range of environmental
conditions, zebra mussels have extended their range to parts of all the
Great Lakes and the much of the Mississippi River, and are beginning to
infest inland lakes as well.
These tiny mussels were first
discovered in North America in Lake Erie in 1988, most likely introduced
through the discharge of ballast water from a European vessel. In seven
years, the mussel has spread to all of the Great Lakes, and is beginning to
move inland as well. Biologists predict the worst of the invasion has yet to
come.
A single zebra mussel female
can produce in excess of 30,000 eggs, and the generations mature rapidly,
making it difficult to control them. A body of water may have no detectable
zebra mussels one year, and have its bottom covered with them the next.
Colonies can have from 70,000 zebra mussels per square yard, such as in
portions of Lake Erie, to the incredible 700,000 mussels per square yard
that have been found in some utility water intake pipes.
Zebra mussels feed by
extracting microscopic plant life from the water, robbing native organisms
of much needed food sources. A single adult mussel can filter a full liter
of water per day, every day of their life. During the peak populations in
Lake Erie, it was estimated that the entire volume of the Erie basin was
filtered through zebra mussels every single day.
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