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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 begining 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. They most definitely are. Zebra mussels arrived in the Midwest about two years ago when an infested barge traveled from Lake Erie, down the Illinois River, to the Mississippi River. That single barge seeded the entire Illinois and Mississippi Rivers. Zebra mussel densities continue to increase at lock and dams on the upper Mississippi River. Densities at the uppermost portions remain relatively low. Densities range from 1 per every square meter at Lock and Dam 1 in St. Paul, Minnesota, to 11,432 per square meter at Lock and Dam 13 just north of Davenport, Iowa. Most of the Locks and Dams in between had densities greater than 1000/m2. The researches at the National Biological Service in Wisconsin say these numbers are up from last year.  A can pulled
off the river bottom.
Large numbers of zebra mussels can filter all of the water in a lake or stream, removing plankton (tiny plants and animals) that serve as food for larval fish, which in turn serve as food for larger fish. The plantion also is a vital food source for native mussels. When the zebra mussels filter the plankton out, a link in the food chain is broken, causing severe damage to native species. The hatching success of reef spawning fish such as walleye, sauger, white bass, and small-mouth bass may be reduced in zebra mussel infested areas.
Aquatic insects attach to rock substrates in streams and lakes and are important food sources for many fish. It is unknown what impact infestations of zebra mussels will have on their populations. Recent studies have shown that zebra mussels may mobilize toxic materials from the sediments into the food chain in two ways. First, when the mussels filter algae that has absorbed toxic materials, they either ingest the toxic materials, which accumulate and concentrate in the mussel's fatty tissue and is then passed on to fish and ducks that prey on mussels, or they release the toxins as pseudofeces waste, putting it back into water column. Also, zebra mussels provide a new mechanism of introducing toxins to the food chain, as amphipods that graze on the pseudofeces containing the toxins are then eaten by fish. Power plants and water treatment plants located on Lake Erie have experienced 20-30% reductions in their pumping ability due to zebra mussels clogging the intake pipes. They have spent up to $1 million a year on controlling and researching the zebra mussel. Since the mussels filter water so effectively, they increase the water's clarity. This in turn results in enhanced growth of aquatic weeds, which has led to taste and odor problems in drinking water supplies. This has necessitated in more expensive and aggressive water treatment procedures. Dense growths of zebra mussels on breakwalls, locks and dams, control structures, and intake ports of water cooled engines are causing concern. They are also known to increase the rate of corrison of iron and steel structures at the point of attachement. Commercial fishermen and clammers are begining to feel the effects of dense infestations of zebra mussels on native clam beds and fish spawning sites. Several formerly productive beds have already been decimated by zebra mussel growth. Zebra mussels attach to boat docks and boat hulls. They plug water intake ports, causing outboard motors to overheat. Huge deposits of dead zebra mussel shells can wash on beaches, causing foul odors and cutting bathers' feet with their sharp shells. In Lake St. Claire, the filtering action of zebra mussels has caused clearer water. More sunlight reaches the bottom and there is now more vegetation. Walleye are being replaced by other fish and may disappear because they are no longer reproducing successfully. Other formerly productive fisheries are also in decline caused by loss of food source and spawning grounds due to zebra mussel infestation. Lake- or river-wide control of zebra mussels is not feasible at this time. The European comunity has been unable to find a control after two centuries of infestation. In the Great Lakes, no chemical toxicant has been developed that is both feasible for widespread use and not toxic to other aquatic species. In some parts of Europe, large diving duck populations have actually changed their migratory pattern in order to forage on zebra mussel beds. In one case on the Rhine River, diving ducks and coots consumed up to 97% of the standing zebra mussel crop each year, but the high reproduction rates of the mussel replenished the population each summer. In North America, the species most likely to prey on relatively deep beeds of zebra mussels are scaup, canvasbacks, and old squaws. The problem is that populations of these duck species is very low--canvasbacks are so rare they are protected. Mallard ducks have also been found to forage on zebra mussels in shallower waters. Freshwater drum have also been observed to feed on the mussels, and yellow perch have been seen feeding on juveniles, mainly when they are detached and drifting. One approach to control that is being studied is to control the mussels by disrupting their reproductive cycles. The eggs are fertilized externally, so the male and female must release their gametes simultaneously. After release, the male's sperm is viable for only a short time, perhaps as short as only a few minutes. Disrupting the synchronization of spawning by males and females may effectively reduce the number of fertilized eggs. Researchers are studying the environmental and physiological cues that coordinate zebra mussel spawning activity. If you are a water recreationist- anything from a boater, angler, or a waterskier to a sailor or canoeist- there are some important things you can do to help prevent the spread of zebra mussels to non-infested waters. It is also illegal in many states and providences to transport exotic species. Boat Cleaning: bCompletely drain all water from your boat, motor, and trailer. Microscopic zebra mussel larvae can live in the water for many days. Wash everything using hot (140oF or hotter) water; pressure washers with hot water are most effective. Dry boats and trailers in the sun at least four days before use in uninfested waters. Areas to check and clean:
Other Important Checkpoints: Empty your bait bucket on land, never into the water. Never dip your bait or minnow bucket into one lake if it has water in it from another. And never dump live fish from one water body into other waters. |
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
Zebra mussels grow in thick mats on each other and other shells.
Colonies can suffocate freshwater mussel beds; they are expected to cause
the elimination of 8-10 species of native mussels. Some rocky areas
in Lake Erie are covered with a 10-inch deep layer of zebra mussel shells
(up to 90,000 per square yard). Any firm surface that is not toxic can be
colonized by zebra mussels- including boat hulls and motors, trailers, docks,
anchors, and rocky beaches. In times of low water, a band of zebra mussels
a few inches thick can be seen along the shores in areas of the Mississippi
River.
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