Alien Invaders

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zebramusssel

Zebra Mussels

Alias: Dreissena polymorpha

Zebra mussels on pier legJust plain tough! Live Zebra Mussels cling to the leg of a pier several days after being removed from the water.

What Are They?

Zebra Mussels are a small bi-valve mollusk native to Eastern Europe.

Where Did They Come From?

Zebra Mussels were first discovered in the Great Lakes on June 1, 1988. It is widely believed that they were accidentally introduced to North America in the ballast water of a foreign vessel.

What Do They Look Like?

The word,”Polymorpha”is a latin word that means “many forms.” Zebra mussels can be white or cream-colored with jagged brown or black stripes or they can be all-white, all-black, or have stripes that go in opposite directions from their counterparts. Zebra mussels are members of the phylum Mollusca or mollusks. Mollusks are bivalve, meaning that they have two half-shells that are held together by a strong ligament.

Reproduction

The male zebra mussels release a cloud of sperm into the water while females release a cloud of eggs. A single female zebra mussel can produce 30,000 to 1,000,000 eggs a year. The fertilized eggs quickly develop into free-swimming larvae called veligers. These babies are smaller than a pin head. They feed on tiny phytoplankton in the water and begin to grow shells. The water current can cause veligers to travel great distances.

Around three to four weeks later, the shells of the veligers weigh enough to cause them to sink. At this point in time it is imperative that they attach to something or they will die. Any relatively stationary hard surface is sufficient. They attach themselves to rocks, wood, glass, metal, native mussels, a docked vessel, vegetation or even to each other. At this stage they are clear in color and cannot easily be seen.(Their presence on the hull of a boat can be detected by running a hand over its surface.) Not many of the babies actually survive to this stage but more than enough of the young zebra mussels do reach sexual maturity during their first year and are ready to continue the cycle, quickly increasing their population.

A single zebra mussel can filter about a liter of water each day. They leave the water clear, sometimes too clear. With increased water clarity and nourished by droppings from the zebra mussels, plants flourish and even grow in deeper water where none had existed before. This sometimes clogs lakes with huge amounts of vegetation and interferes with recreational boating

A single zebra mussel can filter about a liter of water each day. They leave the water clear, sometimes too clear. With increased water clarity and nourished by droppings from the zebra mussels, plants flourish and even grow in deeper water where none had existed before. This sometimes clogs lakes with huge amounts of vegetation and interferes with recreational boating

The presence of, zebra mussels alters the ecology of the lake in other ways as well. They feed on plankton and remove incredible amounts of food from the water. Bottom-feeding fish feast on the waste produced by the zebra mussels and the bottom-feeders number increases. But zooplankton and small fish which feed on plankton have much less to eat causing their numbers to decrease. Larger fish which rely on the small fish for food also decrease in number. The zebra mussels take food, space, and oxygen, causing the death of native mussels sometimes even growing on their shells, smothering them.

Zebra mussels also pile up on beaches when they die and wash up on the shore and begin to decay. Their shells are razor sharp and can easily cut the tender feet of swimmers.

The presence of, zebra mussels alters the ecology of the lake in other ways as well. They feed on plankton and remove incredible amounts of food from the water. Bottom-feeding fish feast on the waste produced by the zebra mussels and the bottom-feeders number increases. But zooplankton and small fish which feed on plankton have much less to eat causing their numbers to decrease. Larger fish which rely on the small fish for food also decrease in number. The zebra mussels take food, space, and oxygen, causing the death of native mussels sometimes even growing on their shells, smothering them.

Zebra mussels also pile up on beaches when they die and wash up on the shore and begin to decay. Their shells are razor sharp and can easily cut the tender feet of swimmers.

What Can be Done?

Drum Fish
Drum Fish

Freshwater drums (a type of fish pictured at right) and diving ducks eat zebra mussels, but don’t eat enough to control the zebra mussel population. Although there has been some evidence that some diving ducks are changing their migration patterns to munch on zebra mussels.

Zebra mussels seem to be able to survive everywhere, but they are rarely found in still water or fast-moving water. They also don’t do well in polluted water or at low oxygen levels. Summer water temperatures might also limit their spread.

Chemicals strong enough to kill zebra mussels will also kill the other animals living in the lakes. Scientists are searching for other ways to control their growth.

Zebra mussels are also just plain tough. Zebra mussel larvae can survive for a month in water with little or no food. Adults can survive a week or more out of water. They reproduce so rapidly that they out-compete other animals. With few natural predators, scientists are concerned about when and where the invasion will end. Once zebra mussels are established in a water body, very little can be done to control them.

For More Information:  http://www.ifishillinois.org/invasive/zebra.html