Description of Zebra Mussels
Zebra mussels are a type of small freshwater mollusk native to Eastern Europe and the former Soviet Union. According to the National Atlas of the United States, they were first discovered in 1988 in Lake St. Clair, a small body of water that connects Lake Huron and Lake Erie. These mussels have since become invasive in the United States and present a major economic and environmental threat to the Great Lakes region.
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Size
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Zebra mussels are normally about the size of a human fingernail–about 1/4 of an inch long. Some specimens may grow up to 1-1/2 to two inches in length. Zebra mussels are much smaller than native striped mussel species and have been known to cluster onto the shells of other mussels, clams and crayfish. According to the National Atlas of the United States, some native mussels have been colonized by more than 10,000 zebra mussels, preventing them from opening their shells to feed.
Pattern
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This type of mussel is named for its alternating yellow and brown stripes, which can be very bold in some specimens. However, not all zebra mussels have stripes. Some are almost entirely solid in color, while others appear variegated rather than striped. Size and shape are better indicators of zebra mussels than pattern.
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Life Cycle
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Zebra mussels may live up to four or five years and are capable of reproduction at two years of age. A female zebra mussel produces 30,000 to 1,000,000 eggs per year, only about two percent of which live to become adults. Young mussels are small, free-swimming larvae called veligers, which then go on to develop shells. At the age of two to three weeks, these creatures choose a firm surface, such as a rock, boat hull or even a crustacean, and attach themselves to it using their byssal threads. These are strong, silky fibers made from proteins secreted by the mussel. They are the only freshwater mussels that can adhere themselves to objects. If dislodged by a storm or other force, the zebra mussel simply chooses a new surface.
Feeding
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Zebra mussels are filter feeders and may filter as much as one quart of water per day. They eat algae and microscopic animals in the water and so may decrease the food supply available for native animals. Zebra mussel filter feeding has such a strong effect on the water that rivers and lakes infested with these creatures may suddenly become much clearer, signifying a drop in microscopic life.
Predation
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Some native North American animals eat zebra mussels, as well as migratory ducks, catfish, sunfish, yellow perch and lake sturgeon. Unfortunately, these native species don't feed heavily enough on zebra mussels to control the population. The mussels are not large enough to be appealing to humans.
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References
- Photo Credit lake image by Alison Bowden from Fotolia.com
