Scientific Name: Dreissena polymorpha (Pallas, 1771) Common Name: Zebra Mussel

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Gabriela Post

Bio 205

Project: Zebra Mussel
Scientific Name: Dreissena polymorpha (Pallas, 1771)

Common Name: Zebra Mussel

Linnaeus’s system assigns to each species a two part Latinized name, or binomial. The first part is the genus to which the species belong. In this case: Dreissena. The second part refers to one species within the genus: polymorpha. With this system we can group species.

Scientific classification


















D. polymorpha

Binomial name

Dreissena polymorpha
Pallas, 1771

Kingdom: Animalia : Animal Kingdom (taxonomic kingdom comprising all living or extinct animals)

Phylum: Mollusca (gastropods; bivalves; cephalopods; chitons)

Class: Bivalvia (oysters; clams; scallops; mussels)

Species: Dreissena Polymorpha (inch long mollusk imported accidentally from Europe; clogs utility inlet pipes and feeds on edible freshwater mussels) Zebra Mussel

Zebra mussels, Dreissena polymorpha belong to the family Dreissenidae. It is a freshwater bivalve (shell is composed of two halves) mollusk (relative of clams), found in North America.

Where do they come from: Zebra mussels originated in the Balkans, Poland, and the former Soviet Union. They are native to the Caspian Sea, Black Sea, and Azov Seas of Asia. More specifically, from the north shores of the Black Sea, in the lower Dneiper or Bug River, near the Ukranian seaports of Kherson and Nikolyev. They were first discovered in the Ijral River in 1769. The mussels then spread throughout Europe in canals that were built in the 18th century. By the 1830’s mussels covered most of Europe and had invaded Brietain. They first appeared in North America, in 1886-1988 in Lake St.Clair, a small water body connecting Lake Huron and Lake Erie. Biologists believe that the zebra mussels were picked up in a freshwater European port in the ballast water of a ship and were later discharged into the Canadian side of Lake St. Clair. Therefore, they are not native to North America, but an invasive (introduced) species.

Zebra mussels are not the only freshwater bivalve molluscs that are found in North America, nor are they the only introduced species. Because of this, it is important to be able to distinguish between zebra mussels and members of the other two bivalve superfamilies that occur in North American freshwater habitats. The others being the Dreissena bugensis and Mytilopsis leucophaeata. These two are most likely to be confused with the zebra mussel.

Zebra mussels have a concave, or flattened bottom and an acutely angled shell margin. Both features provide additional stability for the attached mussel. If one places representatives from all three species on a flat dish, the zebra mussel will be the only one able to stand upright. The other two mussels have a more rounded bottom.


Zebra mussels mostly live in large rivers, lakes, or other bodies of water, such as the Great Lakes and the Caspian Sea. They flourish in warm weather and inland waterways in Canada and the United States. Zebra mussels have been known to attach themselves to places. Some zebra mussels are on the surface in/on docks, pipes, nets, and valves, but most live two to seven meters deep. Zebra mussels live in fresh and salt water, although the salt water has not been very salty. The ph of the water zebra mussels live in is between 7.4 and 8.5. Zebra mussels can be spread by many mechanisms, including water currents, angler’s bait buckets, and boaters’ bilge and livewells. Scientists currently believe that most inland lakes become infested by an introduction of adults rather than veligers (zebra mussel larvae).

Anatomy of the zebra mussel: Zebra mussels are small (<4cm/1.5in) about fingernail size, but can grow to a maximum length of nearly two inches. The smallest zebra mussel that has been found was fifteen millimeters, and the largest was fifty millimeters. They have a hard shell to protect their soft inner body. The shell is made from inorganic and organic materials that are from the water around the zebra mussels and leftover from the body. Cold, heat, food, and other things can change the shell production. If there is a crack or other damage to the shell, the zebra mussel can repair itself if the mantle tissue is still whole. The intestine gland becomes hyperactive and gives more calcium and other materials to the cells that are in the mantle and used in the repair process. Their shells characteristically have alternating light and dark bands (like a zebra) but may be entirely light or dark. They have a triangular, elongated shape. Zebra mussels have two holes: the excurrent and incurrent siphon for food. The adult feeds by filtering water through its siphons, and so zebra mussels, in a small way, clean out water. Zebra mussels also have a nervous, cardiovascular, and circulatory system.

Zebra mussels primarily eat algae. All the foods they eat are rich in calcium. Because there is no shortage of algae, zebra mussels can’t be hurt by starvation. They use calcium for many things, including repairing a damaged shell. Zebra mussels have a great impact on our lives. Some of the things they do are good. They are excellent filters of water. Because the water gets clearer, the sunlight can get lower and let more plants live. These plants provide shelter to some fish. Also many native fish, birds, and other animals eat young zebra mussels. Migratory ducks have changed their flight patterns in response to zebra mussel colonies. Lake sturgeon feed heavily on zebra mussels, as do yellow perch, freshwater drum, catfish, and sunfish. However, these native species do not feed heavily enough on zebra mussels to keep the population under control. Unfortunately, most of the changes zebra mussels have made to our lives are negative. Lots of birds have eaten them, gotten sick, and had trouble reproducing. Zebra mussels may dominate and end the diversity of species, especially native species, because of their rapid reproduction. When zebra mussels have come in contact with some species, they have practically killed them. For instance, they almost killed all native Unionid mussels. Some Unionids were found with 10,000 zebra mussels attached to them. For some reason, the zebra mussels prefer Unionids as a place to attach themselves to over stones or dead animals. The mapleleaf clam was also almost wiped out by zebra mussels. Even though the filtered water brings some positive effects, an adult zebra mussel filters up to a quart of water per day, which multiplied by millions of mussels means that the mussels may be filtering all the water in a lake or stream in a day. The animals and algae that are the food of zebra mussels are also the food for larval fish and other native species, so a large zebra mussel population may cause a decline in other animals, including native fish, mollusks, and birds. The filter- feeding activity of zebra mussels causes a related and frequently dramatic increase in water clarity in infested lakes and rivers.

Zebra mussels can severely affect native clams and mussels by interfering with their movement, growth, movement, respiration, and reproduction. For example, zebra mussels can colonize a clam shell to such an extent that the clam cannot open its shell to eat. Water and environmental agencies are working to protect endangered native species from the threat of zebra mussels. The primary emphasis of this effort is to education, so that boaters and fishermen do not inadvertently transfer mussel larvae from one water body to another. Unfortunately, zebra mussels do not have many predators here because they do not naturally exist in the North American environment. However, there are many things that eat the zebra mussel such as sturgeon carp, some diving ducks, and the round goby (who himself is a nuisance invasive species).Also birds, some crayfish, and other creatures. All these predators are still not enough to make a dent in the zebra mussel population.


Zebra mussels usually reach reproductive maturity by the end of their first year. Reproduction occurs through spawning when sperm and eggs are released into the water. Mating is encouraged by serotonin, a chemical in their brains. An adult female zebra mussel may produce between 30,000 to 100,000 eggs per year. Spawning usually begins in the months from late spring to early summer. The presence of food is the first factor that contributes to spawning. During this time a large population of algae will produce a pheromone recognized by zebra mussels. However, temperature is the main factor in determining when the spawning season begins. The ideal temperature for zebra mussel is 12 degrees Celsius and higher for spawning to start. If by any chance that above condition does not apply, then spawning may be suspended by that population. Spawning peaks at a water temperature of about 20 degrees Celsius. A fertilized egg results in a free swimming planktonic larva called a veliger. This veliger remains suspended in the water column for 1-5 weeks, and then begins to sink and search for a stable surface (e.g. rocks, aquatic weeds, water intakes) on which to live, grow, and reproduce.

Zebra Mussel Veliger Seaweed

Life Cycle

Zebra mussels live for four to five years. They start by crawling on the bottom of their habitat, but as they mature, zebra mussels find a more permanent habitat. When they turn two, zebra mussels begin to reproduce. As mentioned earlier, when it is about spring/summer, the process starts; Zebra mussels reproduce by broadcast spawning. The female excretes her eggs and the male fertilizes them with his sperm in the water. The eggs go through many stages before they become adults. These stages are:

Preshell Larva-the shell has not formed yet

Veliger Stage-the velum develops. Velum is the organelle used for feeding and swimming.

Straight-hinged Larva-the first time the shell is around the internal organs

Iimbonal Larva-the shell is not transparent anymore

Post-Veliaer Stage-time after the velum has finished developing

Pediveliger-has foot to help it move. The shell is thicker and whiter.

Planti grade-the last stage as a larva. The shell is not round; it has elongated. The siphons form

Settling Stage-the zebra mussel has finished making organs, gills, and siphons. It is now a juvenile and will be an adult when it can reproduce. It has also made byssal threads to attach itself to things. Only about 2% of all zebra mussels survive to adulthood. When a zebra mussel attaches to a hard surface, it is transformed into the juvenile stage. Then it develops the double shell which is typical of zebra mussels. A zebra mussel becomes an adult when it is sexually mature.

Human Impact

Humans have had many influences on the zebra mussels. After all, humans are responsible for bringing the mussels to the United States in first place. Since then, zebra mussels have made a significant impact and cost millions of dollars in damage. For the most part, trailered boats are to blame for the spread of the mussels throughout freshwater waterways all over North America. Although many companies now have ways to rid boats of these unwanted creatures, no permanent solution has been found. To find a solution, scientists need to know a lot about the internal anatomy and tissue structure of the zebra mussels. As of right now, very little is known. Right now industrial plants try to control the zebra mussels with equipment to preoxidize water at the point of intake, or use chemical treatments, mechanical controls, or filtration. There is no single, ideal solution.


The first DNA sequence data for dreissenid mussels has recently been obtained from two mitochondrial regions, cytochrome b and ND4. Analysis of DNA substitutions in these regions confirm species-level separation between the zebra and quagga mussels. The North American zebra mussel is genetically diverse, suggesting that the population was founded by relatively large numbers of divergent individuals. An extremely high level of genetic divergence was found in the cytochrome b gene, suggesting that variation within this species makes the zebra mussel one of the most genetically diverse known. For example, two individuals from the same location share only 82.3% of the sequence and are unique at 17.6% of the bases, suggesting a key factor in the mussels’ ability to rapidly colonize new habitats and adapt to new environments.

Sea Grant Zebra Mussel Report/ Biology and Life History 13

7/1/93 to 6/30/95

There is high genetic variability among Great Lakes zebra mussels. A second Dreissena species in the Great Lakes has been identified. There is a low level of genetic differentiation among Great Lakes zebra mussel population. Average heterozygosity among seven European populations examined was similar, indicating that little genetic variation was lost when zebra mussels were transported to North America.

In order to obtain control over the spread of the mussels, DNR (Department of Natural Resources) and other environmental agencies educate boaters and anglers how to clean their equipment and what to watch for. Also it is against the law to purposely move zebra mussels from one place to another, or even to just take them home. New sightings should be reported to the DNR.


DNR Department of Natural Resources, Michigan City, IN




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