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The 'Zebra mussel' (''Dreissena polymorpha'') is a bivalve mussel native to freshwater lakes of southeast Russia.
Zebra mussels get their name from the striped pattern on their shells, though not all shells bear this pattern. They are usually about the size of a fingernail, but can grow to a maximum length of nearly two inches. [1]

Contents

Reproduction

Spread

Ecology

Anatomy

Predators of Zebra Mussels

Effects of Zebra Mussels

Eradication

References

External links

Reproduction

An adult female zebra mussel may produce between 30,000 and 400,000 eggs per year. Spawning usually begins in the months from late spring to early summer by free-swimming larvae (veligers). The mussel may spawn during each of these periods. The presence of food is the first factor that contributes to spawning. During this time large algae populations produce a pheromone recognized by zebra mussels. However, temperature is the main factor that triggers spawning and mussels rarely spawn at temperatures lower than 12 degrees Celsius. If the water becomes colder, spawning may be postponed until the water has warmed.

Spread

Zebra mussel was found and described first in northern part of Caspian Sea and in the Ural River by Pallas in 1769. Grossinger reported it in Hungary in 1794. Kerney and Morton described the rapid colonization of Britain by the zebra mussel, first in Cambridgeshire in the 1820's, London in 1824, and in the Union Canal near Edinburgh in 1834.
^[1]
In 1827 zebra mussels were seen in the Netherlands at Rotterdam. Canals that artificially link many European waterways facilitated their early dispersal. It was recorded in Bohemia in Elbe river (now in The Czech Republic) in 1893^[2]. Around 1920 the mussels reached lake Mälaren in Sweden.

First reference in northern Italy is in Lake Garda in 1973^[3], in central Italy in Tuscany since 2003^[4].
Zebra mussels are considered an invasive species in North America and in most of Europe.
They were first detected in the Great Lakes in 1988, in Lake St. Clair, located between Detroit, Michigan and Windsor, Ontario. It is believed they were inadvertently introduced into the lakes in the ballast water of ocean-going ships traversing the St. Lawrence Seaway. Another possible — yet often neglected — mode of introduction is on anchors and chains, although this has not been proven. Since adult zebra mussels can survive out of water for several days or weeks if temperature is low and humidity is high, chain lockers provide temporary refuge for clusters of adult mussels that could easily be released when transoceanic ships drop anchor in freshwater ports.
From their first appearance in American waters in 1988 zebra mussels have spread to a large number of waterways, including the Mississippi, Hudson, St. Lawrence, Ohio, Cumberland, Missouri, Tennessee, Colorado, and Arkansas rivers disrupting the ecosystems, killing the local unionid mussels, (primarily by out competing native species for food) and damaging harbors, boats, and power plants. Water treatment plants were initially hit hardest because the water intakes brought the microscopic free-swimming larvae directly into the facilities. Zebra mussels are now believed to have cost North America billions of dollars in impacts each year.
A common inference made by scientists predicts that the zebra mussel will continue spreading passively, by ship and by pleasure craft, to more rivers in North America. Trailered boat traffic is the most likely vector for invasion into the North American west. This spread is preventable if boaters would take time to thoroughly clean and dry their boats and associated equipment before transporting these to new water bodies. Since no North American predator or combination of predators has been shown to significantly reduce zebra mussel numbers, such spread would most likely result in permanent establishment of zebra mussels in many North American waterways.

Ecology

Zebra mussels and the closely related and ecologically similar quagga mussel are voracious filter-feeding organisms. They remove particles from the water column, increasing water clarity and reducing pollution. Some particles are consumed as food and feces are deposited on the lake floor. Non-food particles are combined with mucus and deposited on lake floors as pseudofeces.
Lake floor food supplies are enriched by zebra mussels as they filter pollution out of the water. The additional organic material, coupled with increased habitat complexity, results in increased density and biodiversity of bottom dwelling benthic organisms. This biomass becomes available to bottom feeding species and to the fish that feed on them. The zebra mussel reduced eutrophication of Lake Erie^[1] and increased water quality.^[1] The catch of yellow perch increased 5 fold after the introduction of zebra mussels into Lake St. Claire.^[1]
Zebra mussels attach to most substrates including sand, silt, and harder substrates. Other mussel species frequently represent the most stable objects in silty substrates, and zebra mussels attach to, and often kill these mussels. This has eliminated many native mussel species from affected lakes in North America. This pattern is being repeated in Ireland where zebra mussels have eliminated the two freshwater mussels from several waterways, including some lakes along the Shannon.

Anatomy

Zebra mussels are relatively small in size, adults range from 1/4 to 1 1/2 inches long[2]. They have tiny stripes down their shells, hence the name Zebra Mussels. Zebra Mussels have a D-shaped shell. They attach to things with strings coming out of their umbo on the dorsal surface (side with the hinge). These strings are called byssal threads and make it very hard to remove the zebra mussel from the area it is attached to.

Predators of Zebra Mussels

There are a number of natural predators of zebra mussel. Zebra mussels have high nutritional value (Walz, 1979) and are consumed in large quantities by crayfish, waterfowl and in smaller quantities by muskrats. The nutritional value changes seasonally, particularly in terms of protein and carbonate content.
Crayfish could have a significant impact on the densities of 1 to 5 mm long zebra mussels. An adult crayfish consumes an average of nearly 105 zebra mussels every day, or in all about 6000 mussels in a season. Predation rates are significantly reduced at cooler water temperatures.
Several species of fish consume zebra mussels. Of these, roach seems to have the most significant impact on mussel densities. In some Polish lakes the diet of the roach consists almost exclusively (~95%) of zebra mussels (Stanczykowska, 1977). Despite all this, it seems that fish do not limit the densities of zebra mussels in European lakes.

Effects of Zebra Mussels

Zebra mussels are filter feeders. When they are in the water, they open up their shells to let detritus in.
Zebra mussels are a great nuisance to many people. Since they have colonized the Great Lakes, they have covered undersides of docks, boats, and anchors. They have also spread into streams and rivers across the country. In some areas they completely cover the substrate, and even cover other freshwater mussels. They can also grow so close together that they block off pipelines, impacting water intake pipes used by cities for their water supply, or by hydroelectric companies for power generation.
Zebra mussels and other non-native species are credited with the increased population and size of smallmouth bass in Lake Erie. [3] They also cleanse the waters of inland lakes, resulting in increased sunlight penetration and growth of native algae at greater depths. This can prove beneficial for fish.

Eradication

In 2006, the Virginia Department of Game and Inland Fisheries eradicated the zebra mussel population of Millbrook Quarry in western Prince William County by raising the concentration of potassium chloride to 100 ppm. [4]

References

1.

2.
Do Čech zavlečená slávka: ''Dreissena polymorpha'' Pall., , F., Blažka, Vesmír, 1893

3.
Dreissena polymorpha (Pallas) nuovamente in Italia. (Bivalvia, Dreissenidae), Giusti F and Oppi E, , , Mem Mus Civ St Nat Verona, 1973

4.
New records of ''Dreissena polymorpha'' (Pallas, 1771) (Mollusca: Bivalvia: Dreissenidae) from Central Italy, Elisabetta Lori and Simone Cianfanelli, , , Aquatic Invasions, 2006

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External links

★ Zebra Mussel on National Atlas

★

★ Dreissina FAQs

★ http://nationalatlas.gov/articles/biology/a_zm.html

★ 100th Meridian Initiative

★ U.S Federal Stop Aquatic Hitchhikers Campaign

★ BBC News: Lough Invasion Being Investigated

★ The Zebra Mussel Page

★ Invasive Species: Aquatic Species - Zebra Mussel (Dreissena polymorpha)

★ USA CoE Zebra Mussel Research Program

★ Zebra Mussel Watch

★ UMESC Invasive Species - Zebra Mussels

★ "What is the zebra mussel doing to Lake Michigan?", ''The Straight Dope,'' 22 September 2006.

★ ISSG

★ http://www.ehsni.gov.uk/zebra_2.pdf Zebra mussel in N.I.