Zebra mussel

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Zebra mussel

Scientific classification

Kingdom:	Animalia
Phylum:	Mollusca
Class:	Bivalvia
Subclass:	Heterodonta
Order:	Veneroida
Superfamily:	Dreissenoidea
Family:	Dreissenidae
Genus:	Dreissena
Species:	D. polymorpha

Binomial name

Dreissena polymorpha
Pallas, 1771

The Zebra mussel (Dreissena polymorpha) is a bivalve mussel native to freshwater lakes of southeast Russia.

1 Reproduction
2 Spread
3 Ecology
4 Anatomy
5 Similar Species
6 Effects of Zebra Mussels
7 External links

[edit] Reproduction

An adult female zebra mussel may produce between 30,000 to 400,000 eggs per year. Spawning usually begins in the months from late spring to early summer. 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 algal 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.

[edit] Spread

In 1827 zebra mussels were first seen in the Netherlands. Canals that artificially link many European waterways facilitated their early dispersal. Around 1920 the mussels reached lake Mälaren in Sweden.

Sign advising boaters on how to prevent zebra mussel spread on Titicus Reservoir in North Salem, New York.

Zebra mussels are currently causing serious problems in North America and Sweden, where they are considered an invasive species. Zebra mussels were first detected in the Great Lakes in 1986, in Lake St. Clair, located between Detroit, Michigan and Windsor, Ontario. They caused widespread damage in this ecosystem and had adverse economic effects on the communities surrounding the lakes. 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, which are stored in chain lockers when not in use, 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 1986 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, illustrating the costly effects of invasive species. 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.

[edit] Ecology

Zebra Mussel

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. 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. The additional organic material, coupled with increased habitat complexity, results in increased density and diversity of benthic organisms. Many scientists believe the zebra mussel colonization of the Great Lakes is concentrating biomass and nutrient energies in the benthic or bottom region of the lakes. This is biomass that was once available to other (often native) species. The full implications of zebra mussel colonization of the Great Lakes are still playing out and are not yet fully understood. There is growing evidence that the mussels are responsible for the decline of the native aquatic invertebrate Dioperia, which are an important food item for many fish in the Great Lakes. The changing populations of fish will bring their consequences, creating a cascade effect.

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.

[edit] Anatomy

Zebra mussels are relatively small in size, adults are 1/4 to 1 1/2 inches long[1]. They have tiny stripes down their shells, giving them 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 makes it very hard to remove the zebra mussel from the area it is attached to.

[edit] Similar Species

The quagga mussel is a similar species of the same genus from the Dneiper River drainage in Europe. It is similarly invasive as zebra mussels and has been out-competing and replacing zebra mussels in the Great Lakes.

[edit] Effects of Zebra Mussels

Zebra mussels are filter feeders. When they are in the water, they open up their shells to let detritus in. Some of the species that live in the waterway need this food to survive. Since Zebra mussels are an invasive species, the native species are starving.

Freshwater mussels are the most endangered species in the United States. Zebra mussels are greatly impacting the freshwater mussel population. Since both types of mussels are filter feeders and eat detritus in the water, zebra mussels tend to eat the food before the mussels, and cause them to die. However, zebra mussels also attach to the mussel's siphons on their posterior end. This causes them to not only starve, but also suffocate because they cannot get any dissolved oxygen in the water.

Zebra mussels also release a bit of phosphorus into the water. Phosphorus is a commonly used fertilizer that helps plants grow. When it gets into a freshwater ecosystem the plants grow rapidly. While during the daytime dissolved oxygen levels increase, at night while plants are undergoing respiration, dissolved oxygen levels decrease and hurt native species.

Zebra mussels are a great nuisance to many people. Since they have invaded 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.