Zebra mussel
| Zebra mussel | |
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| Species: | D. polymorpha
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| Dreissena polymorpha | |
The Zebra mussel (Dreissena polymorpha) is a bivalve mussel native to freshwater lakes of southeast Russia.
Reproduction
An adult female zebra mussel may produce between 30,000 to 1,000,000 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 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 warms.
Spread
In 1850 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.
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 1988, 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.
From their first appearance in American waters in 1988 they have spread to a large number of waterways, including the Mississippi and Hudson rivers, disrupting the ecosystem, killing the local unionid mussels, and damaging harbors, boats, and power plants. Water treatment plants were initially hit hardest because the water intakes brought the microscopic 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. Other examples are the round goby, alewife, and sea lamprey.
A popular inference made by scientists predict that the zebra mussel will continue spreading by ship to more rivers in North America since no natural predator resides in North America.
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. 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.
Food
Zebra mussels are edible, but most experts advise against eating any found in polluted waters since the mussels accumulate contaminants and toxins from the water as they filter. As long as they come from a clean body of water, zebra mussels can be used in any recipe calling for mussels. However, they are quite small, so it would take a lot of them for most recipes. Nathan Rules