Zebra mussel

Zebra mussel are a species of mussel known by the scientific name Dreissena polymorpha. Its is a tiny freshwater mollusk that is often the size of a fingernail. Getting its name from its striped-patterned shell, Zebra mussels are easily recognizable when seen. Though they are native to Eurasia, they quickly spread to the Great Lakes and other surrounding water systems via ballast water in ships during the mid 1980s. Because Zebra mussels are extremely small in their larval stage and are not visible to the naked human eye, they often latch onto boats, and unknowing seafarers transport them to new environments. Zebra mussels infest these environments rapidly because they have no natural predators there; in addition, a normal female Zebra mussel can produce up to one million eggs a year.

On average, one Zebra mussel can filter up to a gallon of water per day. Though this may seem benficial for the ecosystem, it actually does more harm then good. Because there is such a huge number of them, Zebra mussels can filter millions of gallons of water a day, thus depriving the other species of the resources necessary for survival. Though small, these mussels cause a major problem for many cities as they clog pipes, cover beaches, and kill the native species in the region. For many years scientists have experimented with methods of eradicating Zebra mussels, but unfortunately have been unable to find any means of removing the mussels offshore without harming the surround organisms.

Body Design


The zebra mussel is a small freshwater mollusk measuring 1/4 to 2 inches long, although most are about the size of a fingernail. Young zebra mussels are approximately the size of the diameter of a human hair and are thus invisible to the naked eye. If one touched these young mussels on a smooth area they would feel like fine sandpaper.

This organism gets its name from the pattern of stripes present on its shell. Although it is named after a zebra, not all zebra mussels have this exact appearance.

A zebra mussel's 'D'-shaped shell can have several different colors in a variety of patterns. Its coloration can range from yellow and light brown to almost black and white; some zebra mussels don't even have stripes at all. This variation in design accounts for the species' Latin name: polymorpha. A zebra mussel's shell consists of two valves connected by a ligament--a common characteristic of bivalves. These valves are comprised of three layers: the periostracum, the prismatic layer, and the nacre. The periostracum is the outermost layer and is secreted by the mantle--the inner lining of the mussel. The prismatic layer, which is composed of calcium carbonate crystals, is the second layer of the zebra mussel's shell. The nacre lies beneath this layer and is also comprised of calcium carbonate crystals secreted by the mantle. Another physical characteristic of the zebra mussel is its elastic hinge which allows the shells to open. To close its shells, the zebra mussel uses two muscles, called adductors, that are located in between the valves.

Zebra mussels posses a unique external organ called a byssus. The byssus is composed of many threads formed from hardened secretions of the byssal gland. The byssus allows the zebra mussel to attach itself to almost any hard surface--natural or manmade; zebra mussels are even able to attach to each other. It is the only freshwater mollusk with this capability. The zebra mussel, if removed from its position, can easily reattach itself and become secure once again. Part of the reason for this is the zebra mussel's advantageous shape. Because the bottom half of its shell is level, the byssus threads are able to easily pull the mussel flat against the surface it rests upon. Although it is similar to other mollusk species in its ability to fasten on to objects, the zebra mussel is unique in the fact that it also eagerly latches on to native mussels. This is a behavior known as bio-fouling. This behavior, along with its propensity to affix to other organisms and objects, results in complications within the zebra mussel's ecosystem.

Life Cycle
On average a zebra mussel usually lives to be about 2 to 3 years old. They go through three main periods of life: larva, juvenile, and adult. The larvae, called veligers, are the diameter of a strand of hair which makes them invisible to the human eye. They take 3 to 5 days to emerge. The larvae float around in the water for 3 to 4 weeks before they find a hard surface to attach to. They feed on algae from the rocks that they attach to.

A zebra mussel starts to change shape during its juvenile period. It begins to become more triangular. During the juvenile period the zebra mussels have the choice to detach themselves from the rock they are on and find a new surface to attach to or stay where they are and live there. The mussels have reached the adult period when they have reached sexual maturity which is usually around 2 years old. Zebra mussels are able to reproduce around age 2. A female zebra mussel can reproduce up to a million eggs every mating season. The baby mussels feed on phytoplankton and algae and filter through the water. They stack on top of each other on hard surfaces and they survive better when they are on other living surfaces. They grow to be about 6 to 45 mm which is about the size of a fingernail.

Ecology
Zebra Mussels can filter up to a gallon of water per day. A million zebra mussels filtering one gallon of water per day can end up filtering a whole lake which will use all of the other resources the other animal life will need to survive. A zebra mussel’s diet consists of algae and microscopic organisms. They are located in North America. Zebra mussels cause problems because their consumption of food is so great that it leaves little food for other species. This has caused a significant drop in populations or other species. Zebra mussels have taken over native species and completely killed off others. The zebra mussel is a kind of animal that hitches a ride onto different surfaces. For example if it ends up hitching a ride onto a hermit crab, it may end up weighing it down so much that the hermit crab would die from exhaustion. A major problem with the zebra mussel is their effect on boats. They can completely cover up and jam the engines or disable the boat altogether. When scientists use poison to kill the zebra mussel, the shells end up washing up on shore and slicing people’s feet. A huge issue with the zebra mussel is that the zebra mussel can clog anything. There are pipes that have to be removed because the small creature fits into them and latches on causing it to be clogged up. Almost anything that is under the surface of the water in an infested area has a chance to be overrun by the zebra mussel. To stop the mussels people have to use a specific poison to kill the mussel, but a major problem with this method is that they don’t know whether or not the poison is killing different animals and what animals are being killed.

Methods of Distribution and Eradication


Though native to Eurasia, the Zebra mussel has rapidly spread to many regions of the northern United States. Introduced during the mid-1980s, Zebra Mussels now inhabit all of the Great Lakes, many states’ rivers (mainly the Hudson, Illinois, Ohio, Arkansas, Tennessee, Mississippi, and St. Lawrence Seaway), as well as inland waterways. By traveling by ballast water (water in ships to assist in retaining stability while at sea), zebra mussels venture to foreign environments. Many scientists have come to a conclusion that approximately “as many as 3,000 exotic species per day are transported in ships around the world” Zebra mussels also transport themselves by attaching to the hulls of boats or in motor compartments; they are then either scraped off accidently or fall off Once in the water, they are distributed via currents where they eventually find new places to attach themselves and reside. Female Zebra mussels are another contributing factor as to why they have spread so rapidly and so efficiently. One female alone can produce up to one million eggs over the course of a year. The eggs soon begin to develop into larvae, and at about three weeks, the young Zebra mussels attach themselves onto solid objects. Due to the lack of predators, Zebra mussels thrive in their newfound habitats and swiftly outcompete the indigenous species that live there. Zebra mussels continue to repopulate and spread, making it difficult to eradicate them.

For many years, scientists have been puzzled as to how to remove Zebra mussels from the bodies of water in which they have made their new home. Along with rivers, lakes, and other waterways, Zebra mussels have also clogged up many pipes and residential water systems. Researchers have concluded that the best solution to this problem is to abolish Zebra mussels before they enter difficult places to access. Removing them before they can attach and grow eliminates many problems when cleaning them out. For onshore colonization (such as pipes and other inland water systems), the use of chlorine injections has been used to assist in killing Zebra mussels in all stages, from larvae to full-grown adult. This does not mean, however, pouring chlorine into water systems. It merely means adding a small amount of chlorine to a pump where the water intakes, before it is filtered and cleaned. Some copper mesh screens have also been utilized to keep Zebra mussels from entering systems (Copper, before it forms a green oxide surface layer, apparently repels Zebra mussels). These screens, though seemingly effective, still collect silt, algae, and other debris--and are therefore not as beneficial as previously thought. Other methods of filtration for pipes include sand filtration, infiltration galleries, buried intakes, and specialized sand filters. Pipes are now being formed out of copper and other materials to try and discourage Zebra mussel infestation. Other techniques used to eradicate Zebra mussels from pipes include running a plumber’s snake through the pipe, suffocating the mussels by cutting off their source of water for some time (this usually involves sealing the pipe), and desiccation (drying the Zebra mussels out) by draining the water out and allowing the Zebra mussels to sit for a few days. Periodically running heated water through pipes has also proven effective in the fight against Zebra mussels. No solutions to this date have been found to eliminate Zebra mussels offshore, however, without harming native species and organisms in the surrounding water.

Human and Economic Impact
Zebramusselscause problems because their consumtion of the food is so much that it leaves little food for other species.This has cause a great drop in other species with the infestation of these clams. Zebra mussels have taken over native species and completely extinct others. With zebra mussels being a "stick on" kind of crustation, they attach to various animals and can kill or harm the animal.

Invasive Species: Zebra Mussels
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