Invasive Species: The Invasive Zebra Mussel

The Invasive Zebra Mussel

ABSTRACT

Many things can disrupt and alter ecosystems. Huge benefactors of disrupting ecosystems are invasive species. Invasive species are non-native organisms alien to the ecosystem. They are capable of invading aggressively into a habitat and take over the resources including sunlight, food, water, nutrients and space. Usually and most likely their invasion causes economic or environmental harm or harm to human health. Invasive species can be plants, animals or any other living organism whose introduction is primarily by the means of human actions. There are a limited amount of natural resources in an ecosystem so the invasive species and the native species compete for these resources. The native species have predators that check their population while the invasive species do not, so therefore the invasive species out-competes the native species.

The invasive species are harmful for native systems and time and money should be invested to prevent these species from spreading and damaging systems that they are not native to. Strict rules for environmental conformity are necessary and good. Much more needs to be done to protect our planets and its biodiversity from the invasion of alien species. When non-native species from other ecosystems are introduced, they can upset that balance and bring harm to the established plants and animals, and the whole ecosystem. Non-native species come from somewhere else and they are not natural to the ecosystem they have been introduced to. They may be harmless and beneficial in their natural surroundings, but they can totally devastate different environments. Established ecosystems have developed their own natural balance and controls over time, and the plants and animals within those systems find this balance suitable for survival, or they have been able to adapt in order to survive within those conditions. When alien species enter into an ecosystem, they can disrupt the natural balance, reduce biodiversity, degrade habitats, alter native genetic diversity, and further jeopardize endangered plants and animals. When there are no established natural controls, such as predators to keep the non-native harmful species in check, there can be a population explosion of the invasive non-native species causing an ecological disaster.

This final project focuses on one species, the zebra mussel, which is found in and around the Great Lakes in the northern United States. I studied research projects from the Michigan, Ohio, Pennsylvania, New York, and Rhode Island Sea Grants; as well as, independent research conducted at Ohio State University, Michigan State University, and the University of Michigan. Throughout the research I conducted I can conclude that the invasion of this invasive species poses a deliberate threat to the ecosystem in and around the Great Lakes and its tributary rivers and lakes. This project focuses on the introduction, biology, multiplication, control, and eradication of the zebra mussel.

Zebra mussels (Dreissena polymorpha) were first discovered in the Great Lakes region in 1988. Within one year, zebra mussels had colonized the surfaces of nearly every firm object in Lake Erie. Numerous populations are now well established in all of the Great Lakes and are rapidly spreading through the lakes tributaries. This includes spreading to the St. Lawrence River, the Hudson River, the Mississippi River, and the Ohio River, just to name a few. Zebra mussels have also been reported in several inland lakes as well, including Lake Wawasee in Indiana, Indian Lake in Ohio, and Kentucky Lake in Kentucky. (Snyder, 1989) Ultimately zebra mussels will colonize most lakes and rivers in Canada and the United States, unless we find ways to control them.

Over more than 200-years, these two-inch-long, gray striped mollusks extended from their habitat in the Aral, Black, and Caspian seas and the rivers feeding them to the waters of Western Europe. In German-speaking Europe their rapid spread earned them the name Wandermushcel, meaning wandering mussel. (Tenner, 1996) By the early 19th century they had turned up in England, but not until the late 1980s were they able to join the immigration to the United States. During the late nineteenth century, the practice of taking on harbor water as ballast accelerated the worldwide dispersal of marine organisms and introduced them to places they had not been before. Zebra mussels, especially, have been unique in their ways of traveling. When they are transported in the ballast water they are nearly invisible, once expelled have a huge range of dispersion, and cause immediate destructiveness.

The successful introduction into of zebra mussels into the Great Lakes probably occurred in 1986 when one or more transoceanic ships discharged ballast water into Lake St. Clair. The fresh water ballast, picked up in a European port, must have contained zebra mussel larvae (veligers) and possibly juveniles. Adult mussels may have joined in the journey, but would have had to have been carried in a sheltered, moist environment, such as sediment incrusted anchors or chains. (Rice, 1999) Marine scientists are not sure why the mussels spread so much more rapidly in the United States then in nineteenth-century Europe, but studies suggest that it is due to the temperate, plankton-rich Great Lakes.

The mussel's reproductive cycle is one key to its rapid spread and high abundance. Zebra mussels' egg production begins when water temperatures warm to about 54⁰ F, usually early May in Lake Erie and last until the water cools below 54⁰ F, usually October. (Snyder, 1989) A fully mature female mussel will produce approximately 500,000 eggs per season. Eggs are fertilized outside the mussel's body and within a few days develop into free-swimming larvae (veligers). It is during this stage that the mussels attach to a solid surface, if not they will die. Despite the huge numbers of Zebra mussels, most fail to attach to a surface and die off. Those that find a hard surface quickly attach themselves and grow into the typical, double-shelled mussel shape. (Snyder, 1989) Zebra mussels grow rapidly, about an inch, in their first year adding another inch in their second year. Their lifespan can be upwards of three years in U.S. waters, but the average is less than that.

Zebra mussels grow a tuft of fibers known as a byssus, or byssal threads, from a gland in the foot. The thread protrudes through the two shells and this is what the mussel uses to attach themselves to hard surfaces. Usually once a mussel attaches to a surface it stays there for its entire life. (Napela, 1993) Juvenile mussels can break away from their attachments and grow new, buoyant threads with allow them to drift in currents and attach to ne surfaces.