The Effects of Zebra Mussels
The zebra mussel (Dreissena polymorpha) is an aquatic invertebrate that has invade much of the eastern United States. It is native to southeastern Europe and southwestern Asia; specifically, the Aral Sea, the Black Sea, and the Caspian Sea. It is believed that zebra mussels were first introduced to the United States around 1985, via accidental introduction from ships (Strayer, 1999). The initial place in which zebra mussels were introduced to U.S. waters was at Lake St. Clair, near Detroit, Michigan. Additionally, it has been shown that zebra mussels are probably more abundant in lakes than rivers (Strayer, 1999). |
The increased invasion of zebra mussels (1988-1997) |
During their larval stage, zebra mussels mostly feed on small phytoplankton. When they reach maturity, they feed on zooplankton, bacteria, and detritus, in addition to the phytoplankton (Strayer, 1999). Populations of zebra mussels can be very dense, and thus can have devastating effects on an ecosystem. For instance, zebra mussel populations can range from 100 to 10,000 per square meter over an entire river or lake (Strayer, 1999). Thus, they can have a drastic effect on phytoplankton and zooplankton populations (Mills et al, 1996). Zebra mussels are also detrimental to many mollusk populations. Most zebra mussels tend to attach themselves directly to the shells of unionids (types of mollusks) and other mollusks, in a method called direct fouling (Strayer, 1999). This method seems to hinder the locomotion of the unionid causing it to expend more energy for movement. Thus, many of unionid mollusks species suffer great declines as a result of this method. For instance, in Lake Erie, almost all unionid species were eliminated due to zebra mussel infestations (Strayer, 1999). Additionally, zebra mussels can still be detrimental to mollusks even without direct fouling because they feed on phytoplankton, which is also a large food source for many mollusks (Strayer, 1999). |
Currently there are no promising methods for removing the invasive zebra mussels from these habitats. Although zebra mussels are preyed upon by other animals such as crayfish, blue crabs, turtles, and diving ducks, none of its predators have ever had a drastic effect on their overall population (Strayer, 1999). Other conservationist efforts have concentrated on saving unionid species rather than eliminating zebra mussels. For instance, some have hypothesized that zebra mussel populations may crash for a period of time following their initial invasion. Thus, it has been suggested that some unionids be removed from their habitat during the initial zebra mussel invasion, and then reintroduced after the zebra mussel population has crashed (Strayer, 1999). This method has been experimented with, but there has not been much success. Overall, if new methods for controlling zebra mussels are not found, it is likely that the unionids species in the heavily infested lakes and rivers of the eastern United States will all be lost (Strayer, 1999). |
