Audrey Rabalais | Fondriest Environmental
Scientific name: Dreissena polymorpha
Common name: Zebra mussel
Countries of origin: Southeast Russia, near the Black and Caspian Seas.
Invasion areas: Great Britain, The Netherlands, Czech Republic, Sweden, Italy, United States Great Lakes, Nevada, California, Louisiana and throughout the Midwest.
Zebra mussel facts
- Introduced to the United States in about 1986, the zebra mussel is thought to have hitched rides through ballast water in the bottom of ships traveling from Europe to the United States.
- They are named for the striped pattern on many of their shells.
- These destructive mussels are typically only the size of a fingernail and grow to a maximum length of two inches.
- They are often spread locally by attaching to smaller recreational boats that are not properly cleaned
- Zebra mussels can survive 3 to 5 days out of water
The problem with zebra mussels
Like typical invasive species, because zebra mussels have no natural predators, they outcompete native species for resources. Zebra mussels also can kill native U.S. mussels by attaching to their shells. Because the mussels are so populous, they often coat the bottom of lakes and rivers where aquatic insects normally burrow and forage. This has caused a sharp drop in native aquatic insect populations and those animals that feed on them (e.g., many fish) in some places, zebra mussels have intentionally been introduced because they can increase water clarity and transparency. By filtering large volumes of water, the mussels reduce the amount of algae in the water, resulting in clearer water. However, this efficient filtering reduces food resources (e.g., zooplankton) which reduce the number and health of fish. Additionally, because the mussels filter very effectively, they can concentrate toxins found in the water. When animals such as birds eat these contaminated mussels, they can die.
In addition to competing with other aquatic species for space and food, zebra mussels also create huge problems for water and lake managers. The mussels are renowned for their ability to latch onto poles, buoys, boats, beaches and all other equipment near the water in mass numbers. They clog water pipes and screens and can cause engines to overheat. They are also a danger to water recreationalists who can cut themselves on sharp shells.
Perhaps the most effective control of preventing the introduction of more zebra mussels is the ballast exchange program, often called the “swish and spit” method. Since 2006, U.S. and Canadian governments have required that ships flush out their ballast tanks with saltwater while out at sea. The saltwater is toxic to freshwater zebra mussels. This ballast water exchange program is believed to reduce the chances of further invasions. For example, as a result of the current program, it was reported in April 2012 that no new confirmed invasive species have entered the Great Lakes since 2006.
Other control measures include chemicals specific to zebra mussels that either kill adult species or prevent spawning and using low frequency magnetism to interrupt ions that would help form their shells.
Many areas infested with zebra mussels post signs asking recreational boaters to clean their boats thoroughly before leaving to prevent spreading them. Because the mussels can survive for days outside the water, boaters are believed to be the most common mechanism by which the mussels colonize new lakes and waterways.