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[Photo: USGS]
Zebra mussel
Dreissena polymorpha
Description: The zebra mussel is a small shellfish with a striped zebra-like pattern on its shell. It is similar in appearance to the quagga mussel (another invasive mussel) with brown or black stripes over a cream or yellow-colored shell. However, as the name "polymorpha" implies, the zebra mussel can take varied forms. The zebra mussel is 0.25-1.5 inches (0.6-3.8 cm) long with a D-shaped shell. It attaches to surfaces using an organ called a byssus, which consists of thread-like material.
Life History: Zebra mussels are filter feeders, feeding on mostly algae, but also detritus and zooplankton. They live from 3-9 years and reach sexual maturity at about one year of age (shell length 0.24-0.35 inches or 6-9 mm). Zebra mussels undergo external fertilization and spawn for several weeks as water temperatures reach 12 C or greater (May-Sept) and can spawn year-round in waters that maintain temperatures >12 C.
Habitat: Zebra mussels are a successful invader because they can tolerate a wide range of habitat conditions. They live in both freshwater and estuarine conditions and at temperatures ranging from 0-35 degrees Celsius (C). They can tolerate low dissolved oxygen conditions and can successfully attach to a wide variety of surfaces. Zebra mussels prefer a pH near 7.5, flow velocities of <2 meters/second and require calcium levels of >20 parts per million (ppm).
Distribution: Dreissena polymorphaare native to Eurasia (the Black, Caspian, and Azov seas). The species was first found in the Great Lakes in 1988. It was introduced to the Great Lakes in ballast water from a cargo ship originating from the Black Sea. Once introduced into the Great Lakes, the species quickly spread down the entire length of the Mississippi River. Zebra mussels have now been established in most major river systems and many inland lakes east of the Missouri River, with isolated populations as far west as California.
Status: Zebra mussels have rapidly spread due to their ability to effectively disperse as both juveniles (veligers) and adults. There are no native mussels which maintain a bysus in the adult form. This adult dispersal attribute has allowed it to quickly invade North America's waters, inflicting millions of dollars in damage from biofouling, and disrupting native ecosystems by significantly reducing phytoplankton abundance. Zebra mussels are considered one of the world's 100 worst alien invaders by the Invasive Species Specialist Group.
Resources:
Invasive Species Specialist Group
Minnesota DNR, Zebra Mussel Factsheet
NOAA, Aquatic Invasive Species Research & Outreach
USGS, Nonindigenous Aquatic Species
USGS, Southeast Ecological Center