Zebra Mussel
(Dreissena polymorpha)
Biological Category
NY Legal Status
Species Type
Aquatic Invertebrate
DESCRIPTION
The zebra mussel is a small shellfish named for the striped pattern of its shell. However, color patterns can vary to the point of having only dark or light colored shells with no stripes. This mussel is typically found attached to objects, surfaces, or other mussels by threads extending from underneath the shells. Although similar in appearance to the quagga mussel (Dreissena bugensis), the two species can be distinguished by their shell morphology. When placed on a surface, zebra mussels are stable on their flattened underside while quagga mussels, lacking a flat underside, will fall over. When both zebra and quagga mussels occur in the same area, differentiation can be difficult due to the phenotypic plasticity seen in quagga mussels, and thus genetic identification is necessary at times.
Note: Research for these pages was generated from citations listed. References for specific statements available upon request.
Shell: The zebra mussel shell is triangular with a sharply pointed shell hinge edge. The most obvious identifier is the prominent dark and light banding pattern on the shell.
Size: It can grow to 5 cm, but most don’t exceed 4 cm.
This clam-like bivalve mollusk, commonly called the zebra mussel, Dreissena polymorpha, is a native of the Ponto-Caspian region of Eastern Europe and western Asia—the Black, Caspian, and Aral Seas, and the Ural River drainage. It was introduced into several European freshwater ports during the late 1700s; within 150 years Dreissena was found throughout European inland waterways. Dreissena was first found in the Great Lakes in Lake St. Clair in 1988, where it is believed to have been introduced as the result of the discharge of freshwater international shipping ballast water.
Zebra mussels are small (generally under 5 cm), with elongated shells typically marked by alternating light and dark bands. The mussels are generally found within 2 to 7 meters of the water surface but have been found as deep as 50 meters.
Eggs (as many as one million per season per female) are fertilized outside the body in the spring or summer. Larvae (veligers) are free-swimming for up to 30 days, being dispersed by currents. Juvenile mussels settle to the bottom and attach to suitable hard substratum (rock, wood, shells of native mussels, and human-made surfaces such as concrete, steel, fiberglass, etc.) by secreting durable elastic strands called byssal threads; if no hard substrate is available, zebra mussels will also attach to vegetation.
The mussel attaches itself to hard surfaces by byssal threads that emerge from between the valves through a byssal notch. Zebra mussels tend to attach themselves to hard surfaces along their flat edge, which is different from other similar species. Clusters and takes away from native mussels.
Once a population of zebra mussels has become established in a water body, there is very little to be done to remove them.
Prevention, therefore, is the best way to keep a water body clean of zebra mussels. Because they reproduce by spewing veligers into the water, zebra mussels are dependent on a current to spread their populations. This means that they can only move downstream in a river, and need a ride if they are to move further upstream.
Humans often aid them in their spread by transporting water from place to place. The microscopic veligers are invisible to the naked eye, and infected water transported in the bottom of a boat, inside a motor or via a livewell can readily become a new infestation if released into an otherwise clean river or lake. To prevent this, boaters must take care to drain their boats, motors and livewells before leaving a lake or river, wash their boat and trailer thoroughly, and allow it to dry for at least five days (the amount of time a zebra mussel can survive out of water) before taking the boat out again.
){kind=link}