Common Name: Zebra Mussel

Scientific Name: Driessenia polymorpha

Classification:

Phylum or Division: Mollusca
Class: Bivalvia/Heteroconchia
Order: Veneroida
Family: Dreissenidae
Subfamily: Dreisseninae

Identification: Zebra mussels are found attached to submerged objects such as boat bottoms, dams, and power equipment.  They are the only fresh water mussel found clustered like this.  Adults are about 1 inch long and can reach 2 inches.  They have alternating wavy dark and light bands of green/black/brown and yellow/cream/white respectively.

Original Distribution: Native to the Caspian Sea and Eastern Europe, by the 1830's the zebra mussel had expanded through shipping canals to most of Europe and Britain.

Current Distribution: Throughout the Great Lakes and Ontario and Quebec, Canada.  Down through the Missisippi and all major tributaries like the Ohio and Arkansas Rivers.  Eastward to Minnesota and westward to the Hudson.  Throughout the upper midwest.

Site and Date of Introduction: Introduced in 1985 to the Great Lakes region.

Mode(s) of Introduction: Released by ocean-going ships in infested ballast water.

Reason(s) Why it has Become Established: Zebra mussels thrive in the plankton-rich areas of Lake Erie and St. Clair.  They also are abundant reproducers, with females laying up to 1 million eggs per season, and reaching maturity at about 1 year.

Ecological Role: Zebra mussels filter up to 1 liter of water per day, clearing it of plankton.  They disrupt food chains and crowd out native mussels.

Benefit(s): The water purity is greatly improved.  The clarity in Lake Erie improved from 6-10 feet deep in the 80's to 10-17 feet in the 90's.

Threat(s): Ecological: The mussels severely disrupt food chains.  They remove the phytoplankton, starving the zooplankton which feed larval, juvenile, and other forage fish.  The prospects for fisheries in these areas are not good.  The filtering can have a down side - they bio-accumulate substances such as PCB's that can enter the food chain in dangerous levels.  Industrial: They clog water treatment and intake systems, causing slow-downs and stoppages.  Recreation: they affect docks and boat engines, sometimes causing overheating, and their sharp edges make beaches less desirable.

Control Level Diagnosis: This is probably a 'medium priority' closing in on 'high priority'.  Its affects are widely felt but not yet critical.  But, the speed with which its affects have been felt should be a cause of concern.

Control Method: Some predators exist, including the diving duck, and the scaup, canvasbacks, and old squaws.  Unfortunately, the duck has a migrating, transitory affect on the population, and the others are in low supply.  There is no know chemical agnet for control that won't damage other aquatic life.  They are susceptible to high temperatures and industry is experimenting with hot water outflows to control the population.  The most important control method is probably controlling the spread, by carefully cleaning boats and other recreational items before transporting.  Dry boating for a period of days and hot water are safe methods.  Chlorine has been tried, but is not suggested anymore since it's toxic.

Reference: Zebra mussel factsheet (DEP, PA); 'Zebra mussels in North America' (Ohio Sea Grant College Program)