Photo credit: Wen Baldwin, Lake Mead Boat Owners Association, Bugwood.org
Photo credit: Mike Quigley, NOAA, Bugwood.org
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Species at a Glance
The quagga mussel is a small, fingernail-sized, freshwater mollusk considered one of the most intrusive, prolific, and costly aquatic invaders in North America. Some feel this species is even more harmful than its close relative the zebra mussel (Dreissena polymorpha).
The shell is rounded, fan-shaped, and attached by a hinge. It is smooth and lacks ridges, although it typically has dark concentric rings that fade to a pale coloration near the hinge. While usually 3 cm (1.2 in) long, some individuals can reach up to 5 cm (2 in). The sticky threadlike projections called byssal threads are located toward the anterior end of the shell and help it to attach to other objects. Eggs hatch into round, microscopic larvae called veligers that free-float in the water column for up to five weeks before settling.
While the zebra mussel is similar, it is more “D”-shaped, with a prominent ridge on its ventral margin that allows it to sit upright. The quagga mussel is more rounded and would topple over if placed on its ventral margin. The midventral line is also straight in the zebra mussel while curved in the quagga mussel, and the byssal threads are located in the middle of the shell in the zebra mussel instead of at the anterior end.
The quagga mussel is found in both shallow, warm waters and deep, cool waters of freshwater lakes, reservoirs, ponds, quarries, and slow-moving or sluggish rivers. Its byssal threads attach to rocks, docks, cement, wood, and vegetation, but unlike the zebra mussel, it can also live and thrive directly on muddy or sandy bottoms. The quagga mussel can reproduce at low water temperatures as cold as 4-9°C (39-48°F).
One female can produce up to one million eggs in a breeding season. The free-floating veligers can be scooped up undetected and transferred in bait buckets, bilge water, and live wells. Because Dreissenid mussels can survive out of water for up to five days, they are easily transported to other waterways on recreational boating and fishing gear.
While native to the Black, Azov, and Caspian sea drainages, the quagga mussel first appeared in the Great Lakes in Lake Erie in 1989 in contaminated ballast water. It has since spread throughout all of the Great Lakes, the Mississippi River drainage, and many inland lakes. In the Mid-Atlantic region, the quagga mussel is established in New York and Pennsylvania.
Note: Distribution data for this species may have changed since the publication of the Mid-Atlantic Field Guide to Aquatic Invasive Species (2016), the source of information for this description.
Like the zebra mussel, the quagga mussel clogs water intake pipes and damages equipment at power and water facilities. It also harms fisheries, alters water quality, and increases the growth of harmful algae. It decreases food sources for native species by filtering large amounts of microscopic plants and animals from the water, and it can accumulate contaminants in its fatty tissues. Economic impact is in the billions of dollars.
Information for this species profile comes from the Mid-Atlantic Field Guide to Aquatic Invasive Species (2016).