Quagga mussel (Dreissena bugensis)

Synonyms: Dreissena rostriformis bugensis, Dreissena rostriformis

Common Names: Quagga

Description:

Quagga mussel (Dreissena bugensis) is a small freshwater mussel from the Ponto-Caspian region of Eurasia and a close relative of the zebra mussel [1][3]. It arrived in the Great Lakes in ballast water from ocean ships around 1989 and has since taken over much of the lakes, attaching to hard and soft bottoms and to boats, docks, and water pipes [1]. MISIN tracks it because it filters huge amounts of plankton out of the water, starves the food web, clogs water systems, and spreads easily on boats and gear [1][3].

Identification:

The quagga mussel is small ? its fan-shaped shell reaches only about 2 inches (4 cm) ? and it looks much like the zebra mussel, but with a few key differences [1]. Its shell is rounder and more fan-shaped, pale white to tan or brown, usually with darker curved rings; the pattern is softer than the bold zigzag stripes of a zebra mussel [1]. The clearest test is to set the shell down on its flat (hinge) side: a quagga mussel is rounded there and tips over, while a zebra mussel sits flat [1]. Like the zebra mussel, it anchors itself to surfaces with fine, tough fibers called byssal threads, often growing in dense clusters [1].

Quagga mussels can be found year-round, since adults stay attached to surfaces. Check boat hulls, motors, anchors, ropes, docks, and water intakes, and look for the small striped or ringed shells encrusting rocks and structures, especially after a boat has been in infested water [1][3]. Unlike the zebra mussel, the quagga thrives in colder, deeper water and on soft, muddy bottoms, so it can occur far from shore and at great depth [1].

At-a-glance cues:

1. Small fan-shaped shell up to about 2 inches, pale with darker curved rings [1]
2. Rounded on the hinge side, so it tips over instead of sitting flat (unlike the zebra mussel) [1]
3. Attaches to hard and soft surfaces with fine byssal threads, often in dense clusters [1]
4. Encrusts boats, motors, docks, rocks, and water pipes [1][3]

Habitat:

Quagga mussels live in fresh water ? lakes, large rivers, and reservoirs ? and they are remarkably adaptable [1]. They attach to hard surfaces like rocks, docks, and pipes, but unlike zebra mussels they also colonize soft sand and mud bottoms, and they tolerate colder water, living at depths of 400 feet (about 130 m) or more [1]. This lets them spread across far more of a lake, including deep offshore areas, than the zebra mussel can [1].

The quagga mussel is native to the Dnieper River drainage of Ukraine and the Ponto-Caspian region of Eurasia [1]. It reached North America in the ballast water of ocean ships entering through the St. Lawrence Seaway, was found in the Great Lakes around 1989, and has since colonized all of the Great Lakes and spread to other lakes and rivers [1]. It continues to expand into inland waters, largely carried on boats [1][3].

Reproduction:

Quagga mussels spread in two ways that matter to anyone who uses the water. Their young begin as microscopic, free-floating larvae (called veligers) that drift in the water and are easily moved in any water carried from an infested lake ? in a bilge, live well, bait bucket, or motor [1]. The adults attach firmly to hard surfaces, so they ride from lake to lake on boat hulls, trailers, motors, anchors, ropes, and gear ? overland transport on boats is the main way they reach new inland waters [1][3].

They also breed prolifically. Quagga mussels have separate males and females that release eggs and sperm into the water, and a single female can produce up to about a million eggs in a year, so a population can explode once established [1]. There is no seed-set window to target; the key is prevention ? clean, drain, and dry boats and gear so neither the larvae nor the adults are carried to a new waterbody (see Management) [1][3].

Impact and Damage:

Quagga mussels are not poisonous, but they affect people directly: their sharp shells encrust docks, boat hulls, ropes, and beaches and can cut bare feet, and they attach inside water-intake pipes at drinking-water and power plants, clogging them and driving up maintenance costs [1][3]. They can also foul boats and motors left in the water [1].

The deeper damage is to the lakes themselves. Quagga mussels are powerful filter feeders, and in huge numbers they strip plankton from the water ? the tiny plants and animals that form the base of the food web [1]. This can make the water look clearer, but it removes the food that native fish and other wildlife depend on, and the clearer water lets sunlight fuel nuisance algae and weeds [1]. The mussels also smother and kill native freshwater mussels by attaching to their shells, and they alter where nutrients go in the lake [1][3]. Because they clog infrastructure and disrupt fisheries, quagga and zebra mussels together cause very large economic and ecological damage across the Great Lakes region [1].

Similar species:

Zebra mussel (Dreissena polymorpha) is the closest look-alike ? a small striped mussel that also attaches with byssal threads and fouls boats and pipes. The easiest difference is the flat side: a zebra mussel sits flat on a table, while a quagga mussel is rounded there and tips over; zebra mussels also tend to have bolder dark-and-light zigzag stripes.

Asian clam (Corbicula fluminea) is another small invasive bivalve, but it is a rounded, ridged clam that burrows down into sand and mud and lives on its own, rather than attaching to surfaces with threads or growing in encrusting clusters like the quagga mussel.

Native freshwater mussels (family Unionidae) are much larger, with thick shells, and they sit half-buried and unattached in the bottom rather than clinging to rocks, docks, or boats. They are native and often protected, so a cluster of small mussels cemented to a hard surface is far more likely to be quagga or zebra mussels.

Monitoring and rapid response:

Signs to watch for:

1. Small fan-shaped mussels (up to ~2 inches) with pale, ringed shells that tip over rather than sitting flat, often in dense clusters [1]
2. Mussels encrusting boat hulls, motors, anchors, ropes, docks, and water-intake pipes [1][3]
3. Sharp small shells washed up on beaches [1]

What you can do:

1. Clean, Drain, and Dry every time. Before leaving a lake or river, clean all plants, mud, and animals off your boat, trailer, motor, anchor, and gear; drain all water from the bilge, live wells, bait buckets, and motor; and let everything dry completely ? ideally five days or more ? before entering another waterbody [1][3].
2. Never move water, bait, or aquatic plants from one waterbody to another, and throw unwanted bait in the trash, not the water [1].
3. Inspect docks, boat lifts, ropes, and equipment for attached mussels, and remove and dispose of any you find on land [3].
4. Report mussels found in a new lake or river (below), especially inland waters away from the Great Lakes [1].
5. Lake associations and crews should set up decontamination (hot-water, high-pressure washing) for boats and equipment moving between waters, monitor high-use access points, and coordinate with the state aquatic-invasive-species program [3].

When to call a professional:

1. A suspected new infestation in an inland lake, or mussels fouling a water-intake system ? contact your state aquatic-invasive-species program, since established mussel populations and infrastructure problems need specialized, coordinated management [1][3].
2. For chemical control options, contact a licensed applicator or your local cooperative extension office.

Report sightings to MISIN. Help track this species' spread by submitting observations through the MISIN web site or the MISIN mobile app (Android, iOS, Windows, and macOS). Photos at multiple angles paired with a precise GPS location are the most valuable data for confirming new occurrences and triggering rapid-response review.

Credits:

1. U.S. Geological Survey, Nonindigenous Aquatic Species Database. Quagga Mussel (Dreissena rostriformis bugensis) ? Species Profile. nas.er.usgs.gov
2. Michigan Department of Natural Resources. Invasive Species: Quagga Mussel. michigan.gov/invasives
3. Center for Invasive Species and Ecosystem Health (Invasive.org). Quagga Mussel (Dreissena bugensis). invasive.org

---