Quagga mussel
Dreissena rostriformis bugensis
The Quagga mussel is a small freshwater bivalve mollusk that is considered a highly invasive species in Europe and North America. It is characterized by a rounded shell shape and variable striping, and unlike the zebra mussel, it can colonize soft substrates and thrive at great depths. Due to its enormous filtration capacity, it drastically alters aquatic ecosystems by shifting nutrients from the pelagic zone to the benthos. It also frequently displaces the previously established zebra mussel as well as native mussel species.
Details
Identification
Ventral side rounded (topples over when placed on its base), asymmetrical shell valves, usually paler base color than the zebra mussel, siphon openings often differ in size.
Social behavior
Sessile lifestyle; forms extremely dense colonies (mussel mats) on almost all available surfaces.
Diet
Filters phytoplankton, bacteria, and organic detritus from the water column.
Hunting strategy
Passive suspension feeder (filter feeder).
Spawning substrate
Releases gametes directly into the open water; larvae develop planktonically (veliger larvae).
Overwintering
Remains active year-round on the water body floor; high cold tolerance allows overwintering in deep water layers.
Ecology
Ecological role
Ecosystem engineer; increases water clarity, alters the food web by removing plankton, and is one of the few species to colonize soft substrates in the profundal zone.
Natural predators
Waterfowl (e.g., tufted ducks), benthivorous fish (e.g., carp, round goby), crayfish.
Competitor species
Zebra mussel (Dreissena polymorpha), native river and pond mussels (Unionidae).
Ecosystem service
No positive services known in invaded areas; filtration may visually improve water quality locally but harms fisheries.
Threats
No significant natural threats; controlled through mechanical cleaning of infrastructure.
Scientific profile
Profile
Distinguishing features
The most important feature is the convexly rounded ventral side, which prevents the mussel from standing stably on a flat surface. Furthermore, it lacks the sharp keel (carina) typical of Dreissena polymorpha. The byssal opening is small and located near the umbo.
Diet
Phytoplankton, microzooplankton, and organic detritus.
Reproduction
Dioecious; fertilization occurs externally in the open water. High reproductive capacity with multiple spawning events per year under suitable temperatures.
Role in food web
Primary consumer; acts as a link between the pelagic and benthic zones (benthic-pelagic coupling) and significantly clarifies the water.
Protection & threats
Main threats
Not threatened in Europe and North America; potentially threatened in its natural range (Ponto-Caspian) by habitat changes and pollution.
Conservation measures
No conservation measures required; management measures aim to prevent further spread (e.g., cleaning of boats).