Zebra mussel
Dreissena polymorpha
The zebra mussel is a small freshwater mussel native to the Ponto-Caspian region. It is characterized by its triangular, often striped shell and its ability to attach to hard substrates using byssal threads. As a highly efficient filter feeder and invasive species, it has significantly altered aquatic ecosystems worldwide.
Details
Identification
Triangular shell shape; sharp edge on the ventral side; yellowish-brown base color with dark zigzag stripes; presence of byssal threads.
Social behavior
Forms extremely dense colonies (mussel beds) on rocks, pipes, and other mussels.
Diet
Actively filters phytoplankton, bacteria, and detritus from the water column.
Hunting strategy
Passive filter feeder via inhalant siphon.
Spawning substrate
Releases eggs and sperm into the open water; larvae (veligers) later settle on hard substrates.
Overwintering
Remains on the substrate; metabolism is significantly reduced at low temperatures.
Ecology
Ecological role
Ecosystem engineer; clarifies water but alters nutrient cycling through pseudofeces excretion and displaces native mussels.
Natural predators
Waterfowl (esp. tufted duck), benthivorous fish (carp, roach), crayfish.
Competitor species
Native unionids, invasive quagga mussel (Dreissena rostriformis bugensis).
Ecosystem service
Improvement of water clarity in lakes and rivers; serves as a food source for overwintering waterfowl.
Threats
Competition from the quagga mussel, predation by specialized birds, oxygen depletion in deep water layers.
Scientific profile
Profile
Distinguishing features
Sharp ventral ridge (unlike the rounded ridge of the quagga mussel); ventral side of the shell is flat; presence of byssal threads; short siphons; hinge without teeth.
Diet
Phytoplankton, detritus, bacteria, and small zooplankters.
Reproduction
Dioecious with external fertilization. The release of sperm and eggs is synchronized into the open water, typically occurring at water temperatures above 12-15 °C.
Role in food web
Important primary consumer and ecosystem engineer; links the pelagic zone with the benthos (benthic-pelagic coupling) through the excretion of pseudofeces.
Protection & threats
Main threats
Not threatened in most of its range; locally displaced by competition from the invasive quagga mussel (Dreissena bugensis).
Conservation measures
No conservation measures; management focuses on preventing further spread (e.g., cleaning of boats).