Asian clam
Corbicula fluminea
The Asian clam is an invasive freshwater bivalve characterized by its triangular, thick shell with prominent concentric ridges. Its color ranges from yellowish-green to dark brown, often featuring a purple tint on the inner shell surface. It prefers sandy or gravelly substrates in rivers and lakes, where it can reach extremely high population densities.
Details
Identification
Prominent concentric ridges, nearly triangular shape, yellow-brown periostracum, often purple inner shell surface.
Social behavior
Often forms extremely dense mass aggregations with up to several thousand individuals per square meter.
Diet
Filters phytoplankton, bacteria, and organic detritus from the water column.
Hunting strategy
Passive filter feeder using inhalant siphons.
Spawning substrate
Hermaphroditic; larvae are brooded within the gills of the parent.
Overwintering
Remains in the sediment; however, it is sensitive to prolonged frost and temperatures below 2°C.
Ecology
Ecological role
Competes strongly with native mussel species for food and habitat; alters nutrient cycling.
Natural predators
Water birds, fish (e.g., carp, bream), muskrats, and crayfish.
Competitor species
Native unionid mussels (Unionidae), zebra mussel (Dreissena polymorpha).
Ecosystem service
Water clarification through high filtration rates; serves as a food source for various predators.
Threats
Winter cold spells, oxygen depletion in sediment, extreme pollution.
Scientific profile
Profile
Distinguishing features
The most important feature is the coarse, regular concentric ridges (approx. 1-3 ridges per mm in adults). Unlike native Sphaeriidae, the lateral teeth of the hinge are distinctly finely serrated. The shell is significantly more massive and heavier than that of native fingernail clams.
Diet
Phytoplankton, bacteria, and fine organic detritus from the water column and the sediment surface.
Reproduction
Hermaphrodite (simultaneous hermaphroditism) with the ability for self-fertilization (androgenesis). Eggs are brooded in the gills (marsupium) until they are released as fully developed juvenile mussels (pediveligers).
Role in food web
Invasive ecosystem engineer. Competes with native mussels for food and space. Serves as a significant food source for specialized fish species and waterfowl.
Protection & threats
Main threats
Not threatened in Europe; local populations can collapse due to extreme cold events (below 2°C) or oxygen depletion in summer.
Conservation measures
No conservation measures required as it is an invasive species. Management measures aim to prevent translocation into previously uncolonized water systems.