Asian Clam (Corbicula fluminea, O. F. Müller, 1774)
Origin: Eastern Asia
Size: up to 5 cm
The Asian Clam is a freshwater bivalve but it can survive just as well on the upper side of the estuaries (salty and brackish water). The shell is strong with a triangle-oval shape, with visible concentric grow rings; the colour varies from the dark brown to yellow green (depending on the substrate).
The species occurs on a wide variety of habitats, rivers, lakes, reservoirs, and estuaries, and in different substrates (muddy, sandy, and rocky); it is high tolerant to the abiotic factors (salinity, temperature, pH), the only requirement is well oxygenated waters.
The sexual maturity of the Asian Clam is reached in the first year (meaning it can start reproducing), it is a hermaphrodite species (both male and female sex in the same individual) and can reproduce alone, although prefers cross fecundation; the larvae (young) are released in the water (in spring and autumn) and can disperse easily. This species is a water filterer, feeding on particles floating on the water column but also on organic matter in the sediment.
The introduction route of the Asian Clam is not well known, it appeared for the first time in the Tagus River in 1980 (first record for all Europe), in 1989 appeared in River Minho and Douro and in 2000 was colonizing several rivers and estuaries in Portugal. The transport on the ship’s hull’s or as bait for fishing are some of the possibilities of its introduction. Nowadays it is introduced in America and Europe.
The Asian Clam is a very problematic species causing ecological changes on the ecosystems (competition with native species, predation of larvae of other species enable then to reproduce, changing the nutrients cycle) but as well negative industrial impacts (blockage of water distribution systems).