Originally introduced into the United States for from its native Southeast Asian waters by Chinese immigrants for the purpose of consumption, the Asian clam Corbicula fluminea has colonized many waterways in the northern hemisphere since it was first discovered in the Columbia River in Washington state in 1938. Since then, Asian clams have been introduced or dispersed into most of the United States. A recent study showed that climate change is a potential culprit for this rapid invasion as warmer waters are the preferred environment of the Asian clam.
Identifying Asian Clams
A bivalve that can grow as large as 5 cm wide and live up to 7 years, Asian clams can be identified by the presence of concentric rings on their shell. They occur in yellow and brown color morphs and the outer side of the shell can flake, revealing white spots. Though most mollusk species reproduce by broadcasting their gametes into the water, fertilization occurs in the inner gills of the Asian clam and offspring are not released until they are juveniles approximately 1 mm in size. Thus, Asian clam invasion can spread through the dumping of water from colonized sources as juveniles are still tiny but also have a high likelihood of survivorship and establishment due to the fact that they are more mature when they are released. Asian clams are often found at the bottoms of streams, rivers, ponds, and lakes, as well as man-made canals with sandy or muddy substrates.
Ecological and economic impacts
Asian clams are hermaphrodites, and reproduction by self-fertilization can occur, so just one individual could be all that is required to establish a new population in an uninvaded stream.
Asian clam excretions encourage algal growth which reduces water quality for native flora and fauna. Asian clams can aggressively colonize the bottom of waterways and can outcompete native species for space. Like another notorious bivalve invader, the zebra mussel, Asian clams can colonize and clog canals and pipes which results in monetary costs for mitigation.
A direct impact on population sizes may be possible through harvest and consumption, so check back on Wednesday for a tasty way to enjoy Asian clams!