Asian clams(Corbicula fluminea) are native to Asia, Australia, and Africa. 

Distribution

The first documented occurrence of Asian clams in North America was along the Pacific coast in the 1920s. Some sources state that Chinese immigrants may have introduced it as a food source, though there is no direct evidence to support this. Another theory is that it was imported along with Gian Pacific Oyster. The exact mechanism of its introduction is unknown and can only be speculated. The USGS documents the first introduction of an inland waterbody in 1937 in the Columbia River near Knappton, WA. They are now distributed worldwide and in almost all 50 US states. 

A map of the distribution of Asian Clam. An interactive version can be found here. Source: USGS

Description

Asian clam is a small light-colored bi-valve mollusk about the size of a fingernail. The shell has distinct concentric ridges, or salculations, across its shell. The shells also have fine serrations or teeth on the inside, both lateral teeth, and cardinal teeth. The presence of these teeth distinguishes them from native fingernail clams. 

Biology & Habitat

Asian clams burrow into the bottom sediments of lakes and streams. They feed by filtering suspended particles from the water, most commonly phytoplankton. But also feed on detritus or dead organic matter by using their fleshy foot to pull material into their shell. They are most often found among sand and gravel. 

Adults are hermaphrodites capable of self-fertilizations; as a result, a single individual can start a new population. They can reproduce multiple times a year and live to an age of three to four years. Each individual can produce between 1,000 and 100,000 offspring each year. This makes them a particularly successful invasive species as multiple individuals don’t need to be introduced to start a new population, and their numbers can increase rapidly. 

Asian clam eggs mature into juveniles 4-5 days after fertilization. They become free-floating, utilizing a mucous pouch to aid in their dispersal. During this phase of their life, they can attach to plants, animals, boats, and other debris to further assist their dispersal. The juveniles eventually form into pediveligers which are shelled and have a foot. At this stage, they are about 0.25mm in size, making them nearly impossible to see. They reach maturity between three and six months of age, at which time they are 6-10mm in size, eventually maturing to 10-30mm in size. 

Threats & Impacts

Like other invasive mussels that grow to high densities, such as the zebra mussel, Asian clams can dramatically affect aquatic food webs. They are highly-efficient filter feeders that can significantly impact the phytoplankton community of a lake or pond, which is the base of the aquatic food web. This can result in increased water clarity, which can, in turn, affect light availability for aquatic plants, alter predator-prey relationships among fish, and alter water temperature.

High densities can also affect the nutrient cycling in a lake. Moving nutrients, especially inorganic forms, from the water column to the substrate. The increased nutrients, coupled with increased light availability, can increase aquatic plant growth.  

When large masses of Asian clams die, nutrients can be released into the water column, spurring algal growth. As bacteria decompose, their bodies dissolved oxygen can become depleted in the water column, affecting fish and other aquatic organisms. 

It is worth noting that the actual ecological impacts of Asian clams are poorly understood. More research is needed to understand the effect that they have on aquatic ecosystems. 

Spread Prevention

The best way to avoid the adverse effects of Asian clams is to prevent their introduction into new lakes and ponds. Recreational boats and trailers are an essential vector for spreading this invasive species. Following the Clean, Drain, Dry principles is vital whenever launching or retrieving your boat from a lake or pond. 

1. Clean all dirt, debris, and plant matter from your boat, trailer, fishing equipment, and other water-related gear.
2. Drain the bilge, engine, and all compartments of water.
3. Dry your boat for at least five days before launching in another waterbody.

Because the juvenile forms of Asian clams can be nearly impossible to see, you should visit a boat wash or decontamination station if they exist in your area. These stations clean both the exterior and interior of a boat with high-pressure hot water, which will kill juveniles. 

Control Methods

There is little that can be done to control Asian clam once it becomes established in a lake or pond. There have been some efforts to control their populations by using a benthic barrier, but this is not a widespread management practice. This underscores the importance of preventing the spread of this species. 

Common Native Look-A-Likes

Asian clam is most often confused with native fingernail clams. The main difference between the two is that Asian clams have two different sets of teeth located inside their shell. Fingernail clam shells are also smooth, whereas Asian clams have distinct ridges. 

Taxonomic Information

• Kingdom: Animalia
• Phylum: Mollusca
• Class: Bivalvia
• Order: Veneroida
• Family: Corbiculidae
• Genus: Corbicula
• Species: Fluminea

Frequently Asked Questions