Chesapeake Bay Introduced Species Database


Corbicula fluminea

Common name(s):
Asian Freshwater Clam
The Asian Freshwater Clam Corbicula fluminea is native to Asia, Indonesia, Philippines and probably Africa and Australia. It was introduced in western North America by Chinese immigrants as food before 1924. It is now found throughout the Pacific, Mississippi, Gulf, Great Lakes, and Atlantic drainages. Its rapid spread suggests that there were multiple introduction pathways and entry points including ballast water, canals, fisheries, and the aquarium fish-bait trades. It arrived in the Chesapeake Bay watershed in the 1970s and is now very common in most freshwater tributaries. The introduction of such a rapidly reproducing filter-feeder has increased water clarity and provided a new food resource, but may also have far-reaching effects on food webs, nutrient and organic material transport to lower parts of the Bay, and on migratory birds and fish. In areas with high population densities they compete for food and space with native freshwater mussels.
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Economic Impacts

Impact:
Industry; Fisheries; Aesthetics; Habitat Change
Corbicula fluminea (Asian Freshwater Clam's) impacts on Chespaeake Bay tributaries were diverse and complex, owing to this species' rapid population growth and attainment of large biomasses. Many of its ecological impacts, on water clarity, benthic/pelagic partitioning of biomass, providing a new food resource, etc. have also had economic implications. Here, we focus on more direct economic impacts.

Industry - Corbicula fluminea caused fouling of nuclear and conventional power plants, by clogging water pumps and condensers, including Potomac River Steam Electric Station, Alexandria VA, and the 12th Street Generating Plant, Richmond VA, resulted in reduced efficiency, decreased output, and outages due to time required for cleaning (Diaz 1974; Potter and Liden 1986). C. fluminea also fouled municipal water treatment facilities, and other industrial facilities utilizing water from rivers(McMahon 1983).

Habitat Change - See 'Ecological impacts'.

Aesthetic - Die-offs and strandings due to floods and other causes produce bad odors (McMahon 1983), but C. fluminea grazing can increase water clarity (Cohen et al. 1984; Phelps 1994).

References - Cohen et al. 1984; Diaz 1974; McMahon 1983; Potter and Liden 1986; Phelps 1994


Economic Impacts Outside Chesapeake Bay

Impact:
Corbicula fluminea (Asian Freshwater Clam's) impacts on Chespaeake Bay tributaries were diverse and complex, owing to this species' rapid population growth and attainment of large biomasses. Many of its ecological impacts, on water clarity, benthic/pelagic partitioning of biomass, providing a new food resource, etc. have also had economic implications. Here, we concentrate on more direct economic impacts.

Negative impacts noted from different parts of North America include:

Corbicula fluminea caused fouling in irrigation canals including deposition of dead clams and shells, and increased sedimentation rates. This clam also clogged irrigation pipes (Isom 1985); interfered with riverbed gravel-mining operations (Diaz 1974), and fouled gravel aggregate which is used in cement. When cement is poured and begins to set, the clams burrow to the surface, causing the cement to become porous and structurally weakened (McMahon 1983).

Corbicula fluminea caused fouling problems in electric generating plants, and in water treatment and water-filtration plants, as well as many other industrial operations using river water (McMahon 1986). It caused shutdowns of a nuclear generating plant in AR in 1980. Overall costs of Corbicula to the electric power industry probably exceed $1 billion per year (Isom 1986). 'For facilities already in use, biofouling by C. fluminea continues to be an expensive and exasperating problem for which there are now no universally accepted remedies'( McMahon 1983).

Likely beneficial uses of C. fluminea include: as a bioassay or bioindicator organism, as a protein and calcium supplement in domestic livestock feeds; as a source of lime for poultry feeds and fertilizers; as a source of live and preserved bivalve material for commercial biological suppliers; as a clarifier for tertiary sewage treatment systems, removal of particulate organics (McMahon 1983), or as bait. In 1970, 2.2 million pounds were sold as bait in CA alone, at a value of 234,000 dollars (Isom 1986).

References - Diaz 1974; Isom 1986; McMahon 1983


Ecological Impacts

Impacts on Natives:
Herbivory; Food/Prey; Competition; Habitat Change; Toxicity
As a rapidly reproducing and spreading filter-feeder, Corbicula fluminea (Asian Freshwater Clam) has had potentially far-reaching effects on foodwebs within the tidal fresh region of estuaries (Phelps 1994), on the export of nutrients and organic material to lower parts of the Bay and sub-estuaries (Cohen et al. 1984), and on migratory birds and fishes feeding or breeding in the tidal freshwater region (Perry 1981; Phelps 1994).

Herbivory - In 1980, the biomass of C. fluminea in the tidal fresh Potomac was estimated to be sufficient to filter all of the phytoplankton of one stretch of the Potomac (Rosier Bluff to Hatton Point MD; River Km 160-165) every 3-4 days (Cohen et al. 1984). Ecological implications of this grazing are discussed below.

Competition - In tidal fresh estuaries of Chesapeake Bay, C. fluminea represented up to 90-95% of the bivalve biomass (Cohen et al. 1984; Diaz 1994), and represented a source of potential competition for food and space with native bivalves. C. fluminea reaches densities, biomasses, reproductive rates, and population filtration rates rarely reached by native molluscs (McMahon 1983). Effects of C. fluminea invasions on native bivalve populations appear to vary. Factors limiting C. fluminea's dominance include its lesser tolerance of extreme temperatures, low oxygen concentrations, and dessication compared to many native species (McMahon 1983). In an SC Coastal Plain stream, C. fluminea appeared to be restricted by substrate preference and was not affecting abundance of the native bivalve Elliptio complanata (Eastern Elliptio) (Leff et al. 1990). Competition for space with the sphaeriid Musculium partumeium (Swamp Fingernailclam) has been noted, and in some cases reductions in native unionid and sphaeriid populations have been noted (McMahon 1983). In the nontidal James River, Corbicula was thought to have virtually eliminated the native unionid Pleurobema collina (James River Spinymussel), which formerly ranged from Richmond to the headwaters and is now confined to a few headwater streams. Abundances of Fusconaia masoni (Atlantic Pigtoe), Alismidonta undulata (Triangle Floater) and Strophitus undulatus (Squawfoot) may have been seriously reduced, but E. complanata appeared to have been unaffected (Clarke 1986).

Since C. fluminea's estimated filtering rates in freshwater tidal Potomac exceeded those for zooplankton by an order of magnitude (Cohen et al. 1984); food limitation of zooplankton (the cladocerans Bosmina sp.; Daphnia sp.; the copepod Eurytemora affinis; etc.) is possible, but has not been documented to our knowledge.

Habitat Change - Among changes possibly caused by C. fluminea's high filtering rates in the Potomac are included: increased light penetration; resulting in regrowth of native submerged aquatic vegetation,; decreased downbay transport of phosphates on particles; disappearance of blooms of the blue-green alga Microcystis between 1983 and 1993; and changes in sediment composition due to deposition of pseudofeces (Phelps 1994). Regrowth of native and introduced submerged aquatic vegetation in turn has positively affected waterfowl and fish populations (Killgore et al. 1989; Perry and Deller 1996; Phelps 1994). Additional factors, such as reduction of nutrient inputs are likely involved in these ecosystem-level changes, and the relative importance of the C. fluminea invasion remains to be determined.

Food/Prey - A wide variety of fishes are known to eat C. fluminea, but many of these species are not native to the Chesapeake region. Among possible native predators are suckers (Catostomidae); and White Catfish and Bullheads (Amieurus spp.) Fishes of the same families are listed by McMahon (1983) as predators of C. fluminea. Corbicula fluminea is an important food source for the endangered Shortnose Sturgeon Acipenser brevirostris and rare Atlantic Sturgeon A. oxyrynchus in the Delaware River (Horwitz 1986); and probably in the Chesapeake as well.

The crayfishes Cambarus bartoni (Appalchian Brook Crayfish, native) and Procambarus clarki (Red Swamp Crayfish, introduced) fed readily on C. fluminea 6-9 mm in size, but feeding rates were low relative to overall crayfish food intake and Corbicula biomass (Covich et al. 1981).

Five species of Chesapeake Bay ducks, Aix sponsa (Wood Duck), Anas clypeata (Northern Shoveler), Anas acuta (Pintail), Anas platyrhychos (Mallard), and Anas rubripes (American Black Duck) were found to be feeding on C. fluminea during 1973-76 (Perry 1981). Several additional species of diving ducks, known to feed on molluscs, Ring-Neck Duck (Athya collariformis), Bufflehead (Bucephala albeola), Canvasback (Athya vallisnerae), also increased in the freshwater tidal Potomac during the height of the Corbicula invasion (Phelps 1994).

Toxicity - While not inherently toxic, as very efficient filterers, C. fluminea accumulate toxicants in their tissue. C. fluminea could provide a new nutritious food source for waterfowl, but cause adverse effects on the birds by increasing body levels of toxicants (Perry 1981).

References - Clarke 1986; Cohen et al. 1984; Covich et al. 1981; Diaz 1994; Horwitz 1986; Killgore et al. 1989; Leff et al. 1990; McMahon 1983; Perry 1981; Perry and Deller 1996; Phelps 1994
Impacts on Non-natives:
Competition; Food/Prey; Habitat Change
As a rapidly reproducing and spreading filter-feeder, Corbicula fluminea (Asian Freshwater Clam) has probably had impacts on exotic as well as native biota within the tidal fresh region of estuaries. The most important of these may be promotion of exotic submersed aquatic vegetation, through increased water clarity due to filtration (Phelps 1994).

Competition - The estuarine ranges of C. fluminea and Rangia cuneata (Wedge Clam) overlap (Diaz 1974; Diaz 1994; Jordan and Sutton 1984; Posey et al. 1993), so that competion for food and space is possible, but we have not found documentation of this.

Food/Prey - Among introduced species known to eat C. fluminea (mostly juvenile clams) are Lepomis macrochirus (Bluegill), Lepomis microlophus (Redear Sunfish), Lepomis megalotis, Cyprinus carpio (Common Carp), Ictalurus punctatus (Channel Catfish), and Ictalurus furcatus (Blue Catfish) (McCrady 1990).

Habitat Change - Phelps (1994) argued that increased water clarity resulting from C. fluminea' s filtering facillitated the invasion of the Potomac River by Hydrilla verticillata in the 1980's (see 'Impacts on Residents'). Other introduced submerged aquatic vegetation, such as Myriophyllum spicatum (Eurasian Watermilfoil), Potamogeton crispus (Curly Pondweed), and Najas minor (Eurasian Water-Nymph), also would have benefited from these effects. Increased light penetration and vegetation growth, believed to be caused by C. fluminea's filtering (Phelps 1994), may have been responsible for increased fish populations (Killgore et al. 1989), including increased catches of Micropterus salmoides (Largemouth Bass) by sportsmen (Phelps 1994).

References - Diaz 1974; Diaz 1994; Jordan and Sutton 1984; Killgore et al. 1989; McCrady 1990; Phelps 1994; Posey et al. 1993


This data was last modified on Tuesday, September 13th, 2005.
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