abstract
The Asian clam, Corbicula fluminae, is native to many parts of Africa, Asia, and Australia.1,2 It was first introduced to the United States in 1938 (Columbia River, Washington)3 and over the subsequent decades has become established in 38 states and the District of Columbia.2 This invasive species has been highly successful, and may have a negative impact on native bivalve species.4,5,6,7 While challenging to prove, large numbers of Corbicula can compete with native bivalves for resources,7 consume gametes and larvae of native species, and locally pollute the aquatic environment following large die-offs.4,6 Biofouling of industrial water supply systems and power plants represents the Asian clam's biggest negative economic impact.2,8,9
A number of studies have examined bivalve mollusks as bioindicators for heavy metal pollution.10-12 The goal of the present study was to compare a panel of metal concentrations between hard and soft tissue samples from Asian clams and between Asian clam samples from a Florida and North Carolina watershed. The importance of freshwater bivalve mollusks as bioindicators of ecosystem health will be reviewed and emphasized during the presentation.
Mature C. fluminae, ranging from 2.38 g to 14.31 g, were obtained from four localities (two in Florida and two in North Carolina). Once the animals were weighed and measured, the valves were gently separated with a scalpel blade, and secured with a wooden applicator stick. Animals were euthanized with a 400 mg/L tricaine methanesulfonate (MS-222) 15-60 minute immersion. A clean scalpel blade was used to remove the soft tissues from the shell and the specimens were placed in sterile Whirlpacs®, refrigerated at 4°C, and subsequently shipped to the Washington Animal Disease Diagnostic Laboratory, College of Veterinary Medicine (Washington State University, Pullman, WA. 99164-7034). Sample analysis was conducted using inductively coupled plasma (ICP) at the Analytical Sciences Laboratory, University of Idaho (Holm Research, Moscow, ID 83844-2203). At least one animal from each study site was preserved in 10% neutral buffered formalin for histopathological analysis (results pending).
Soft tissue and shell samples were analyzed for: Arsenic (As), cadmium (Cd), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), lead (Pb), and zinc (Zn). Data analysis indicates that concentrations of Fe, Mn, and Mo were generally higher in soft tissues while Cd, Cu, Pb, and Zn levels were greater in the shells. Preliminary evaluation of the data shows that metal concentrations were similar when comparing samples from the different sites.
It is hoped that this pilot study will provide baseline data for future work examining heavy metal concentrations in North American bivalve mollusks.
acknowledgements
We thank Diane Deresienski, Brian Rolek, Geoffrey Hill, Craig Harms, Jay Levine and the NCSU-CVM Aquatic Epidemiology and Conservation Laboratory, and the NCSU-CVM Department of Clinical Sciences for assistance and support.
References
1. Morton, B. 1986. Corbicula in Asia--an updated synthesis. American Malacological Bulletin, Special Edition No. 2:113-124.
2. www.usgs.org (accessed Feb. 24, 2008).
3. Counts, C. L., III. 1986. The zoogeography and history of the invasion of the United States by Corbicula fluminea (Bivalvia: Corbiculidae). American Malacological Bulletin, Special Edition No. 2:7-39.
4. Yeager M.M., Neves R.J. and Cherry D.S., 2000. Competitive interactions between early life stages of Villosa iris (Bivalvia: Unionidae) and adult Asian clams (Corbicula fluminae). In: Johnson P.D. and Butler R.S., eds. Freshwater Mollusk Symposium Proceedings, Part II: Proceedings of the First Symposium of the Freshwater Mollusk Conservation Society, March 1999, Chattanooga, TN. Ohio Biological Survey, Columbus, OH. Pp. 253-259.
5. Leff L.G., Burch J.L. and McArthur J.V., 1990. Spatial distribution, seston removal, and potential competitive interactions of the bivalves Corbicula fluminae and Elliptio complanata, in a coastal plain stream. Freshwater Biology, 24:409-416.
6. Strayer DL. 1999. Effects of alien species on freshwater mollusks in North America. Journal of the North American Benthological Society, 18(1):74-98.
7. Neves RJ, Widlak JC. 1987. Habitat ecology of juvenile freshwater mussels (Bivalvia: Unionidae) in a headwater stream in Virginia. American Malacological Union Bulletin, 5(1):1-7.
8. Isom BG. 1986. Historical review of Asiatic clam (Corbicula) invasion and biofouling of waters and industries in the Americas. American Malacological Bulletin, Special Edition No. 2:1-5.
9. Williams CJ, RF McMahon. 1986. Power station entrainment of Corbicula fluminea (Müller) in relation to population dynamics, reproductive cycle and biotic and abiotic variables. American Malacological Bulletin, Special Edition 2:99-111.
10. Cataldo DH, Boltovskoy D, Stripeikis J, Pose M. 2001. Condition index and growth rates of field caged Corbicula fluminea (Bivalvia) as biomarkers of pollution gradients in the Parana River Delta (Argentina). Aquatic Ecosystem Health and Management, 4:187-201.
11. Ravera O, Beone GM, Cenci R, Lodgiani P. 2003. Metal concentrations in Unio pictorum mancus (Mollusca, Lamellibranchia) from 12 northern Italian lakes in relation to their trophic level. Journal of Limnology, 62(2):121-138.
12. Li Y, Yu Z, Song X, Mu Q. 2006. Trace metal concentrations in suspended particles, sediments and clams (Ruditapes philippinarum) from Jiaozhou Bay of China. Environmental Monitoring and Assessment, 121:491-501.