Abstract

Bivalves are often used as sentinels for marine and freshwater ecosystems alike. Subject to land use changes, water quality degradation and other environmental pressures, many once thriving bivalve populations are in decline. Although there are many potential causes for the declines, the methods available for health evaluation are limited due to the sensitivity of our diagnostics and our understanding of bivalve physiologic response to stressors. The same is true for many aquatic species.

From 2004–2009, dramatic declines in the Appalachian Elktoe (Alasmidonta raveneliana) population of the Little Tennessee River in North Carolina were punctuated by two acute die-off events. Surviving mussels appear to be in suboptimal health, showing decreased growth rates. Since the first die-off in 2004, efforts have been made to understand why only this one species in the river have been affected, and why populations in a sister river, the Tuckasegee, remain apparently unaffected. Water quality data have been sparse and unhelpful. Traditional diagnostics such as histopathology and bacterial culture have yielded no potential cause of death. Nutritional analysis showed an apparent elevation of manganese in the tissue and shell of Alasmidonta individuals, most pronounced in samples from the Little Tennessee. This suggests a possible species difference in manganese metabolism.

Unfortunately, little is known about freshwater bivalve metabolism on any level.

We discuss the use of nuclear magnetic resonance (NMR) as a diagnostic technique for the investigation of disease at a metabolic level in freshwater bivalves. One of several techniques used in the field of metabolomics (sometimes called metabonomics), NMR allows detection of tens to thousands of metabolites within the cells, tissues or biofluids of an organism. The data yielded in a single metabolomic profile, or metabolome, yield a robust image of health status, in contrast to the relatively small picture we obtain when measuring even a standard biochemical profile.

By applying these techniques to the effort to understand and diagnose a bivalve die-off in the Little Tennessee River, we can describe the major endogenous metabolites in Alasmidonta raveneliana, use statistical methods to show metabolic differences between experimental groups, and highlight possible metabolic pathways affected by the disease process.

Acknowledgements

The authors would like to acknowledge all the participants in the overarching investigation from NCSU, NCWRC, USFWS, NCEEP, USGS and beyond. And thank you to the University of North Carolina, Department of Biomedical Engineering for aid in development of the NMR techniques.