Abstract

Freshwater mussels (family Unionidae) are long-lived filter-feeding bivalves that are important in maintaining ecosystem function by filtering particulate matter and sequestering nutrients in our waterways. Because they are exquisitely sensitive to environmental pollutants, they also serve as sentinels of environmental quality. Unfortunately, native freshwater mussels are the most imperiled group of animals in North America with more than 2/3 of nearly 300 identified species considered threatened, endangered, or extinct.³ Threats to these species include habitat degradation due to waterway manipulation, pollution, erosion and sedimentation, and invasive species. While translocation and captive propagation are widely supported as appropriate conservation measures, a high proportion of these unionids die within the first year of relocation, reducing the effectiveness of such efforts.² Furthermore, translocation of mussels presents a potential risk to other aquatic species in the event that these bioaccumulators can harbor pathogens and serve as vectors of disease. Historically, our ability to evaluate the health of freshwater mussels has been limited primarily to behavioral changes, mortality rates, and non-survival assays.

Our goal is to develop biomarkers of health, stress and disease in wild, captive and translocated freshwater mussels, in order to a) better manage them in captivity; b) assess the effects of environmental changes on in situ populations, and c) investigate their role as vectors and as sentinels of fish disease. Ongoing studies are evaluating changes in hematology, hemolymph chemistry, and catecholamine production in response to translocation.¹ New research is utilizing metabolic profiling to evaluate the effects of environmental changes, and the potential of freshwater mussels to harbor viral diseases of importance to fish.

Metabolic profiling studies are utilizing Amblema plicata, the three ridge mussel. A pilot study was designed to characterize the metabolic profile of mussels subjected to low nutrient availability. Eight mussels brought into captivity from the wild were isolated for 18 days without a food source. Hemolymph samples were taken prior to, and 9 and 18 days after the start of the study. Samples were analyzed on GC/MS and LC/MS/MS platforms, and 71 metabolites of known identity were detected. Captivity and fasting resulted in changes in energy metabolism, free amino acids, fatty acids, nucleic acids, and proliferation pathways. While fasting resulted in severe metabolite depletion, changes were also evident in many captive fed mussels, indicating that mussels may be experiencing nutritional deficiency and other metabolic stressors under common captive conditions.

Two species of mussels - the native Amblema plicata and the invasive Corbicula fluminea - were used in experiments to investigate mussels' ability to accumulate viral hemorrhagic septicemia virus (VHSv). VHS was recently introduced to the Great Lakes and poses a severe threat to the North American aquaculture industry. Each group of mussels was inoculated with 100 and 200 TCID₅₀ of VHSv, and issues were tested for the virus 72, 120, and 168 h post-inoculation using rt-PCR. Initial results indicate that freshwater mussels may harbor VHSV short-term, thereby serving as valuable indicators of the presence of the disease, but are unlikely to serve as vectors of VHSv.

Acknowledgments

The Morris Animal Foundation, the Ohio Division of Natural Resources, the Ohio State University Research Foundation, the Columbus Foundation and the Columbus Zoo and Aquarium are gratefully acknowledged for the support of this program.

*Presenting author

Literature Cited

1.  Burkhard MJ, Leavell SA, Weiss RB, Kuehnl K, Valentine KH, Watters GT, Wolfe BA. 2009. Analysis and cytologic characterization of hemocytes from freshwater mussels (Quadrula spp.). Vet Clin Pathol, 38(4):426–36.

2.  Cope WG, Hove MC, Waller DL, Hornback DJ, Bartsch MR, Cunningham LA, Dunn HL, Kapuscinski AR. 2003. Evaluation of relocation of unionid mussels to in situ refugia. J Molluscan Studies 69: 27–34.

3.  Williams JD, Waren ML, Cummings KS, Harris JL, Neves RJ. 1993. Conservation status of freshwater mussels of the United States and Canada. Fisheries 18(9): 6–22.