Feeding ecology of three freshwater mussel species (Family: Unionidae) in a North American lentic system

Freshwater mussels are typically considered to be primarily filter-feeders with an ability to pedal feed, however there is limited information regarding interspecific differences in food resources and feeding modes. The objective of this study was to investigate interspecific variation in food resource usage among mussels in a lentic system associated with a reservoir drawdown. We quantified carbon-13 and nitrogen-15 isotopic signatures for three mussel species, including a Federally Threatened species, and their potential food resources in Gantt Lake, Alabama, USA. For all species, carbon-13 derived from limnetic, benthic fine particulate organic matter (FPOM) contributed on average 99% to the mussel diet. Paradoxically, mussels collected from the littoral zone relied primarily on food resources from the limnetic zone, although this spatial disconnect may have been an artifact of the sampling regime. Carbon-13 associated with littoral FPOM, limnetic and littoral suspended particulate organic matter (SPOM) and coarse particulate organic matter (CPOM) contributed < 1%. Elliptio pullata (Lea, Proceedings of the Academy of Natural Science 8: 262, 1856) collected live but emersed for 8 weeks were enriched in nitrogen-15, providing evidence of catabolism during emersion. Results suggest that benthic sources can be a dominant food resource for unionids and that stranded unionids rely on internal energy stores to survive emersion.