Kaelyn Fogelman1, Jim Stoeckel1, Brian Helms2 ... Additionally, we would like to thank Brad Littrell, Kyle Sullivan and Ed Oborney at BIO-. WEST, Inc., Tim ...
Food web ecology of freshwater mussels (Family: Unionidae) in central Texas Kaelyn
1 Fogelman ,
Jim
1 Stoeckel ,
Brian
2 Helms
Auburn University, School of Fisheries, Aquaculture and Aquatic Sciences, Alabama1 2 Troy University, Department of Biological and Environmental Sciences, Alabama
Introduction Three species of Texas-endemic unionid mussels (Cyclonaias houstonensis, Cyclonaias petrina and Lampsilis bracteata; Figure 1) are current candidates for federal listing under the Endangered Species Act. Although it is widely accepted that freshwater mussels are filterfeeders, much remains unknown regarding their dietary preferences and requirements1. It is necessary to understand the diet of these organisms to properly assess their imperilment and to effectively inform conservation and management practices. Stable isotope analysis is an effective way to estimate consumer feeding patterns through the identification of primary carbon sources and trophic position2,3,4.
Results Mussels sampled were consistently nitrogen-enriched across seasons and basins (Figure 3).
Suspended particulate organic matter and benthic sediment contributed only a minor amount of dietary carbon in most cases.
Mussel stable isotope signatures have minimal variability across seasons (Figure 3).
Data suggest that the focal mussels primarily utilize pedal feeding to access benthic detritus and/or associated bacteria and fungi rather than filter feeding to access suspended food resources such as phytoplankton.
When more than one focal taxa are present in a basin, both species appear to feed similarly within basins based upon preliminary analyses (Figure 3). CPOM was identified as a primary source of dietary carbon for all focal taxa across all seasons analyzed, with the exception of L. bracteata in the middle Colorado in Spring 2017 (Figure 4).
Ongoing Work
Objectives
IsoSource mixing models will determine relative contribution of each food source sampled in October 2017.
1.Identify potential food resources utilized for focal taxa in four basins. 2.Determine if there is spatial or temporal variability in feeding within and among species.
Field samples were collected seasonally in the upper Guadalupe, lower and middle Colorado and lower Brazos river basins in 2017 (Figure 2). Mussel foot tissue was sampled and each species was sampled in two separate basins. Potential food resources sampled included: suspended particulate organic matter (SPOM), fine particulate organic matter associated with benthic sediments (FPOM), coarse particulate organic matter (CPOM) and vegetation. Samples were analyzed for d13C and d15N at Washington State University Stable Isotope Core Laboratory using GC/MS. Contribution of various potential food items was determined with IsoSource mixing models5. Figure 2. Map of Texas river basins with study sites denoted.
It has yet to be determined whether the carbon that is assimilated from CPOM is from the litter itself, or the microbial biofilm associated with it. Nitrogen fractionation (Figure 3) suggests that there may be one or more food resources that our data has not captured.
Figure 5. Example of habitats in which unionid mussels may be found, including organic rich substrates (left) and substrates dominated by inorganics (right).
Figure 1. Texas-endemic mussels targeted in this study: Cyclonaias petrina (left), Cyclonaias houstonensis (center) and Lampsilis bracteata (right).
Materials and Methods
Discussion and Conclusions
Figure 3. Example of stable CN isotope biplots. Data is from unionid and food resource samples collected from the upper Guadalupe River in April (Spring) and July (Summer) 2017.
Sampling was conducted in May 2018, with the objective of isolating and analyzing benthic microbial biofilms. GC/MS analysis will be completed and the signatures will potentially elucidate the food sources that have yet to be captured. To further analyze existing trends in unionid feeding ecology, a meta-analysis is being conducted on existing literature with basal food web stable isotope data.
Acknowledgements We would like to acknowledge the Texas Comptroller of Public Accounts and Texas State University for funding. Additionally, we would like to thank Brad Littrell, Kyle Sullivan and Ed Oborney at BIOWEST, Inc., Tim Bonner at Texas State University and Rebecca Tucker and Austin Haney at Auburn University for field assistance.
Figure 4. Estimated carbon source of C. houstonensis, C. petrina and L. bracteata in the upper Guadalupe, lower and middle Colorado, and lower Brazos river basins. Chart reflects mean estimate values of potential carbon sources calculated using IsoSource mixing models.
References 1. Strayer, DL. 2008. Freshwater Mussel Ecology. Berkeley, CA: University of California Press. 2. Cabana, G, and JB Rasmussen. 1996. Comparison of aquatic food chains using nitrogen isotopes. Proceedings of the National Academy of Science. 93: 10844-10847. 3. Vuorio, K, M Tarvainen, and J Sarvala. 2008. Unionid mussels as stable isotope baseline indicators for long-lived secondary consumers in pelagic food web comparisons. Fundamental and Applied Limnology. 169(3): 237-245. 4. Newton, TJ, CC Vaughn, DE Spooner, J Nichols, and MT Arts. 2013. Profiles of Biochemical Tracers in Unionid Mussels Across a Broad Geographical Range. Journal of Shellfish Research. 32(2): 497-507. 5. Phillips, DL, SD Newsome, and JW Gregg. 2005. Combining sources in stable isotope mixing models: alternative methods. Oecologia. 144: 530-547.
