PT19 Unique Demands of Endangered Species Evaluations
Exhibit Hall
8:00 AM - Tuesday
(PT281) Use of Relic Unionid Shells to Determine Time since Mortality.
Ashcraft, E1, Farris, J1, 2, Hannigan, R2, 1 Arkansas State University Department of Biological Sciences, State University, AR, USA2 Arkansas State University Environmental Sciences Program, State University, AR, USA
ABSTRACT- Freshwater mussel shells are composed of a calcium carbonate matrix which remains in the environment for a substantially longer time than the living mussel itself. Relic shells contain valuable information pertaining to mussel life history, mortality, and taphonomy. Because mussel mortality may be indicative of ecosystem impairment and/or degradation, the ability to identify time passed since mortality occurred to a mussel provides evidence in determinations of causality, responsibility, and reciprocity. Such information may be gained through the analysis of relic shells. Using freshwater mussels within the family Unionidae and freshwater bivalve surrogates (i.e. Corbicula fluminea), identification and measurement of factors influencing decomposition rate for the visceral mass, periostracum, nacre, hinge and overall valve condition are being made through both laboratory and field experimentations. Use of X-Ray diffraction of internal shell structure, or nacre, indicates any calcium carbonate form variations within and among shells of different age and species. Digital microscopy imaging with polarized light and geographic information system (GIS) mapping of shell thin-sections allow analysis of shell cross sections through comparisons of percentages of aragonite, calcite, and other forms of calcium carbonate. Analysis with polarized light may also indicate any mineral replacements within the shell structure as well. Validation of these methods through field deployments is currently underway. Through the selection of factors that influence decomposition and decomposition rate, a metric that incorporates measurable changes in shell integrity may be determined for the amount of time since mortality for a specific shell. The consideration for these rates will incorporate both site and species-specific factors, and is being developed and tested on relic shells whose time since mortality can be validated.
Key words: relic shells, decomposition rate, Unionidae, taphonomy