Characterization of Post-mortem Shell Alteration in Aransas Bay, Texas
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Accumulations of dead shells in both modern coastal settings and in the rock record contain valuable information on past ecosystems and environmental conditions. However, death assemblages are not simply snapshots of living communities; rather, the abundances of different species have been biased due to differential rates of postmortem destruction. In order to constrain the nature and degree of bias in modern molluscan death assemblages in a shallow marine environment, I deployed mesh-bag experiments including six species of bivalves into a natural marine environment on the Texas coast. The mesh bag design for tethering shells allowed for maximum exchange between ambient environmental conditions and the shells while the apparatus was deployed. The apparatuses were recovered after 2 weeks, 4 weeks, 8 weeks, 16 weeks, 8 months, and 12 months. Shells were examined under a Scanning Electron Microscope (SEM) to analyze integrity, document degradation, and investigate patterns of biological, chemical, and physical abrasion and destruction. SEM analysis indicates that some shells clearly degraded, while others did not, even after 12 months. In addition, epifaunal shells experienced postmortem encrustation by sessile organisms more than infaunal shells, indicating a species-level preservational bias.
Schirm, David Edward (2013). Characterization of Post-mortem Shell Alteration in Aransas Bay, Texas. Master's thesis, Texas A & M University. Available electronically from