LIVE-DEAD FIDELITY OF MULTI-TAXIC ASSEMBLAGES: RELATIVE TAPHONOMIC BIASES ACROSS MAJOR GROUPS OF MARINE BENTHOS (NORTH CAROLINA, USA)

Although paleontological studies commonly examine multiple higher taxa simultaneously, quantitative analyses comparing living communities with sympatric death assemblages are typically restricted to a single taxon, primarily more heavily calcified organisms such as mollusks. Few studies include multiple phyla and consequently our understanding of whole assemblage fidelity and relative taphonomic biases across higher taxa remain limited.

To quantitatively assess taphonomic biases across multiple invertebrate groups with variable biomineralization (bivalves, gastropods, echinoids, decapods, and chelicerates), we have targeted the subtidal benthos of coastal North Carolina. Initial results include sites variably affected by anthropogenic changes, ranging from moderately to severely impacted localities (May 2011, Beaufort, NC). Species-level estimates of diversity and relative abundance for living populations and death assemblages were obtained for 5 sites (by dredging) for multiple higher taxa. Relative fossilization potential was estimated for each major group and live-dead fidelity was assessed using the Jaccard-Chao Spearman-Rho fidelity plots of Kidwell (2007).

These initial results indicate the presence of strong relative biases: death assemblages are overwhelmingly dominated by mollusks, whereas living communities also include notable quantities of arthropods and echinoderms. When all higher taxa are included, all 5 dredge samples show low live-dead fidelity (low Jaccard-Chao Spearman Rho coefficients), although the “moderately-impacted” samples show better fidelity than the “severely-impacted” ones. When the fidelity analysis is repeated for mollusks only, the coefficients improve notably for moderately-impacted sites.

Understanding relative higher-taxon fidelity is critical for studying large-scale patterns in the fossil record, where multiple major taxonomic groups are analyzed or assessed jointly. Our pilot results suggest that strong taphonomic filters can alter relative abundance of higher taxa. In addition, while mollusk-based fidelity analysis provides a powerful tool for assessing anthropogenic changes, other groups, with lower fossilization potential, may be less informative or more difficult to interpret in terms of human impacts on ecosystems.