INFLUENCE OF IONIC STRENGTH ON THE PRESERVATION POTENTIAL OF THE BLACK-BACKED LAND CRAB, GECARCINUS LATERALIS, SAN SALVADOR, BAHAMAS

Most taphonomic pathways for soft-tissue preservation require minerals either forming on the surface of or replacing tissues. Among various other factors, the rates at which these reactions occur impact the quality of fossil preservation. Comparatively, rapid mineral precipitation has the potential to retain finer morphological features, whereas slower reactions allow for significant information loss through decay. In marine settings, such reaction rates are affected by the high abundance of dissolved ions (ionic strength). The goal of this study was to determine how differing ionic strengths, in turn, affect early taphonomic processes using field-based, actualistic decay experiments. The experiments were conducted with freshly euthanized Gecarcinus lateralis, emplaced in three natural settings of varied salinities on San Salvador Island, Bahamas (from high to low): Storr’s Lake, northern Pigeon Creek, and Blue Hole, with a normal marine salinity control group in the wet lab at the Gerace Research Centre. Over the course of 25 days, samples were removed from the sites, photographed, and ranked on several decay features: color loss, water retention in limbs and membranes, disarticulation, fragmentation, soft tissue loss, and cuticle flexibility. Sediment and carapace samples were taken and later analyzed for mineral precipitates with SEM. Water samples from each locality were analyzed to determine their ionic strength, and salinities were monitored in the field. A decay index was created by converting all decay character scores to z scores and summing the values for each observation. Linear models predicting the decay index were compared by small-sample corrected Akaike information criterion (AICc). The model with the lowest AICc had 4 predictors: site, days decaying, burial depth, and carapace width. Pairwise comparisons of the sites indicated significant differences between the control site and Pigeon Creek, and Storr’s Lake and Pigeon Creek samples. The chemical compositions of the sediment samples were analyzed using ordinations and linear models to assess the importance of ionic strength in predicting the presence of taphonomically relevant minerals.