TAPHONOMIC PATTERNS AND PREDATION TRACES RECORDED IN LIVE, DEAD, AND FOSSIL MOLLUSCAN ASSEMBLAGES OF FLORIDA SPRINGS AND RIVERS

In recent years there have been increased threats to freshwater species from climate change, human activity, invasive species, rising sea levels, and habitat destruction. Taphonomic attributes of molluscan assemblages can offer historical insights into ecological, environmental, and biological changes in freshwater ecosystems. In this study we taphonomically scored and identified predation traces in three assemblage types: live (living specimens), dead (loosely accumulated shells) and fossil (collected in situ from late Pleistocene-Holocene sediments) gastropods from the Wakulla, Silver, and Ocklawaha Rivers in Florida. We scored 5226 specimens of four freshwater species: Pomacea paludosa (n=456), Callinina georgiana (n=1450), Planorbella trivolvis (n=642), and Planorbella duryi (n=2679) from all three assemblage types. Each specimen was scored on aperture damage, body damage, color, abrasion, spire condition, and exterior texture. Additionally, the presence of predation traces such as repair scars, holes, or scrapes was noted. Individual trait values were combined into a z-standardized Total Taphonomic Score (TTS) representing a degree of alteration to each specimen. A more negative TTS represented a less altered specimen while a more positive TTS was indicative of significant shell deterioration.

Fossil specimens exhibited, on average, the highest TTS (0.29), reflecting greatest alteration. Live specimens were least altered (-7.91), while death assemblage specimens were highly altered (0.09), only slightly less than fossil specimens. This agrees with previous research that freshwater death assemblages may be formed by both reworked fossil material and recently dead individuals. Trends are similar across species and river systems, suggesting similar taphonomic pathways. Live specimens exhibited the highest rates of predation (56%) compared to death (25%) and fossil (27%) specimens, potentially reflecting a recent increase in predation related to rising sea levels or introduced species. The tidally influenced Wakulla River exhibits the highest predation rates of the studied rivers. Live, death, and fossil assemblages record a history of change to freshwater springs and rivers, but these results suggest that complex taphonomic pathways control fluvial assemblage formation.