Invasion of the Southeastern United States: Using Oxygen Isotope Sclerochronology to Determine Temperature Tolerances of Pomacea maculata

Session: Timestamped Biomineralized Structures in Coastal Environmental Monitoring and Cultural Research

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Abstract:

The sequential and predictable shell growth of aquatic gastropods allows for organismal life history reconstruction using stable oxygen isotope sclerochronology. We apply this approach to estimate thermal limits and potential range expansion of Pomacea maculata, a globally invasive freshwater snail that threatens native biodiversity, agriculture, and human health. As a stenothermal tropical species, P. maculata is primarily restricted by cold temperature tolerance. Consequently, current biogeographic range models rely on thermal thresholds established by controlled cold-stress exposure experiments. However, the accuracy of temperature thresholds derived in laboratory settings is limited by our ability to replicate natural environmental conditions and account for local adaptations and organismal survival mechanisms. Analyzing the oxygen isotope composition (δ¹⁸O) of P. maculata at the edge of their invasive range offers an alternative means of estimating cold tolerance; this method circumvents the limitations of laboratory-based approaches by capturing conditions experienced by wild populations.

In this study, we examined P. maculata specimens from two localities near the Mobile-Tensaw Delta in coastal Alabama. For approximately one year prior to collection, we logged water temperature hourly and monitored water δ¹⁸O weekly. We performed sequential micromilling along the shell whorl of each specimen to obtain powdered aragonite for δ¹⁸O analysis. Shell regions showing visibly abnormal growth consistent with cold stress were identified and milled at higher resolution to capture near-daily conditions. Using the annual water δ¹⁸O and temperature data, we built an idealized time-series model of shell δ¹⁸O assuming conditions of continuous growth. Discrepancies between the idealized model and the measured shell δ¹⁸O values allow us to identify the temperatures at which P. maculata undergoes cold stress approaching mortality. Our preliminary data suggest that this species is experiencing and recovering from temperatures lower than previously established physiological thresholds.