Meeting Abstract

P1-61   -   Compressive Characteristics of juvenile green turtle (Chelonia mydas) shells Serra, I/J*; Wyneken, J; Department of Biological Sciences, Florida Atlantic University, Boca Raton, FL; Department of Biological Sciences, Florida Atlantic University, Boca Raton, FL ilezcano2018@fau.edu http://biology.fau.edu/marine-lab/people/ivanaserra.php

The hard, boney shells of turtles act as the organism’s first line of defense against a variety of natural and, increasingly, anthropogenic threats. The shell has long been perceived as a form of armor because it consists of strong bone encasing the spinal cord, limb girdles, and viscera. The carapace arises from the expansion of ossified ribs and neural arches joined via collagenous sutures. Keratinous scutes cover the bony elements. Though this multi-layered structure seemingly serves a protective role, the mechanical properties of shells only recently were measured, and then in just a few turtle species. The majority of this work focuses on semiterrestrial (Terrapene carolina) and freshwater (e.g. Chrysemys picta, Trachemys scripta, Malaclemys terrapin) emydid species. The shells of marine turtles, species that spend virtually their entire lives at sea, have not been tested although their shells and lifestyles differ greatly from those of emydids. We investigated the mechanical properties of fresh juvenile green sea turtle (Chelonia mydas) shells obtained through rehabilitation facilities and fresh strandings in Florida. Whole bone and suture samples were excised from shells and tested under quasi-static compression. Resulting force-deformation curves were converted to stress-strain curves in order to quantify the Young’s modulus and energy absorption of individual samples. Our data suggests that sea turtle shells are much less stiff, with lower Young’s moduli, than their freshwater and semiterrestrial counterparts. Marine turtle shells have the capacity to deform substantially under relatively low stresses. This trait potentially aids marine turtles that experience oscillations from low to high pressures as they dive and surface to breathe. Additionally, our results indicate that stiffness may vary by region with average stiffness slightly decreasing in the antero-posterior axis.