HIGH-RESOLUTION GEORADAR IMAGING OF SIMULATED AND POST-EMERGENCE SEA TURTLE NESTS: IMPLICATIONS FOR PALEOICHNOLOGY AND CONSERVATION

This study presents one of the first ground-penetrating radar (GPR) databases of post-emergence sea turtle nests, ichnologically understudied and relatively complex biogenic structures. A simulated structure (Deuaville Beach, DE) and two in situ post-emergence sea turtle nests (Sandbridge Beach, VA) were imaged with an 800 MHz setup, complemented with sediment texture and magnetic susceptibility analyses. The simulated field experiment closely followed an ethological sequence on an aeolian ramp (foredune base), with three sets of grid surveys: pre-excavation (background), following “oviposition” (active nest), and post-emergence (final biogenic structure). The egg clutch was mimicked by ~50 limes buried at 0.5-1.0 m. Ten shore-parallel (5 background, 4 over the “active” nest, 1 post-emergence) and two short-normal transects (1 each pre- and post-emergence) were collected at a 0.9 m spacing, followed by time-triggered images that simulated hatchling emergence. Subsurface deformation was characterized by a substantial increase in GPR image complexity. At Sandbridge, GPS coordinates were used as approximate guides to the locations of a recent (August 2021) Kemp’s-Ridley (Lepidochelys kempii) and an older (August 2020) Loggerhead (Caretta caretta) nests. At the 2021 site, a clear anomaly was identified, including a V-shaped truncation (width: 0.4-0.5 m; depth: ~0.8 m). At that depth, subsurface breaks in a marker layer of heavy minerals support the geophysical data. At the 2020 site, GPR served as the primary method for locating a shallow subsurface anomaly similar to the L. kempii nest. All three imaged structures were within dry to slightly saturated (<10% moisture) medium sand. Numerous ghost crab burrows, some imaged as part of surveys, place sea turtle nests into the Psilonichnus ichnofacies, with overprinting representing a contemporary ichnocoenosis rather than a facies shift. Our findings serve as a proof of concept for small-scale laboratory experiments of biogenic deformation using a 2300 MHz antenna over dry to fully saturated sand. This research has wide-ranging implications for conservation of endangered species, with additional potential for nest recognition in ancient sequences and for distinguishing them from morphologically similar physical structures (shallow paleo-channels).