Meeting Abstract
The Atlantic ghost crab is found on sandy beaches, which are naturally-complex environments. Not only will sand shift and flow in response to the intrusion of leg, fragments of shells and rocks can perturb their locomotion. The goal of this study was to establish how ghost crabs respond to sudden changes in substrate properties. Crabs were exposed to three treatments: control (all sand), a low-traction hard surface, and a high-traction hard surface. Because crabs were running on a sand trackway, perturbations introduced changes to both surface friction and yield. Twenty crabs were filmed with a high-speed camera (500 fps) capturing dorsal and two lateral views. Kinematics were compared among strides before, during, and after the perturbation. We hypothesized that the perturbations would decrease locomotor performance among ghost crabs, and that slip perturbations have a greater impact on locomotor performance compared to non-slip perturbations. Contrary to expectations, results show that the perturbations had no impact on locomotor kinematics while in contact with either surface, regardless of traction (P > 0.05: running speed, body height, stride frequency, duty factor, body pitch and roll), despite all individuals slipping on the low-traction surface. However, the subsequent step back onto sand showed decreases in running speed and body height (P < 0.05: mixed model ANCOVA), potentially due to limb penetration into the surface. These results suggest that momentum allows ghost crabs to maintain stable locomotor dynamics when encountering hard surface perturbations of varying frictions for at least the initial perturbed footfall. Future studies with more sustained perturbation are necessary to determine if other corrective measures are necessary to allow continued stable locomotion following a surface transition.
