Deciphering mollusc body shape adaptations to varying hydrodynamic conditions and substrate types

Shell morphology in intertidal gastropods reflects environmental conditions, especially hydrodynamic forces and substrate characteristics. We investigated shell shape variation in the commercially exploited grazer Phorcus sauciatus across contrasting coastal orientations, North versus East, and substrate types, natural versus artificial, in Gran Canaria. A total of 378 specimens were collected from exposed and sheltered environments, including rocky platforms, large rocks, and artificial structures such as breakwaters and seawalls. Geometric morphometrics, using anatomical landmarks and outline curves, together with size-standardised shell measurements, showed that coastal orientation was the main driver of morphological variation. Northern groups had lower, more horizontally elongated shells consistent with high wave exposure, whereas eastern groups showed taller, more globose shells associated with sheltered conditions. Substrate type modulated local-scale shape differences. Platform-associated groups showed the highest morphological disparity, suggesting greater within-group morphological dispersion, while artificial substrates and rock habitats showed lower variability and more restricted morphospace occupancy. Discriminant and canonical variate analyses provided moderate cross-validated classification accuracy, indicating partial separation and substantial overlap among groups. These results show that shell morphometrics can detect environmentally associated shape variation and provide a complementary tool for spatial monitoring and management of data-limited intertidal fisheries.