From morphology to nanoscale chemistry: resolving drivers of shell alteration in marine gastropods

The study investigated how coastal contamination and shell-boring organisms (bioerosion) jointly influence shell thickness and shape in the Mediterranean limpet Patella caerulea. By integrating morphometric, microstructural and high-resolution chemical analyses across contrasting environmental conditions, we studied the respective roles of these stressors on shell characteristics. Shell morphology varied markedly with infestation intensity, with highly infested limpets exhibiting flattened and thicker apex, reflecting a compensatory shell thickening of the apex observed through the deposition of additional aragonitic layers. In contrast, elemental composition was primarily associated with contamination, with significant differences in trace metal incorporation among populations. Microstructural analyses using Scanning Electron Microscopy (SEM) revealed a range of alterations results from both stressors, highlighting their combined influence at smaller structural scales. High resolution X-ray fluorescence mapping revealed significant variation in elemental composition among stations, providing new insights into the mechanisms of trace metal incorporations within the shell matrix. Overall, this study demonstrates that both boring organisms (bioerosion) and coastal contamination affect distinct yet complementary aspects of shell characteristics, emphasizing the need to consider multiple levels of spatial resolution when using shell characteristics as environmental indicators.