Microstructural shell strength of the Subantarctic pteropod Limacina helicina antarctica

Anthropogenic inputs of CO₂ are changing ocean chemistry and will likely affect calcifying marine organisms, particularly aragonite producers such as pteropods. This work seeks to set a benchmark analysis of pteropod shell properties and variability using nanoindentation and electron microscopy to measure the structural and mechanical properties of Subantarctic pteropod shells (Limacina helicina antarctica) collected in 1998 and 2007. The 1998 shells were collected by a sediment trap deployed at 2000 m, 47°S, 142°E, and the 2007 shells were collected using nets from mixed-layer waters in the region (44°–54°S, 140°–155°E). Transmission electron microscopy revealed that the shells are composed of a polycrystalline structure, and no obvious porosity was visible. The hardness and modulus of the shells were measured using shell cross-section nanoindentation, across various regions of the shell from the inner to outer whorl. No change in mechanical properties was found with respect to the region of the shell cross-section probed. There was no statistically significant difference in the mean modulus or hardness of the shells between the 1998 and 2007 data sets. No major changes in the mechanical properties of these pteropod shells were detected between the 1998 and 2007 data sets, and we discuss the possible biases in the sampling techniques in complicating our analysis. However, quantifying the mechanical properties and microstructure of calcified may still provide insights into the responses of calcification to environmental changes, such as ocean acidification.