Amphistegina lessonii and Amphistegina lobifera shell microstructure, texture and twinning pattern reflect resilience to cadmium and lead

Biologically secreted carbonates are archives of environmental conditions, as shell and skeletal element minerals record chemical and physical signals of the ambient environment. We report the impact of Cd²⁺ and Pb²⁺ on foraminiferal shell crystal structural and organizational characteristics, such as microstructure, texture, crystal co-orientation strength and crystal twin formation for the rotaliid foraminifera Amphistegina lessonii and Amphistegina lobifera. The investigated species lived first in Cd²⁺- and Pb²⁺-free and, at a later growth stage, in Cd²⁺- and Pb²⁺-containing water. Enrichment in Cd²⁺ was increased 4 times relative to the ecological criteria maximum concentration (CMC) for both species. For Pb²⁺, it was increased 5 times for A. lobifera and 6 times for A. lessonii. Crystal organization was measured with Electron-Backscattered-Diffraction (EBSD), shell structure was imaged with FE-SEM. We detect that the Cd²⁺ and Pb²⁺ concentrations influence the degree of shell calcite twin formation. For A. lessonii the addition of Cd²⁺ to the water prevents crystal twin generation, Pb²⁺ induces decreased twinned calcite secretion. For A. lobifera, both Cd²⁺ and Pb²⁺ significantly decrease crystal twin formation. Our study indicates that crystal twin generation by Rotaliida can be developed as a structural indicator for environmental pollution with heavy toxic elements.