Figure 3

Low magnification view of coralline algae thallus with the selected area for Raman analysis marked (white square) (A; scale bar: 200 µm). Optical microscopy image of coralline algae cells with numbers 1 and 2 representing the punctual Raman analysis of the cell (B; scale bar: 20 µm) and their respective Raman spectra with a black arrow indicating the peaks that were used to differentiate high-Mg calcite (C; black arrow indicates the 281 cm⁻¹ calcite peak) from aragonite (2; black arrow indicates the 208 cm⁻¹ aragonite peak). Optical microscopy image overlaid by Raman mapping shows the prevalence of high-Mg calcite (green) in the internal cell wall and aragonite (red) as a “shell” in the inner part of the cell (D).