Fig. 4.

Comparison of [Ca] maps, component maps, and PIC maps of the same area at the growth surfaces of fresh, forming skeletons of M. lordhowensis (Ml) (A–C) and Acropora sp. (As) (D–F). (A) Notice the 7- to 8-µm-thick low-[Ca] band at the forming surface in a (left edge). As indicated by the grayscale bar, brightness is proportional to [Ca], but is not calibrated. Resin with no Ca is black, crystalline aragonite is bright gray in mature skeleton (right side). (D) [Ca] map showing the 15-µm-wide microporous band at the forming surface (left). In D the [Ca] is identical in the microporous and the space-filled regions (left and right, respectively), indicating that each particle on the left is fully dense, but particles do not fill space, they are interspersed with the embedding resin. (B and E) Component maps showing a few amorphous pixels at the growing surfaces. The low-[Ca] band in a is mostly crystalline aragonite (blue pixels) in the component map in B. Also, in E, most pixels are evenly crystalline aragonite (blue), in both the microporous layer and the bulk mature skeleton. (C and F) PIC map, where the orientation of the aragonite crystal in each 60-nm pixel is measured and quantitatively displayed in color, including hue and brightness, corresponding to in-plane and off-plane angles in polar coordinates.