Coral Extension Rate Analysis Using Computed Axial Tomography

Abstract

Biological and geological studies of coral reefs often rely on measured Scleractinian coral skeletal extension rates. Ideally, corallites are oriented parallel to a coral core’s longitudinal axis and perpendicular to its annual high-density growth bands. To examine corallite orientations, we use high-resolution computed axial tomography to image ten short Montastrea faveolata cores from the northwest Gulf of Mexico. This non-destructive method enable the comparison of extension rates determined several ways: 1) across a single slice or slab X-ray image, 2) between 0.6 mm slice and 8.4mm slab X-ray images, and 3) among slice/slab orientated at varied angles relative to a coral core’s longitudinal axis. Additionally, the true three-dimensional extension rate of individual corallites is determined and compared to the extension rate apparent on a twodimensional slice/slab. Results suggest minimal significant differences between all methods, confirming the conventional extension rate methodology is suitable for studies if the core’s longitudinal axis is in approximate alignment with the growth axis of the corallites. Determination of three-dimensional corallite growth patterns leads to improved understanding of the development of the coral colony.