A Windows-based Program for Image Processing Coral Skeletal Densitometry

Coral skeletal density information is a useful growth parameter and may be coupled with extension rates to determine calcification rates. The conventional process for density determination is often cumbersome and requires some parameters which are difficult to precisely specify (e.g., Mass absorption coefficients). We have developed a technique and windows based computer program which enables the rapid collection of coral density data. The coral skeleton slab is xradiographed with an aluminum wedge. Thickness and density of the aluminum wedge, thickness of the coral slab, density of pure coral aragonite, and digitized images of the coral and wedge x-radiographs provide necessary input. The program uses the wedge image and an empirically determined ratio of relative mass absorption coefficients, (thus removing difficulties with absolute values) in an equation relating wedge optic density and thickness to coral skeletal density. A transect is defined on the coral x-radiograph image, normal to growth band boundaries. Optic density of pixels are converted to skeletal density, averaged, and plotted. Variations of skeletal density along the transect are expressed as peaks and valleys corresponding to high and low density band portions. Measurements of extension, density, and calcification can be calculated for a variety of characterizations of annual and subannual band portions