Determination of Coral Density Variation and Analysis using X-ray Radiography and 3D Computed Tomography

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Introduction

Coral ecosystems provide great importance to marine life as it give habitat to various marine species, protect coastlines from storms and erosion, and also serve as one of the most biodiverse ecosystem in the planet. Large coral colonies, in particular, can reach ages of several hundred years with extension rates of around 3 - 30 mm per year, and provide information on past climate and environmental parameters 1 . Annual growth bands of coral slabs can allow the reconstruction of the sea environmental conditions by determining the coral density variation using x-ray digital radiography (DR) and 3D computed tomography (CT) 2 . In this study, a standard method for determining the coral density variation from coral slabs using both DR and 3D CT x-ray analyses is presented.

Materials and Methods

Modern and fossil corals obtained from northeastern and northwestern side of the Philippines were slabbed into uniform thickness of 7 mm and subjected to DR and 3D CT x-ray analyses with optimized x-ray parameters. The reconstructed 3D digital volumes were virtually cross-sectioned to expose the variations in density bands and a quantifiable grayscale line profile was used to obtain the coral density variation which helps in determining the sea-surface temperature (SST) experienced by the coral from past tens to hundreds of years with near-daily resolution by correlating it with actual SST data 2 .

Results and Discussion

The determination of the coral density variation was successful using a standard method for the DR and 3D CT x-ray analyses. Each grayscale value corresponds to the variation in density of the coral fossil. Initial results yielded matching satellite data on SSTs of corals.

Conclusions

A standard method on finding the coral density variation was done using DR and 3D CT x-ray analyses. The method was a promising tool for obtaining coral density variations from corral fossils and related materials where pertinent data such as its age, and SST can be obtained which may help predict future sea climate and environmental conditions.