Quantifying skeletal density at high temporal resolution in massive scleractinian corals by using two-dimensional grid-scanning gamma densitometry

Abstract

The quantification of skeletal density in massive scleractinians is necessary for a better understanding of skeletal growth in reef-forming corals. However, skeletal density is difficult to quantify and requires sophisticated analytical techniques. In this study, two-dimensional grid-scanning gamma densitometry is used for the first time, to quantify skeletal density fluctuations at higher temporal (intra-annual) resolution as compared to previous annual bulk densities determined with this approach. For testing this application and to evaluate its use for being a tool in coral sclerochronology, a colony of the widespread Atlantic massive coral Orbicella faveolata from the central Belize Barrier Reef (Central America) is herein investigated. In the studied coral, temporal resolution of individual density values corresponds to an approximately bi-weekly resolution. A long-term decline in (intra-)annual skeletal density is observed combined with reduced calcification rates. This indicates a limitation in the capability for skeletal formation in O. faveolata corals within the central Belize Barrier Reef, expressed in reduced skeletal carbonate accretion. In general, time series analyses and statistical correlations of the obtained high-resolution density datasets with skeletal growth patterns (linear extension rates, calcification rates) and geochemical (δ13C, δ18O) data reveal a complex interplay of environmental parameters, which might have controlled the skeletal density in the studied coral.