Optimized cleaning and centrifugation of Japanese precious corals for enhanced sclerite classification and chemical profiling

Abstract

The phylum Cnidaria is a vast taxonomic group that includes corals, sea anemones, and jellyfish. This study focuses on corals within the class Octocorallia, order Scleralcyonacea, and family Coralliidae, specifically Corallium japonicum and Pleurocorallium konojoi, which are of ecological and scientific significance in Japan. We evaluated cleaning protocols using sodium hypochlorite and sodium hydroxide to remove organic matter from the biomineralized structures of coral species. The objective was to improve structural integrity preservation, to enable more accurate chemical and structural analyses and contribute to coral restoration efforts. Our findings demonstrated that the most effective cleaning approach for the axial skeleton was the use of 0.4 M sodium hypochlorite (NaClO) solution, immersing the skeleton for 100 min at room temperature (approximately 20 °C). Meanwhile, for the sclerites, the experimental results indicated that the preferred cleaning technique was the use of either 0.1 M or 0.2 M sodium hypochlorite (NaClO) solution for 100 min at room temperature (approximately 20 °C). Additionally, centrifugation of the precious coral sclerites resulted in the clear separation of red and white sclerites. Lastly, we performed chemical analyses on both the skeletons and the sclerites, utilizing ICP-MS and ICP-AES technologies to gain an overview on the concentrations of the major and minor chemical elements that were present in both structures.