Contrast-enhanced micro-XCT as a tool for organismal and reproductive trait observations in corals based on scans of Thesea nivea Deichmann, 1936

Micro-X-ray computed tomography (micro-XCT) with contrast enhancement is considered a non-destructive tool that is increasingly being applied to explore the internal and external structures of vertebrates and invertebrates. Although micro-XCT has been applied to corals to study skeletal features, contrast enhancement has not been tested to explore the soft tissue structures of corals. This study is the first to explore the utility of contrast enhancement advance octocoral systematics by testing whether internal and external features, including soft tissue features, of the octocoral Thesea nivea can be visualized after contrast staining with 2.5% Lugol’s iodine. Contrast staining permitted visualization of soft tissues with sufficient density differences among tissues to distinguish skeletal elements, dermal layers, polyp internal structures, and oocyte stages and features. Further optimization of this approach could enhance its utility for systematics and increase its efficiency through development of semi-automated pipelines for morphometric and histological analyses. Highlights Contrast-enhanced micro-XCT proves useful for octocoral systematics. Organismal and histological information for T. nivea was visualized with contrast. Sufficient density differences were observed to differentiate among soft tissues.