Preserving the viscous coral surface mucus layer using low-acid glycol methacrylate (GMA) resin

The surface mucus layer (SML) is of critical importance in health, disease, and stress responses of corals; however, visualising the intact SML is challenging. Dehydration during histological preparation causes shrinkage and deformation of the mucus gel layer, while fragile, unattached mucus exudates are typically lost altogether. Here, we describe a novel technique using water-soluble glycol methacrylate resin embedding that more accurately preserves the in situ SML. Thickness of the preserved SML is similar to that previously measured on live corals using a glass microprobe. The technique allows microscopic visualisation of the SML structure, as well as thickness and continuity measurements, which are important indicators of SML function in health and disease.