Coral Propagation\nin Substrates Obtained Through Additive\nManufacturing: Influence of Mortar Formulations on Seawater Parameters

The continued destruction of coral communities has been\na matter\nof concern for the international community. The development of substrates\nand artificial reefs has been an effective restoration method for\nsettling vulnerable coral larvae or for moving juveniles back to natural\nand artificial reefs. This article reveals the potential of different\nmaterials for coral recruitment and propagation substrates that are\nobtained from mineral and organic waste. Three mortars were developed\nwhose compositions include mussel shells, limestone, dolomite sand,\npozzolan materials, and different types of cement. Additive manufacturing\nand silicone molds were used to develop 3D substrate samples with\na complex geometry. This research aims to study how the physical and\nchemical properties of the substrates may affect seawater parameters,\nspecifically pH variations, coral propagation, and the growth rate\nencrusting in both horizontal and vertical directions. Periodic pH\nmeasurements were performed in different volumes of seawater and with\nall of the mortars developed. Additionally, atomic emission spectrometry\nwas used for the determination of different elements (macronutrients,\nmicroelements, and contaminants), over a wide range of concentrations,\nto demonstrate if mortar formulations affect seawater conditions and\nconsequently coral survival and growth. The results demonstrated that\nadditive manufacturing proved to be highly effective in developing\nsubstrates for coral propagation, enabling rapid design adjustments\nin terms of shape, texture, size, and material. Laboratory experimental\nresults demonstrated a significant pH increase in water recipients\nof 50 mL, while in 1000 mL, there was a slight rise, stabilizing over\ntime at 9.1–9.2. The increase in pH is a result of the chemical\ncomposition of Portland limestone cement used in all samples, which\nwas stabilized by using pozzolanic materials. Considering 315 and\n288 days of coral fragments implementation, substrates that incorporate\nmussel shells were most effective for the growth of Montipora danae coral species.