Effects of Four Substrate Types on Coral Growth Rates

One key challenge in coral reef restoration is the slow growth rate of corals, as coral reproduction is reliant on the size of the colony rather than age. Thus, it is necessary to study factors that contribute to coral growth rates so coral fragments can mature as quickly as possible. One such factor is the substrate that fragments are grown on in ex situ nurseries, commonly referred to as plugs, as both the texture and material of plugs can impact coral growth. The objective of this study was to measure coral growth rates on several plug types to better understand what allows coral fragments to grow faster while also accounting for restoration considerations (e.g., cost). Two common coral species in reef restoration, Acropora palmata (elkhorn coral) and Pseudodiploria clivosa (knobby brain coral) of multiple genotypes were fragmented and glued to four substrate types: grooved ceramic plugs, smooth ceramic plugs, expanded PVC squares, and limestone tiles. Coral growth was monitored for four weeks using buoyant weights and 3D photogrammetry to account for both calcification and surface area measurements. Due to the slow-growing nature of corals and the time constraint of the study, no significant differences were found between any of the substrate types because none of the coral fragments began growing on the substrate. Over time, the Key Largo Coral Nursery will determine which of the four substrates causes the fastest coral growth, as well as different practical considerations that can improve restoration efficiency.