Tropical Eastern Pacific coral morphometrics: a toolkit for coral studies

In the Eastern Tropical Pacific (ETP), colonies of the genus Pocillopora dominate reef frameworks and are widely used in restoration initiatives. However, the considerable degree of phenotypic plasticity of these corals together with overlapping morphologies blurs the link between colony morphology and species identity, making it difficult to quantify species-level morphofunctional contributions. Here, we address this challenge by applying three-dimensional (3D) digitisation techniques to characterise the morphofunctional space of ETP coral species. 3D digitisation techniques have been demonstrated to facilitate precise estimation of morphofunctional traits. However, their application in the ETP remains constrained. In this study, we delineate the morphofunctional space of ETP coral species for the first time using 206 3D models from nine coral species (including both massive and branching forms) and six morphofunctional traits: sphericity, convexity, packing, rugosity, and the first moments of area and volume. A principal component analysis demonstrated that packing and sphericity accounted for the majority of observed morphological variation, differentiating massive corals from branching Pocillopora morphologies. Discriminant analysis further revealed high morphological redundancy within the Pocillopora species complex. It was possible to construct a series of mathematical models using colony maximum diameter or planar area to estimate a suite of morphofunctional traits. The construction of these models was made possible by leveraging this redundancy. These model equations become a toolkit that provides an accessible framework for integrating morphofunctional metrics into ecological assessments and restoration monitoring in the ETP, thereby improving our ability to evaluate functional recovery and the consequences of shifts in coral assemblages.