Tracking morphological development in stony corals
The shape of reef-building corals largely determines how they interact with their environment and the ecosystem services they provide. However, morphology is not fixed. As corals grow and develop from singular polyps to mature adult colonies, they experience pronounced changes in their morphology. This developmental trait variation remains poorly quantified in corals, despite their importance as ecosystem engineers. To address this gap, we used photogrammetry to track the morphological development of wild coral colonies across six size-independent metrics designed to capture variation in volume compactness, surface complexity, and top-heaviness. Size-trait models and analyses of colony movement through morphological trait space revealed that small colonies shared compact morphologies and only later diverged along growth-form-specific developmental trajectories. Massive corals largely retained stable shapes as they grew, whereas non-massive colonies became less compact, more top-heavy, and in most cases, more complex. Despite these differences, there was still overlap between growth forms in their developmental trajectories through morphospace. These findings highlight that traditional categorical growth forms mask important developmental variation, particularly early in coral ontogeny. By applying a quantitative trait-based framework, this study improves understanding of coral morphological development and provides a foundation for linking individual growth trajectories to broader reef ecosystem dynamics.