Colony compactness predicts growth and survival in corals

Kyle J A Zawada , Andrew H Baird, Tom Bridge, Sean R Connolly, Joshua S. Madin , Maria Dornelas

Understanding differences in growth and survival rates across species is a key element of anticipating how ecosystems are likely to respond to global change. However, measuring vital rates for highly diverse assemblages with many rare species is often unfeasible. Identifying links between traits and vital rates that apply across entire groups of species can provide a way to infer assemblage-wide demographic variation at the same time as identifying how traits relate to life history strategies. We combined 3D models of coral colonies with field measured vital rates to explore how mortality and growth vary with colony size and three morphological traits: sphericity, convexity and surface area to volume ratio. We showed that sphericity is negatively related to size-specific mortality and positively related to variation in net growth across a representative range of colony shapes. Further, sphericity significantly modulates size-demography relationships as colony size increases. Sphericity consistently outperformed surface area to volume ratio, highlighting that morphological compactness is a key driver of life history strategies that is independent of colony size. These results suggest that variation in colony compactness in an important axis of demographic strategy differentiation in corals.