Spatial Strategies in Coral Transplantation: A Systematic Review of Clustered Versus Widespread Configurations

ABSTRACT

Active coral reef restoration incorporates ecological engineering principles. Yet, the spatial arrangement of transplanted colonies, one of the few design parameters directly controlled by practitioners, remains poorly explored empirically. We conducted a systematic review following PRISMA guidelines to evaluate how clustered (high‐density) versus widespread (low‐density) configurations of conspecifics influence restoration outcomes across ecological levels (individual, community, population and ecosystem services). Searches in Scopus and Web of Science retrieved 143 records, of which 15 met the inclusion criteria, a number that itself reflects a critical gap in restoration science. All studies focused on tropical reefs and relied on asexual propagation. Across studies, clustering showed no consistent ecological advantage. Growth responses were highly variable, while survival and coral cover were mostly neutral or negative. Community‐level effects on associated fauna were similarly mixed. Excluding Acropora cervicornis , a naturally thicket‐forming species, further reduced positive responses, underscoring strong species and context dependence. Beyond restoration experiments, evidence from natural communities suggests that clustering can influence fertilization, chimerism, competition, hydrodynamics and habitat cascades. Overall, spatial configuration effects are context‐specific and involve trade‐offs between facilitation and competition and should be tailored to species' life‐history traits and site conditions. Integrating experimentally derived density thresholds into restoration planning could strengthen long‐term outcomes.