Genetic isolation and loss of diversity in the broadcast spawning coral, Acropora kenti at Yunbenun (Magnetic Island) on the Great Barrier Reef

Abstract Coral populations on inshore reefs of the Great Barrier Reef (GBR) face increasing pressures from environmental stressors. Genetic diversity and connectivity are key determinants of coral adaptive capacity. Acropora kenti forms at least four genetically distinct clusters distributed across hundreds of kilometres along the GBR. One cluster which is potentially vulnerable due to restricted geographic distribution is found at Yunbenun (Magnetic Island). Here, we conducted a genetic assessment of A. kenti populations from seven reefs around Yunbenun and eight adjacent inshore and mid-shelf reefs in the central GBR to identify their population structure, genetic diversity and connectivity. Using single nucleotide polymorphisms (SNPs) we demonstrate that a genetically distinct (F st >0.33) lineage dominates at all bays around Yunbenun but is rarely found on adjacent reefs. Fine-scale analysis within the Yunbenun lineage revealed a pattern of isolation by distance, driven by limited gene flow. Admixture analysis supported by hydrodynamic modelling shows that larval dispersal is occurring between Yunbenun and surrounding reefs, but gene flow remains limited. Populations at Yunbenun have lower allelic richness ( p < 0.001) and much lower effective population sizes (N e = 1348 (northern bays), N e = 91 (southern bays)) compared with adjacent reefs (N e = 9494). These findings demonstrate that although the genetic diversity of A. kenti across the GBR remains high, isolated and potentially locally adapted populations such as those at Yunbenun may be at risk of genetic decline, undermining their adaptive potential and increasing their conservation concern.