Concordant Patterns of Population Genetic Structure and Symbiont Communities in a Broadcasting Spawning Coral Along a...

The degree of connectivity across ecosystems is a key determinant of resilience, directly influencing recovery potential after disturbance and long-term ecosystem stability. In reef-building corals, there is added complexity to these processes because both the coral host and their symbiotic dinoflagellates determine resilience. Given these complexities, we investigated the connectivity of a broadcast spawning coral and its associated algal symbiont communities along the Ningaloo Reef Marine Park and Muiron Island Management Area. Using reduced representation sequencing and DNA metabarcoding in 158 colonies of Acropora cf. tenuis across 14 sampling sites, we detected significant spatial genetic structure in the coral host consistent with a pattern of isolation by distance (IBD). Spatial Autocorrelation analyses revealed that the genetic neighbourhood extends up to 50 km suggesting that this coral species has multiple demographically independent populations across Ningaloo Reef. Symbiont communities were dominated by Cladocopium and followed a similar IBD pattern of between-site differences in community composition. We did not identify a significant correlation between host genetic diversity and symbiont community diversity at the colony level. However, spatial patterns of genetic differentiation between sample sites for the host and symbiont community composition were significantly associated suggesting that connectivity along a fringing reef system for both coral hosts and their symbionts is driven by similar biogeographic factors.