Abstract
The ability of coral reefs to recover from natural and anthropogenic disturbance is difficult to predict, in part due to uncertainty regarding the dispersal capabilities and connectivity of their reef inhabitants. We developed microsatellite markers for the broadcast spawning gorgonian octocoral E unicea ( P lexaura ) flexuosa (four markers) and its dinoflagellate symbiont, S ymbiodinium B 1 (five markers), and used them to assess genetic connectivity, specificity and directionality of gene flow among sites in F lorida, P anama, S aba and the D ominican R epublic. Bayesian analyses found that most E . flexuosa from the F lorida reef tract, S aba and the D ominican R epublic were strongly differentiated from many E . flexuosa in P anama, with the exception of five colonies from K ey W est that clustered with colonies from P anama. In contrast, S ymbiodinium B 1 was more highly structured. At least seven populations were detected that showed patterns of isolation by distance. The symbionts in the five unusual K ey W est colonies also clustered with symbionts from P anama, suggesting these colonies are the result of long‐distance dispersal. Migration rate tests indicated a weak signal of northward immigration from the P anama population into the lower F lorida Keys. As E . flexuosa clonemates only rarely associated with the same S ymbiodinium B 1 genotype (and vice versa), these data suggest a dynamic host–symbiont relationship in which E . flexuosa is relatively well dispersed but likely acquires S ymbiodinium B 1 from highly structured natal areas prior to dispersal. Once vectored by host larvae, these symbionts may then spread through the local population, and/or host colonies may acquire different local symbiont genotypes over time.