Pelagic early life stages promote connectivity in the demersal labrid Choerodon rubescens

Population connectivity has profound ecological and evolutionary implications. In marine species with complex life cycles, the nature of these implications depends on both the amount of dispersal and the life-cycle stage(s) through which dispersal occurs. For demersal fishes with such life cycles, the pelagic early life stages (ELS) are generally considered the main dispersive phase, though this assumption has rarely been tested. This research investigates genetic connectivity in the reef-dwelling labrid Choerodon rubescens, which is a prized eating fish endemic to ca 1200km of the west coast of Australia. This species has demersal juveniles and adults, and pelagic ELS that are predicted to last about 25–30days. The aim of the study was to use patterns of variation at 12 microsatellite loci to test the hypothesis that C. rubescens is genetically homogeneous across its main distribution. The genetic analyses were based on samples of 26–40 individuals from six locations, which collectively span all of the areas where C. rubescens is common. The values of global FST (0.0019) and DEST (0.0010) were not significantly different from zero and Bayesian clustering indicated that all individuals belonged to a single genetic group. In addition, Mantel tests showed no evidence of isolation by distance. These results support the view that C. rubescens is genetically homogeneous over all or most of its geographic range. Since published otolith microchemistry evidence indicates that the juveniles and adults of C. rubescens are relatively sedentary, these results also imply that the pelagic ELS are the main avenue of dispersal in this species. This study highlights the value of combining the results of complementary methods for assessing the relative importance of the different life-cycle stages in dispersing a fish species. The results also have implications for the management of C. rubescens, which has shown signs of localised overfishing. Specifically, the dispersal of the ELS provides a mechanism for the recruitment of C. rubescens to non-natal reefs. Such connectivity could help this species to recover from localised depletions in abundance and ameliorate the potential evolutionary consequences of any localised overfishing, such as reductions in genetic diversity or selective responses to harvesting.