Genetic evidence for different scales of connectivity in a marine mollusc

Recent studies of connectivity in marine populations have suggested that larval retention and local recruitment are more common than previously considered. Here we used genetic data to investigate the scale of connectivity and patterns of recruitment in the abalone Haliotis coccoradiata, a broadcast spawner with a short larval stage. Although we detected weak but significant genetic differentiation (F_ST) between populations over a scale of approximately 1000 km, the pattern did not fit an isolation-by-distance (IBD) model, suggesting relatively long dispersal distances. However, individual-based multilocus spatial autocorrelation identified fine-scale genetic structure within a range of 20 km, suggesting short distance dispersal and local recruitment. Simple computer simulations in which all dispersal was restricted to within this scale (mean 10 km) suggested that a significant IBD result would most likely be generated under such a dispersal scenario. The lack of a significant IBD suggests infrequent long-distance dispersal is also likely and this is further supported by oceanographic particle dispersal modelling, which shows that larvae could be transported over large distances by ocean currents. Our results suggest that recruitment occurs primarily over a small spatial scale in a species that also has the ability to disperse over considerably greater distances.