Dispersal distances for shallow Agaricia corals

Understanding the dispersal potential of different species is essential for predicting recovery trajectories following local disturbances and the potential for adaptive loci to spread to populations facing extreme environmental changes. However, dispersal distances have been notoriously difficult to estimate for scleractinian corals, where sexually- (as gametes or larvae) or asexually- (as fragments or larvae) derived propagules disperse through vast oceans. Here, we demonstrate that mean dispersal distances for sexually-produced propagules can be indirectly inferred for corals using individual-based isolation-by-distance (IbD) analyses by combining reduced-representation genomic sequencing with photogrammetric spatial mapping. Colonies from the genus Agaricia were densely sampled across plots at four locations and three depths in Curaçao. Seven cryptic taxa were found among the three nominal species (Agaricia agaricites, Agaricia humilis and Agaricia lamarcki), with four taxa showing generational dispersal distances within metres: two taxa within A. agaricites and two within A. humilis. The short distances estimated here imply that shallow Agaricia populations are reliant on highly localised replenishment and demonstrate the need to estimate dispersal distances quantitatively for more coral species.