Limited ecologically relevant genetic connectivity in the south-east African coral populations calls for reef-level management

Estimates of contemporary gene flow between or within marine protected areas along the south-east African coast are required to reveal the degree to which coral communities are self-seeding or otherwise connected. Accordingly, we assessed the ecologically relevant (1 or 2 generations) connectivity of two broadcast spawning coral species, Acropora austera and Platygyra daedalea, on reefs in the region, using two types of hyper-variable genetic markers viz. microsatellites and nuclear introns. Analysis of genetic diversity and differentiation provided evidence for the existence of four discrete genetic populations of A. austera and five of P. daedalea in the sampled area. We found higher genetic diversity on northern South African reefs, which suggests these reefs play a role as sinks for putative migrants. Assignment tests that identified migrants to the South African reefs left some individuals unassigned, but assigned the largest proportion of putative recruits to their source reef, providing evidence of high levels of self-seeding and also of an unsampled source reef. Together, the data indicate that South African populations are, at ecological time scales, independent of gene flow from northern coral populations. The findings suggest that the scope of management needed for the protection of the reefs in the region should not be broad in outlook; each reef should be managed as a single unit, part of the whole rather than representative of the whole.