Acropora austera connectivity in the south-western Indian Ocean assessed using nuclear intron sequence data

The hypervariable carbonic anhydrase 3/550 intron marker was sequenced in order to ascertain the levels of genetic variability and connectivity within and between reefal populations of the hard coral, Acropora austera, on the south-east African coastline. Populations were sampled from (north to south) Bazaruto and Inhaca islands (Mozambique), Rabbit Rock, Two-mile and Red Sands Reefs and Leadsman Shoal (Maputaland, South Africa). Populations at Inhaca Island contained two private alleles, part of the only monophyletic clade with fixed differences between populations in this study. Haplotype and nucleotide diversity were higher in the north of the study area. Indices of migration and haplotype sharing supported significant connectivity between populations in South Africa and Mozambique, which may be important in sustaining genetic diversity in the down-current South African A. austera populations. Measures of population subdivision indicated a significant amount of fixation of allele frequencies amongst populations. Although fine, such differentiation in a marker from the nuclear genome of a hard coral is consistent with some demographic isolation between A. austera populations in southern Mozambique and South Africa. Populations at Rabbit Rock and Inhaca Island were found to be significantly isolated from, and thus less connected to, A. austera populations at other reefs.