ALLOZYME VARIATION IN MARGINOPORA-VERTEBRALIS (FORAMINIFERA, MILIOLIDAE) FROM CORAL-REEF HABITATS IN THE GREAT-BARRIER-REEF, AUSTRALIA

Allozyme variation at four loci was examined in Marginopora vertebralis populations from reef flat and lagoon habitats in two reefs in the central Great Barrier Reef. No significant genetic differentiation was observed between habitats or between reefs. The highly significant genetic differentiation observed between replicate samples within only one habitat was the result of the abundance of a second clone at one site on Davies reef flat and did not reflect a consistent pattern of spatial differentiation within habitats. No evidence suggested that different sibling species, or indeed different clones, were present in different habitats. The low genetic distance (average Nei's D = 0.017, highest < 0.057) indicated high gene flow among populations up to 100 km apart. Shallow water habitats suitable for M. vertebralis between segments of the Great Barrier Reef may provide a route for gene exchange between populations. Phenetic analyses of banding patterns for esterase provided similar evidence of a high degree of homogeneity between the populations sampled. Significant heterozygote deficits in most samples showing variation was consistent with a high degree of asexual reproduction in M. vertebralis.