Multiple scales of genetic connectivity in a brooding coral on isolated reefs following catastrophic bleaching, Western Australia

Data on the variation of microsatellite markers and changes in coral cover at 6 sites at Scott Reef were used to identify: 1. At which sites were Seriatopora hystrix worst affected by bleaching. 2. The scale of genetic subdivision of S. hystrix at Scott Reef 5 years after the bleaching event, and to what extent had the majority of larvae dispersed (metres or tens of kilometres). 3. Whether new recruits at the most severely bleached sites were produced locally (from a few remaining colonies), from other sites on the same reef, or from other reefs within the Scott Reef system.

All sites consisted of 5 permanent 50 m transects on the reef slope at about 9 m depth. Transects were filmed 6 months before (October 1997), 6 months after (October 1998), and approximately 5 years after (November 2003) a bleaching event which occurred in February 1998. Percentage cover (estimated using a point intercept method) was calculated from the mean percent cover over the 5 transects at each site for each year.

In January 2004, 287 samples from individual colonies of S. hystrix were collected from 6 sites within the Scott system: south Scott (SL1, SL2 and SS1), north Scott (SL4), Sandy Islet Reef (SL5), and Seringapatam Reef (SS3). At each site, the exact location of each sampled colony along a permanent 300 m transect was recorded, along with the global positioning system coordinates at the beginning of each transect. Between 45 and 50 colonies were sampled at regular intervals along each transect.

Genotyping of the 287 individuals was carried out. Because only two pairs of individuals shared the same diploid multilocus genotype, one individual from each of these pairs was removed from subsequent analyses so that each unique genotype was represented only once.

Characteristics of the 9 Seriatopora hystrix microsatellite markers recorded were: the number of unique multilocus genotypes (N), the number of alleles (A), the proportion of observed (HO) and expected (HE) heterozygotes per locus and site, and the FIS calculated for each locus and each site (FIS All). Loci: Sh2-002, Sh2-006, Sh4-001, Sh4-010, Sh3-003, Sh3-004, Sh3-007, Sh3-008, Sh3-009, Sh4-001, Sh4-010. Allelic frequencies, allelic patterns and expected heterozygosities under Hardy-Weinberg equilibrium, and the number of private alleles were calculated in Genalex v6.

Tests for Hardy-Weinberg and linkage disequilibrium were conducted using FSTAT v2.9.3a spatial autocorrelation analysis, applied within each site.