Fine-scale genetic structuring in Corallium rubrum:: evidence of inbreeding and limited effective larval dispersal

The red coral Corallium rubrum has a long history of intensive exploitation. As a consequence, most populations have been overharvested, which may be leading to reduced levels of genetic diversity. C. rubrum is a gorgonian distributed in the Mediterranean Sea and along the neighbouring Atlantic coasts, with brooding larvae which disperse only over short distances. Such limited dispersal of larvae suggests that gene flow is restricted in this species, but no experimental evidence is et available. In the present study, small spatial scale genetic structuring was analysed in C. rubrum samples collected in the Ligurian Sea using a hierarchical sampling design, including scales from 10s to 100s of metres. The genetic variation of each colony was analysed using 4 microsatellite loci. Significant deviations from Hardy-Weinberg equilibrium due to elevated heterozygote deficiencies were detected in all samples and were consistent with the occurrence of inbreeding and a Wahlund effect. Significant levels of genetic differentiation were found both between locations (F-ST = 0.209 +/- 0.02) and among samples within each location (F-ST range = 0.025 to 0.082). Our results indicate the occurrence of significant genetic structuring at spatial scales of 10s of metres, supporting the hypothesis that planulae have a limited effective dispersal ability. The occurrence of structured breeding units and differences in genetic diversity among samples also suggest that strategies for sustainable management and conservation of red coral should be defined at a local scale.