Genetic monitoring of deep-water exploited banks of the precious Sardinia coral Corallium rubrum (L., 1758): Useful data for a sustainable management

The precious coral Corallium rubrum is one of the most vulnerable resources in the Mediterranean Sea because of the high levels of human-related and natural mortality rates. The aim of the present study was to document the diversity and connectivity patterns among Sardinian Corallium rubrum populations focusing, in particular, on deep populations (>80m depth) where the commercial exploitation is concentrated. Microsatellite markers revealed high levels of inbreeding, heterozygote deficits, and significant genetic differentiation between and within areas at different depths, with an associated 'isolation by distance' pattern. These results indicated that for precious coral populations in Sardinia the 'deep reef refugia hypothesis', that envisages the capacity for deep corals to act as seed banks for the shallower impaired (over-harvested) populations, is not supported. The highest genetic diversity recorded in Sardinia for all areas and depths with respect to other Mediterranean areas indicates that the strict local management has been effective, since harvesting has not yet led to a substantial erosion of the genetic pool. Possible causes for the high levels of observed diversity in Sardinia are discussed in relation to hydrological conditions, its geographical position and its proximity to some putative glacial refugia. Thus, given the occurrence in Sardinia of highly diverse and differentiated deep-water populations of C. rubrum whose genetic diversity are important for the long-term resilience of the species, the results of the present study strongly support the close monitoring of harvesting, along with the maintenance or even strengthening of the current management and conservation measures (no-take protected areas) already in place in the area.