Does historical harvesting affect colony size distribution and genetic diversity in Corallium rubrum (Linnaeus, 1758)? Evidences from the Southern Mediterranean commercial banks

The precious octocoral Corallium rubrum has a long history of exploitation in the Mediterranean Sea. Historically, harvesting followed the boom and bust cycles whereby newly discovered beds were overexploited to depletion. In the past, most of the red coral harvesting came form France, Italy, and Spain. Today, landing data show that Tunisia is the third largest supplier of C. rubrum. The aim of this study was to asses whether and how the exploitation effort affects size distribution and genetic diversity of Tunisian commercial populations. Biometric data and microsatellite markers were used to characterize 113 colonies collected on nine commercial banks. Size and branching pattern indicate that collected colonies are up to 100 years old with a high reproductive rate. Nevertheless, 38% of the colonies were undersized according to FAO-GFCM recommendations (basal diameter < 7 mm). Tunisian populations showed a weak genetic structuring and significant differentiation between coastal and offshore populations. Harvesting did not alter the structure of red coral populations. However, technological improvement and intensive harvesting of Tunisian banks, if not properly managed, may lead to their rapid depletion, causing long-lasting shifts in population demography and genetic structure, and the loss of this valuable resource.