| Summary: | The red gorgonian Paramuricea clavata is an engineering species, inhabiting rocky shore in the Mediterranean Sea and Portuguese coast of the Atlantic Ocean. The species was severely impacted by climatically induced mass mortality events in the NW Mediterranean. The general aim of the study was to investigate the genetic diversity of P. clavata in the Ligurian Sea (NW Mediterranean), a region highly impacted by past mass mortality events, and the Atlantic Ocean, where mass mortality was never observed due to generally lower water temperature. Microsatellites were used to study the contribution of clonal reproduction, connectivity pattern, genetic structure and diversity. Additionally one mitochondrial marker (Cytochrome Oxidase I) was used to compare the Atlantic and Mediterranean populations. The results revealed, that clonal propagation does not play an important role in P. clavata, since at four out of nine sites clones were not detected and the maximum prevalence of clones reached only 13%. The study failed to detect any genetic diversity loss in the P. clavata populations affected by mass mortality events. The migration pattern among sites affected by mass mortality and unaffected ones was described. The results confirmed that low larval dispersal capability in the red gorgonian may still be ecologically significant for population replenishment and persistence, enabling migration between local populations. This research has identified an important genetic break within the red gorgonian distribution. Both markers used in the present study, mtDNA and microsatellites, revealed the same discontinuity between the Mediterranean and Atlantic. Significant differences were found in the genetic diversity between the Mediterranean and Atlantic populations, with heterozygosity and allelic richness being slightly, but significantly, higher in the Mediterranean Sea, possibly as a result of colonization history or isolation of the Atlantic sites. The differences in genetic diversity were also detected between deep and shallow populations. Allelic richness increase with depth, being lower in the shallow, less stable populations due to past mortality events induced by warming and other interacting factors and higher in deeper, stable populations.The results should prove to be particularly valuable for the conservation of soft corals communities and thus the overall marine biodiversity.
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