| Summary: | Given the vastness of the oceans and the small size of larvae and other marine propagules, tracking marine organisms’ dispersal particles is unrealistic. When propagules successfully recruit, a genetic profile can be tracked that integrates the movements of multiple generations. Molecular analyses thus provide an indirect means of estimating connectivity among subdivided populations, at any given spatial and/or temporal scale of interest. In general, it remains challenging to disentangle the relative influence of the various processes that cause the observed patterns of genetic differentiation among subpopulations, notably in far-off deep-sea environments. In the past decade only a handful of studies have reported on the genetic patterns in Mediterranean cold-water corals. This represents a substantial limitation for any researcher attempting to understand the dynamics of Mediterranean cold-water coral populations. It affects as well conservation decisions involving these vulnerable species and habitats. Until recently, hypotheses for gene flow of some deep-sea corals in the Atlantic have included moderate to high connectivity at broad and regional scales, through sporadic larval transport mediated by ocean currents, and simultaneous strong discontinuities between ocean basinscaused by vicariance or local adaptation. However, progress has been made that is allowing researchers to retrace past major modifications in the patterns of cold-water coral migrations at evolutionary time-scales, in and out of the Mediterranean Sea. Growing evidence of the influence of clonality and its effect on estimates of genetic diversity now stimulate researchers to engage in optimised sampling strategies. Improved estimates are possible to attain, provided a rigorous sampling strategy. Studies of the cosmopolitan corals Lophelia pertusa and Madrepora oculata have made evident that Atlantic populations are clearly differentiated from Mediterranean ones, suggesting that contemporary gene flow between the two genetic backgrounds is ...
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