Population genetics of a habitat-forming scleractinian coral in the mesophotic and deep-sea of the Red Sea

Understanding the connectivity of species is fundamental to identifying population units and implementing conservation actions. During the last years, population genetic patterns of shallow (less than 30 m depths) reef taxa have been increasingly investigated in the Red Sea, providing evidence of dispersal breaks and the role of environmental gradients in shaping the distribution and connectivity of shallow-water reef organisms. Nevertheless, dynamics for the mesophotic and deep-sea fauna remain largely unexplored in this basin. Here, we collected coral colonies of the habitat-forming species Dendrophyllia sp. at depths between 78 and 344 m across nine areas of the Saudi Arabian Red Sea, covering 1,400 km of overwater distance, from the Gulf of Aqaba to the Farasan Islands. By applying a Restriction-site Associated DNA Sequencing (RADseq) approach, we gathered genetic information on 62 individuals at 7,247 putatively neutral SNPs. Population structure analyses suggested the presence of two distinct clusters, a northern and a southern one, with individuals collected at latitudes between 20.5N and 22.0N showing an admixed signal with a major assignment to the southern cluster. The genetic connectivity of the scleractinian Dendrophyllia sp. was strongly determined by an isolation by distance pattern while, considering environmental parameters, differences in dissolved oxygen concentration, rather than in salinity and temperature, correlated with the population differentiation. Out of the 29 candidate outlier SNPs potentially under selection between the two clusters, we found loci putatively involved in energy metabolic processes and response to stress, including for example hypoxia. This study represents the first population genetic assessment of a deep-sea taxon of the Red Sea and suggests that the peculiar geological, ecological, and environmental conditions in the Farasan Banks (southern Red Sea) may influence the dispersal of the investigated coral species. Furthermore, these results provide basic knowledge for the identification of large-scale mechanisms determining the connectivity of deep-sea benthic organisms in the Red Sea to better inform monitoring and conservation strategies.