The Antarctic marine environment has a unique geologic and climatic history that has contributed to the evolution of a diverse range of species. With the environment undergoing warming trends, it is critical to understand the history of Antarctic species to anticipate the effect of environmental changes on ecosystem functioning. Soft corals are a crucial component of the benthic marine assemblage of the Southern Ocean, which is recognized as a biodiversity hotspot. Nevertheless, our comprehension of the biogeographical patterns and distribution of this group in the Southern Ocean is insufficient. In this study, we used molecular phylogenetic reconstructions, divergence estimations, and species delimitations to examine the spatial patterns of genetic diversity in shallow-sea octocorals of the Alcyonium spp. in the Southern Ocean and adjacent regions, utilizing DNA sequences (mtMutS-COI and 28S) and Genomic Single Nucleotide Polymorphisms (SNPs) markers. The study revealed significant genetic differences between different populations, with a clear genetic break observed between SA and WAP populations. We also identified four putative species or evolutionary independent units (EIUs), with one putative species found in the West Antarctic Peninsula, one in the Patagonian region, and two found in Burdwood Bank and Falkland Island, respectively. The divergence time estimation indicated that the diversification process of Alcyonium began about 7.2 million years ago, with the initial separation occurring between WAP and SA populations. Furthermore, the study emphasized the critical role played by the Scotia Sea islands, especially Burdwood Bank, in the evolution of Southern Ocean biota. Overall, the findings provide evidence for the existence of multiple species within the genus Alcyonium and information on the evolutionary history of this group for the first time in the Southern Ocean.

Almost all collections were obtained through SCUBA diving, at depths varying between 5 m to 40 m on rocky substratum. In the case of BB sampling, a mini–Agassiz Trawl (AGT) with a mouth width of 1.25 m and a mesh size of 1 cm was used to collect specimens at a depth of 395 m. After collection, specimens were photographed in the laboratory. Subsequently, they were preserved in 70% ethanol for DNA analysis and fixed in 90% ethanol for taxonomic examination. Taxonomic description was done based on consistent differences observed in sclerite morphology and colony growth form, using the criteria described by (Van Ofwegen et al., 2007). For DNA analysis two molecular approaches were used: (1) Mito-nuclear genes and (2) Single Nucleotide Polymorphisms (SNPs).

dartR V.1.1.11 package