Multiscale genetic connectivity, kinship, and demographic history of the Antarctic soft coral Alcyonium antarcticum in the Western Antarctic Peninsula

Rapid environmental change and a complex glacial history in the Western Antarctic Peninsula (WAP) have likely shaped the structure and persistence of Antarctic benthic species, yet connectivity remains poorly resolved for key habitat‑forming taxa. Understanding spatial genetic structure in these species is essential to predict their resilience and to inform conservation in this rapidly warming region. Here, we used genome‑wide SNPs to assess connectivity in the Antarctic soft coral Alcyonium antarcticum across multiple spatial scales along the WAP, sampling 90 individuals from three regions spanning the northern, central, and southern peninsula, with additional local and fine‑scale sampling within King George Island. Using DArTseq‑derived SNPs and a hierarchical sampling design, we analysed genetic diversity, population structure, and gene flow across large (hundreds of kilometers), local (kilometers), and fine (meters) spatial scales. At the large scale, three genetic clusters corresponding to Adelaide, Doumer, and King George islands indicated strong structure consistent with persistent historical and oceanographic barriers. At the local scale, significant differentiation, isolation by distance, and high self‑recruitment revealed weakly connected subpopulations, while at the fine scale the absence of clones indicated predominantly sexual reproduction with limited larval dispersal. Genetic diversity was lower than in temperate and tropical octocorals, consistent with glacial bottlenecks. Overall, A. antarcticum forms highly structured and weakly connected populations, highlighting the need to protect multiple demographically independent populations in the rapidly warming WAP.