Paulina Bruning

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.

The Antarctic marine environment has a unique geologic and climatic history that has contributed to the evolution of high species diversity. Given the current trend of environmental warming, understanding the history of Antarctic species is crucial for predicting the impact of climate change on ecosystem function. Soft corals are a group of striking presence in the benthic marine assemblages in the Southern Ocean, which is recognized as a biodiversity hotspot. DNA sequences (Cox1, mtMutS, and 28S rDNA) were utilized for molecular phylogenetic reconstructions, species delimitations, and divergence estimations to investigate the spatial patterns of genetic diversity in Alcyonium species in the southern South American‐Antarctic region. Significant genetic divergence was observed between regions, with a clear genetic break between South America and the West Antarctic Peninsula and the identification of four putative species. Divergence time estimates indicated that Alcyonium's diversification began about 41.1 million years ago (Ma), coinciding with the opening of the Drake Passage and the formation of the Antarctic Circumpolar Current (ACC, ~42 Ma). This indicates that Alcyonium has persisted in situ for an extensive period, enduring a wide range of environmental conditions.

Ice scouring is one of the strongest agents of disturbance in nearshore environments at high latitudes. In depths, less than 20 m, grounding icebergs reshape the soft-sediment seabed by gouging furrows called ice pits. Large amounts of drift algae (up to 5.6 kg/m²) that would otherwise be transported to deeper water accumulate inside these features, representing an underestimated subsidy. Our work documents the distribution and dimensions of ice pits in Fildes Bay, Antarctica, and evaluates their relationship to the biomass and species composition of algae found within them. It also assesses the rates of deposition and advective loss of algae in the pits. The 17 ice pits found in the study area covered only 4.2% of the seabed but contained 98% of drift algal biomass, i.e., 60 times the density (kg/m²) of the surrounding seabed. Larger ice pits had larger and denser algal accumulations than small pits and had different species compositions. The accumulations were stable over time: experimentally cleared pits regained initial biomass levels after one year, and advective loss was less than 15% annually. Further research is needed to understand the impacts of ice scouring and subsequent algal retention on ecosystem functioning in this rapidly changing polar environment.