Molecular, physiological and shell properties of cold-water molluscs (Patellogasteropoda, Nacella spp.) from the Southern Ocean under different environmental conditions: implications for resilience to future climate change

Ocean acidification and warming threaten marine biodiversity, especially calcifying organisms. Species from the Southern Ocean are particularly vulnerable, given the low buffering capacity and high solubility of CO₂ in this area. This study investigated the molecular, physiological and shell properties of two intertidal mollusc species of the genus Nacella (Nacella magellanica and Nacella concinna), collected at five sites between Chilean Patagonia and the Antarctic Peninsula, characterized by variable environmental conditions. The physiological index (Condition Index, CI), transcript expression of HSP70 markers and biometric and skeletal parameters of the shells were evaluated. In N. magellanica, individuals from more stable environments showed a lower expression of HSP70 markers and a higher CI; in N. concinna, gene expression increased under more extreme environmental conditions, without significant changes in CI. At the skeletal level, at sites with higher temperatures, lower pH and lower saturation state (Ω) of aragonite and calcite, shells were thinner, less dense and more porous, suggesting an impact on the biomineralization process. These results suggest that the mechanisms of acclimation to extreme environmental conditions involve a trade-off between physiological stability and adaptive plasticity, making these species ideal for assessing the effects of climate change on the Southern Ocean ecosystems.