Abstract: This research examines the effects of ocean acidification on embryos and larvae of a contemporary calcifier in the coastal waters of Antarctica, the sea urchin Sterechinus neumayeri. The effect of future ocean acidification is projected to be particularly threatening to calcifying marine organisms in coldwater, high latitude seas, making tolerance data on these organisms a critical research need in Antarctic marine ecosystems. Due to a high magnesium (Mg) content of their calcitic hard parts, echinoderms are especially vulnerable to dissolution stress from ocean acidification because they currently inhabit seawater that is barely at the saturation level to support biogenic calcification. Thus, cold-water, high latitude species with a high Mg-content in their hard parts are considered to be the 'first responders' to chemical changes in the surface oceans. Studies in this proposal will use several metrics to examine the physiological plasticity of contemporary urchin embryos and larvae to CO2-acidified seawater, to mimic the scenarios defined by IPCC models and by analyses of future acidification predicted for the Southern Ocean. The research also will investigats the biological consequences of synergistic interactions of two converging climate change-related stressors - CO2- driven ocean acidification and ocean warming. Specifically the research will (1) assess the effect of CO2-acidified seawater on the development of early embryos and larvae, (2) using morphometrics, examine changes in the larval endoskeleton in response to development under the high-CO2 conditions of ocean acidification, (3) using a DNA microarray, profile changes in gene expression for genes involved in biomineralization and other important physiological processes, and (4) measure costs and physiological consequences of development under conditions of ocean acidification. The proposal will support the training of undergraduates, graduate students and a postdoctoral fellow. The PI also will collaborate with the UC Santa Barbara Gevirtz Graduate School of Education to link the biological effects of ocean acidification to the chemical changes expected for the Southern Ocean using the 'Science on a Sphere' technology. This display will be housed in an education and public outreach center, the Outreach Center for Teaching Ocean Science (OCTOS), a new state-of-the-art facility under construction at UC Santa Barbara.