Author Posting. © The Author(s), 2011. This is the author's version of the work. It is posted here by permission of John Wiley & Sons for personal use, not for redistribution. The definitive version was published in Fish and Fisheries 13 (2012): 182-215, doi:10.1111/j.1467-2979.2011.00424.x. ; Atmospheric carbon dioxide (CO2) emissions from human industrial activities are causing a progressive alteration of seawater chemistry, termed ocean acidification, that has decreased seawater pH and carbonate ion concentration markedly since the Industrial Revolution. Many marine organisms, like molluscs and corals, build hard shells and skeletons using carbonate ions, and they exhibit negative overall responses to ocean acidification. This adds to other chronic and acute environmental pressures and promotes shifts away from calcifierrich communities. In this study, we examine the possible implications of ocean acidification on mollusc harvests worldwide by examining present production, consumption, and export and by relating those data to present and future surface ocean chemistry forecast by a coupled-climate ocean model (Community Climate System 3.1; CCSM3). We identify the “transition decade” when future ocean chemistry will distinctly differ from that of today (2010), and when mollusc harvest levels similar to those of the present cannot be guaranteed if present ocean chemistry is a significant determinant of today’s mollusc production. We assess nations’ vulnerability to ocean acidification-driven decreases in mollusc harvests by comparing nutritional and economic dependences on mollusc harvests, overall societal adaptability, and the amount of time until the transition decade. Projected transition decades for individual countries will occur 10-50 years after 2010. Countries with low adaptability, high nutritional or economic dependence on molluscs, rapidly approaching transition decades, or rapidly growing populations will therefore be most vulnerable to ocean acidification-driven mollusc harvest decreases. These transition decades suggest how soon nations should implement strategies, such as increased aquaculture of resilient species, to help maintain current per capita mollusc harvests. ; This work was supported in part by National Science Foundation grant ATM-0628582, the Climate and Energy Decision Making (CEDM) Center that is supported under a cooperative agreement with the National Science Foundation (SES-0949710), and the Woods Hole Oceanographic Institution Marine Policy Center.