Saturation-state sensitivity of marine bivalve larvae to ocean acidification

This is an author's peer-reviewed final manuscript, as accepted by the publisher. The published article is copyrighted by Nature Publishing Group, Macmillan Publishers Ltd., and can be found at: http://www.nature.com/nclimate/index.htmlOcean acidification results in co-varying inorganic carbon system variables. Of these, an explicit focus on pH and organismal acid-base regulation in has failed to distinguish the mechanism of failure in highly sensitive bivalve larvae. With unique chemical manipulations of seawater we show definitively that larval bivalve shell development and growth are dependent on seawater saturation state, and not on carbon dioxide partial pressure or pH. Although other physiological processes are affected by pH, mineral saturation state thresholds will be crossed decades to centuries ahead of pH thresholds due to the non-linear changes in the carbonate system variables as carbon dioxide is added. Our findings were repeatable for two species of larval bivalves, could resolve discrepancies in experimental results, are consistent with a previous model of ocean acidification impacts due to rapid calcification in bivalve larvae, and suggest a fundamental ocean acidification bottleneck at early life-history for some marine keystone species