Modelled Population Level Effects of Ocean Acidification on Two Bivalve Species Using Inverse Demographic Methods

Combustion of fossil fuels releases over eight petagrams of carbon dioxide (CO₂) annually into the atmosphere. About one third of this anthropogenic CO₂ has been absorbed by the oceans, causing CO₂ levels to reach as high as 800 ppm by 2100 (Cao and Caldeira 2008). Estuarine organisms may experience CO₂ levels much higher than those predicted by the end of the century with fluctuations in pH on the order of 1 pH unit occurring daily in some places. Laboratory experiments with larval and juvenile bivalves revealed high mortality and reduced metamorphosis during exposures to elevated levels of CO₂. However, the population consequences of these effects have not been examined. In this study, we created population models to assess the population level impacts of low pH on M. mercenaria (hard clams) and A. irradians (bay scallops). Inverse demographic analysis was used to parameterize population models using field data for each species. CO₂ response functions for growth, survival and fecundity were then substituted into population models to simulate population-level effects. Significant population-level impacts are expected for M. mercenaria and A. irradians. Sensitivity analysis of the integrated population models helped to identify important bottlenecks in population persistence and areas of future research needs.