Effects of coastal acidification on North Atlantic bivalves: Interpreting laboratory responses in the context of in situ populations

Experimental exposure of early life stage bivalves has documented negative effects of elevated pCO2 on survival and growth, but the population consequences of these effects are unknown. We substituted laboratory responses into baseline population models of northern quahog Mercenaria mercenaria and bay scallop Argopecten irradians. The models were constructed using inverse demography with time series of size-structured field data from New York, USA, whereas the stress-response relationships were developed using data from published laboratory studies. We used stochastic projections and diffusion approximations of extinction probability to estimate cumulative risk of 50% population decline during 5 yr projections at pCO2 levels of 400, 800, and 1200 μatm. Although the A. irradians field population exhibited higher growth (12% yr-1) than the declining M. mercenaria population (-8% yr-1), cumulative risk was higher due to variance in the stochastic growth rate estimate (log λs = -0.02, σ2 = 0.24). This 5 yr risk increased from 56% at 400 μatm to 99 and >99% at 800 and 1200 μatm, respectively. For M. mercenaria (log λs = -0.09, σ2 = 0.01), 5 yr risk was 25, 79, and 97% at 400, 800, and 1200 μatm, respectively. These estimates could be improved with detailed consideration of harvest, disease, restocking, compensatory re sponses, and interactions between these and other effects. However, results clearly indicate that early life stage responses to plausible levels of pCO2 enrichment have the potential to cause significant increases in risk to these marine bivalve populations