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

J. S. Grear*, C. A. O’Leary, J. A. Nye, S. T. Tettelbach, C. J. Gobler

*Corresponding author:

ABSTRACT: 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 Mercenaria mercenaria (Northern quahog) and Argopecten irradians (bay scallop). The models were constructed using inverse demography with time series of size-structured field data from NY, 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 five-year projections at pCO2 levels of 400, 800 and 1200 µatm. Although the A. irradians field population exhibited higher growth (12% per year) than the declining M. mercenaria population (-8% per year), cumulative risk was higher due to variance in the stochastic growth rate estimate (log λs = -0.02, σ2 = 0.24). This five-year risk increased from 56% at 400 µatm to 99% and >99% at 800 and 1200 µatm. For M. mercenaria (log λs = -0.09, σ2 = 0.01), five-year 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 responses, 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.