A post-larval stage-based model of hard clam Mercenaria mercenaria development in response to multiple stressors: temperature and acidification severity

Complex biogeochemical processes in the coastal oceans lead to highly variable carbonate chemistry that is further modified by the shifting baseline of pCO(2) caused by ocean acidification. Unfavorable carbonate chemistry, which is pervasive in near-shore, shallow-water deposits, due to high rates of organic matter remineralization and the oxidation of reduced metabolites, has been shown to negatively affect benthic calcifying organisms. For settling infaunal bivalve larvae, such as the hard clam Mercenaria mercenaria, pore waters high in CO2 exert a physiological stress on early post-larval development and homeostasis. The effects of acidification have been shown to increase mortality and reduce calcification for 'just settled' juvenile M. mercenaria, a life stage that heavily affects adult clam abundance. To better understand the effects of acidification and temperature on this sensitive life stage, we constructed a post-larval stage-based development model that investigated how varying degrees of aragonite saturation state affect post-settlement survival of juvenile M. mercenaria. Initial model simulations predict a similar consistency and trend to field experiments that examined the survival of juvenile Mya arenaria residing in buffered and unbuffered sediments. According to our model, the magnitude of acidification had a large effect on post-larval stage duration, which translated to a 60% decrease in total survivors under high variability compared to low variability saturation state scenarios. By modifying temperature-dependent growth rates, we were able to progress juveniles out of the more sensitive life stages faster and, therefore, determined scenarios in which faster growth can reduce exposure to acidification during more sensitive stages.