The transition from the last pelagic larval stage to the first benthic juvenile stage in the complex life cycle of marine invertebrates, such as the American lobster, Homarus americanus, a species of high economic importance, represents a delicate phase in these species development. Under future elevated pCO2 conditions, ocean acidification and other elevated pCO2 events can negatively affect crustaceans. This said their effects on the benthic settlement phase are virtually unknown. This study aimed to identify the cumulative effects of stage IV post-larval exposure to elevated pCO2 levels on the life history and physiology of stage V juvenile lobsters. Post-larval lobsters were exposed to a gradient of current and future pCO2 scenarios that were chosen based on current global ocean conditions (400 μatm) to predicted pCO2 values between now and the end of the century (600, 800, 1000 μatm, IPCC 2014), ecologically relevant coastal pCO2 fluctuations (1200 μatm), and levels potentially achieved from industrial accidents involving carbon capture storage leakages (2000 and 3000 μatm). Daily seawater pH readings were recorded by a pH regulation system (IKS, AquaStar, Karlsbad, Germany) in each tank, and seawater pCO2 was regulated according to these readings. Weekly seawater chemistry contains in situ measurements of the total alkalinity and salinity of seawater samples from one random tank from each pCO2 treatment. Total alkalinity was measured using an open cell potentiometric titration with a full curve Gran end-point determination (Dickson et al., 2007). Carbonate chemistry was then calculated from a combination of the daily pH readings, and the weekly average salinity and total alkalinity of all treatment tanks. The survival, intermoult period, feeding rates, oxygen consumption rates, carapace element composition, and energy metabolism enzyme function of the stage V juvenile lobsters were investigated. Results suggested an increase in mortality, slower development, variable feeding rates, a slight increase in carapace magnesium content, and an increase in aerobic capacity relative to anaerobic capacity with increasing pCO2. Our study points to potential reduction in juvenile recruitment success as seawater pCO2 increases, thus foreshadowing important socio- economic repercussions for the lobster fisheries and industry.
