Energetic plasticity underlies a variable response to ocean acidification in the pteropod, Limacina helicina antarctica

Ocean acidification, caused by elevated seawater carbon dioxide levels, may have a deleterious impact on energetic processes in animals. Here we show that high PCO ₂ can suppress metabolism, measured as oxygen consumption, in the pteropod, L. helicina forma antarctica, by ~20%. The rates measured at 180-380 μatm (MO ₂ = 1.25 M ^-0.25, p = 0.007) were significantly higher (ANCOVA, p = 0.004) than those measured at elevated target CO ₂ levels in 2007 (789-1000 μatm, = 0.78 M ^-0.32, p = 0.0008; Fig. 1). However, we further demonstrate metabolic plasticity in response to regional phytoplankton concentration and that the response to CO ₂ is dependent on the baseline level of metabolism. We hypothesize that reduced regional Chl a levels in 2008 suppressed metabolism and masked the effect of ocean acidification. This effect of food limitation was not, we postulate, merely a result of gut clearance and specific dynamic action, but rather represents a sustained metabolic response to regional conditions. Thus, pteropod populations may be compromised by climate change, both directly via CO ₂-induced metabolic suppression, and indirectly via quantitative and qualitative changes to the phytoplankton community. Without the context provided by long-term observations (four seasons) and a multi-faceted laboratory analysis of the parameters affecting energetics, the complex response of polar pteropods to ocean acidification may be masked or misinterpreted.