The effects of elevated temperature and P CO2 on the energetics and haemolymph pH homeostasis of juveniles of the European lobster, Homarus gammarus.

Regulation of extracellular acid-base balance, while maintaining energy metabolism, is recognised as an important aspect when defining an organism's sensitivity to environmental changes. This study investigated the haemolymph buffering capacity and energy metabolism (oxygen consumption, haemolymph [l-lactate] and [protein]) in early benthic juveniles (carapace length <40 mm) of the European lobster, Homarus gammarus, exposed to elevated temperature and P CO2 At 13°C, H. gammarus juveniles were able to fully compensate for acid-base disturbances caused by the exposure to elevated seawater P CO2  at levels associated with ocean acidification and carbon dioxide capture and storage (CCS) leakage scenarios, via haemolymph [HCO3 -] regulation. However, metabolic rate remained constant and food consumption decreased under elevated P CO2 , indicating reduced energy availability. Juveniles at 17°C showed no ability to actively compensate haemolymph pH, resulting in decreased haemolymph pH particularly under CCS conditions. Early benthic juvenile lobsters at 17°C were not able to increase energy intake to offset increased energy demand and therefore appear to be unable to respond to acid-base disturbances due to increased P CO2  at elevated temperature. Analysis of haemolymph metabolites suggests that, even under control conditions, juveniles were energetically limited. They exhibited high haemolymph [l-lactate], indicating recourse to anaerobic metabolism. Low haemolymph [protein] was linked to minimal non-bicarbonate buffering and reduced oxygen transport capacity. We discuss these results in the context of potential impacts of ongoing ocean change and CCS leakage scenarios on the development of juvenile H. gammarus and future lobster populations and stocks.