Synergistic effects of elevated CO2 and temperature on the metabolic scope and activity in a shallow-water coastal decapod (Metapenaeus joyneri; Crustacea: Penaeidae)

The physical drivers of climate change (increased CO2; hypercapnia and temperature) are causing increasing warming of the earth's oceans, elevating oceanic CO2 concentrations, and acidity. Elucidating possible climate change impacts on marine biota is of paramount importance, because generally, invertebrates are more sensitive to hypercapnia than fish. This study addresses impacts of synergistic factors; hypercapnia and temperature on osmoregulation, acid base balance, and resting and active metabolism (assessed as oxygen consumption rates) and behavioural performance in a model nektonic crustacean. Metapenaeus joyneri exposed to both hypercapnia (1 kPa) at two temperatures (15 and 20 degrees C) demonstrated significant physiological effects, i.e. new regulatory set points (lower haemolymph osmolality and higher pH, i.e. alkalosis) and reduced metabolic scope (MS), compared with control individuals (normocapnia, 0.04 kPa). Behavioural effects included a significant 30% reduction in swimming ability and may be the result of reduced MS (i.e. difference between active and routine metabolism). Synergistic factors may cause organisms to shift energy utilization towards up-regulation of maintenance functions (i.e. osmoregulatory ability) resulting in a decrease in both aerobic scope and energy-demanding activities. Laboratory-derived evidence elucidating the impacts in key model groups is of paramount importance, if we are to improve our knowledge of physiological effects of synergistic climate change factors.