Abstract
Climate change with increasing temperature and ocean acidification (OA) poses risks for marine ecosystems. According to Pörtner and Farrell [1], synergistic effects of elevated temperature and CO2-induced OA on energy metabolism will narrow the thermal tolerance window of marine ectothermal animals. To test this hypothesis, we investigated the effect of an acute temperature rise on energy metabolism of the oyster, Crassostrea gigas chronically exposed to elevated CO2 levels (partial pressure of CO2 in the seawater ~0.15 kPa, seawater pH ~ 7.7). Within one month of incubation at elevated Pco2 and 15 °C hemolymph pH fell (pHe = 7.1 ± 0.2 (CO2-group) vs. 7.6 ± 0.1 (control)) and Peco2 values in hemolymph increased (0.5 ± 0.2 kPa (CO2-group) vs. 0.2 ± 0.04 kPa (control)). Slightly but significantly elevated bicarbonate concentrations in the hemolymph of CO2-incubated oysters ([HCO− 3]e = 1.8 ± 0.3 mM (CO2-group) vs. 1.3 ± 0.1 mM (control)) indicate only minimal regulation of extracellular acid-base status. At the acclimation temperature of 15 °C the OA-induced decrease in pHe did not lead to metabolic depression in oysters as standard metabolism rates (SMR) of CO2-exposed oysters were similar to controls. Upon acute warming SMR rose in both groups, but displayed a stronger increase in the CO2-incubated group. Investigation in isolated gill cells revealed a similar temperaturedependence of respiration between groups. Furthermore, the fraction of cellular energy demand for ion regulation via Na+/K+-ATPase was not affected by chronic hypercapnia or temperature. Metabolic profiling using 1H-NMR spectroscopy revealed substantial changes in some tissues following OA exposure at 15 °C. In mantle tissue alanine and ATP levels decreased significantly whereas an increase in succinate levels was observed in gill tissue. These findings suggest shifts in metabolic pathways following OA-exposure. Our study confirms that OA affects energy metabolism in oysters and suggests that climate change may affect populations of sessile coastal invertebrates such as mollusks.
Highlights
Coastal zones are ecologically and economically important and are among those areas that will be strongly affected by global climate change
To test this hypothesis we determined the impact of long-term ocean acidification (OA)/hypercapnia on temperature-dependent metabolism by analyzing the acid-base and metabolic status of the Pacific oyster, Crassostrea gigas under conditions simulating a future scenario in which CO2 levels stabilize at ~0.1 kPa PCO2 and water pH decreases by ~0.5 units [45]
Our present study demonstrates that CO2 levels corresponding to expected OA scenarios are likely to interfere with the energy metabolism of oysters
Summary
Coastal zones are ecologically and economically important and are among those areas that will be strongly affected by global climate change. We hypothesized that chronic OA exposure will affect energy metabolism in oysters and will have negative consequences on their temperature tolerance To test this hypothesis we determined the impact of long-term OA/hypercapnia on temperature-dependent metabolism by analyzing the acid-base and metabolic status of the Pacific oyster, Crassostrea gigas under conditions simulating a future scenario in which CO2 levels stabilize at ~0.1 kPa PCO2 and water pH decreases by ~0.5 units [45]. We show that OA exposure leads to a disturbance of acid-base status and changes in the steady-state levels of metabolic intermediates and induces an increase in basal maintenance costs at elevated temperatures These disturbances of energy metabolism indicate that performance and survival of estuarine invertebrates can be affected by even moderate OA scenarios supporting the recommendation by Turley et al [46]
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