Long-term effects of elevated CO₂ and temperature on the Arctic calanoid copepods Calanus glacialis and C. hyperboreus.

The sensitivity of copepods to ocean acidification (OA) and warming may increase with time, however, studies >10 days and on synergistic effects are rare. We therefore incubated late copepodites and females of two dominant Arctic species, Calanus glacialis and Calanushyperboreus, at 0 °C at 390 and 3000 μatm pCO₂ for several months in fall/winter 2010. Respiration rates, body mass and mortality in both species and life stages did not change with pCO₂. To detect synergistic effects, in 2011 C. hyperboreus females were kept at different pCO₂ and temperatures (0, 5, 10 °C). Incubation at 10°C induced sublethal stress, which might have overruled effects of pCO₂. At 5 °C and 3000 μatm, body carbon was significantly lowest indicating a synergistic effect. The copepods, thus, can tolerate pCO₂ predicted for a future ocean, but in combination with increasing temperatures they could be sensitive to OA.