Effects of elevated CO2 on the critical oxygen tension (Pcrit) and aerobic metabolism of two oxygen minimum zone (OMZ) hypoxia tolerant squat lobster species.

Marine invertebrates living in oxygen minimum zones (OMZ), where low pO2 and high pCO2 conditions co-occur, display physiological mechanisms allowing them to deal with these coupled stressors. We measured aerobic metabolic rate (MRa) and the critical oxygen tension (Pcrit), and calculated the oxygen supply capacity (α) of both the red (Grimothea monodon) and yellow (Grimothea johni) squat lobsters, under two pCO2 scenarios (~414 and 1400 μatm). We also measured haemolymph pH, haemocyanin oxygen binding affinity (p50), and haemolymph lactate content in both species under normoxia, low pCO2 hypoxia and high pCO2 hypoxia. Our results revealed that both species show extremely low Pcrit and P50 values. The MRa increased under high pCO2 condition in both species but hypoxia tolerance was not negatively impacted by pCO2. Furthermore, hypoxia tolerance is enhanced at high pCO2 in the yellow squat lobster, and although not statically significant, α value follows the same trend. The red squat lobster has a better pHe regulation and lower reliance on anaerobic metabolism. While the yellow squat lobster had a poorer pHe regulation during high pCO2 hypoxia, relying more on anaerobic metabolism. Our research suggests that elevated pCO2 is crucial on respiratory processes in hypoxia tolerant organisms, ameliorating the effects of hypoxia alone. Learning from OMZ adapted species contribute to better predicting climate change consequences on these important ecosystems.