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

Marine invertebrates living in oxygen minimum zones (OMZ), where low pO and high pCO conditions co-occur, display physiological mechanisms allowing them to deal with these coupled stressors. We measured aerobic metabolic rate (MR) and the critical oxygen tension (P), and calculated the oxygen supply capacity (α) of both the red (Grimothea monodon) and yellow (Grimothea johni) squat lobsters, under two pCO scenarios (~414 and 1400 μatm). We also measured haemolymph pH, haemocyanin oxygen binding affinity (p), and haemolymph lactate content in both species under normoxia, low pCO hypoxia and high pCO hypoxia. Our results revealed that both species show extremely low P and P values. The MR increased under high pCO condition in both species but hypoxia tolerance was not negatively impacted by pCO. Furthermore, hypoxia tolerance is enhanced at high pCO in the yellow squat lobster, and although not statically significant, α value follows the same trend. The red squat lobster has a better pH regulation and lower reliance on anaerobic metabolism. While the yellow squat lobster had a poorer pH regulation during high pCO hypoxia, relying more on anaerobic metabolism. Our research suggests that elevated pCO 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.