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 (MR_a) and the critical oxygen tension (P_crit), 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 P_crit and P₅₀ values. The MR_a 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 pH_e regulation and lower reliance on anaerobic metabolism. While the yellow squat lobster had a poorer pH_e 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.