Low Pcrit but no hypoxia tolerance? Hypoxia compensation in the Arctic keystone species Boreogadus saida

• Main Authors: Kempf, Sarah, Neven, Carolin J., Claireaux, Guy, Mark, Felix Christopher
• Format: Conference Object
• Language: unknown
• Published: 2022
• Subjects: Arctic; Boreogadus saida; Global warming; polar cod; Sea ice; Svalbard
• Online Access: https://epic.awi.de/id/eprint/57270/; https://hdl.handle.net/10013/epic.e8ace1bc-294e-40bb-aea9-a9270fb7e7e5

Global warming has already caused various environmental changes, including a loss of almost 50% Arctic sea-ice coverage since the 1980s. Sea-ice loss strengthens summer stratification and, consequently, hypoxic zones in the deep-water layers may form. The deep fjord systems of the Svalbard archipelago are particularly at risk from this long-lasting stratification. Thus, the present study aims to investigate the hypoxia tolerance of the Arctic keystone species Polar cod, Boreogadus saida. We measured the respiratory capacity (standard, routine and maximum metabolic rates, SMR, RMR, MMR) and swimming performance under progressive hypoxia (100% to 5% air saturation) at cold habitat temperatures (2.5 °C) and after warm-acclimation to close to its thermal limit (10 °C) via flow-through and swim-tunnel respirometry. The observed metabolic patterns were consistent at both acclimation temperatures: Over its full SMR and partly also MMR ranges, Polar cod displayed oxyregulating behaviour under progressive hypoxia, with SMR never below aerobic baseline metabolism. Despite the common paradigm that polar organisms are not hypoxia tolerant, Polar cod could handle very low oxygen saturations down to a Pcrit of 5.9 % air saturation at 2.5 °C. At 10°C, Pcrit rose to 21.6% air saturation. However, we did not observe any metabolic downregulation and no anaerobic component of the hypoxia response in Polar cod, usually mentioned in the definition of hypoxia tolerance. Therefore, we describe the observed response rather as metabolic hypoxia compensation than hypoxia tolerance as the mechanisms involved here actively seek to improve oxygen supply instead of (anaerobically) tolerating hypoxia through metabolic depression.