Blood O2 affinity of a large polar elasmobranch, the Greenland shark Somniosus microcephalus

• Published in: Polar biology 2017-11, Vol.40 (11), p.2297-2305
• Main Authors: Herbert, N. A., Skov, P. V., Tirsgaard, B., Bushnell, P. G., Brill, R. W., Harvey Clark, C., Steffensen, J. F.
• Format: Article
• Language: English
• Subjects: Affinity; Binding; Biomedical and Life Sciences; Blood; Body mass; Climate change; Ecology; Evaluation; High temperature; Life Sciences; Marine fishes; Metabolic rate; Metabolism; Microbiology; Oceanography; Original Paper; pH effects; Physiology; Plant Sciences; Sensitivity; Sharks; Somniosus microcephalus; Swimming; Temperature; Temperature effects; Vulnerability; Zoology
• ISSN: 0722-4060; 1432-2056
• DOI: 10.1007/s00300-017-2142-z

The Greenland shark ( Somniosus microcephalus . Bloch & Schneider 1801) is a polar elasmobranch that is hypothesised to possess a unique metabolic physiology due to its extreme large size, the cold waters it inhabits and its slow swimming lifestyle. Our results therefore provide the first insight into the metabolic physiology of this unique shark, with a focus on blood O 2 affinity. An evaluation of blood O 2 affinity at 2 °C using tonometry revealed a P 50 of 11.7 mmHg at a P CO 2 of 2.25 mmHg and a Bohr effect (binding sensitivity of blood to pH, ϕ = Δlog P 50 /ΔpH) of −0.26. A comparative evaluation of blood O 2 affinity across elasmobranch fishes suggests that S. microcephalus has a high blood O 2 affinity (i.e., low P 50 ) and a small Bohr effect but these are common traits in sluggish elasmobranch fishes, with little evidence for any relationship of blood O 2 affinity to the low metabolic rates, low environmental temperatures, or large body mass of S. microcephalus . After gathering this physiology data, a subsidiary aim attempted to understand whether a warming scenario would impose a negative effect on blood O 2 binding. Incubating blood to a slightly elevated temperature of 7 °C resulted in a small but significant reduction of blood O 2 affinity, but no significant change in the Bohr effect. The Hill’s cooperativity coefficient ( n H ) was also small (1.6–2.2) and unaffected by either P CO 2 or temperature. The moderate sensitivity of Greenland shark blood O 2 affinity to warming potentially implies little vulnerability of functional O 2 supply to the temperature changes associated with the regular vertical movements of this species or warming of polar seas resulting from directional climate change.