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UBC Theses and Dissertations

Upper thermal limits and acclimation potential of Arctic cod (Boreogadus saida) : a key food web species in the Arctic Ocean Drost, Helen E.


The recent rapid and unprecedented changes to the physical and biogeochemical properties of the Arctic Ocean have gained worldwide attention. The greater than 50% reduction in sea ice volume below average is of great concern. My thesis investigates the potential effects of a warmer Arctic Ocean upon the indigenous Arctic cod, Boreogadus saida. This fish make up a significant proportion of the lower trophic energy reserve available in Arctic marine systems. Predators rely upon Arctic cod to provide them bite sized access to those critical energy reserves. Yet despite their key role in the Arctic food web, their upper thermal limits are not well studied. Thus, my three objectives were: a) quantify, for the first time in this species, their upper thermal limits b) determine the acclimation potential of the species at three acclimation temperatures and c) contrast the results generated by different methods that quantify thermal limits for declining physiological performance (rate transition temperatures) that I determined. Boreogadus saida upper thermal limits were tested under acute warming conditions using three different methods: loss of equilibrium (Tcmax), absolute aerobic scope (AAS) derived from oxygen uptake rates and the cardiac method, which uses maximum heart rate (ƒHmax) to detect change in whole animal performance. In conducting the thermal acclimation studies, I discovered foremost that 6.5°C-acclimated fish grew at that temperature but, to date, have only produced eggs at 3.5°C water temperatures. The Tcmax significantly increased with acclimation temperature (0.5, 3.5 and 6.5°C) from 14.4, 15.5, up to 17.1°C respectively, while the more ecologically relevant AAS transition temperature limits were found at lower temperatures from 1.0 to 5.5°C. The temperature for peak ƒHmax (Tmax) occurred between 11.0 to 12.0°C and the performance of ƒHmax for larval B. saida during acute warming was not significantly different from the adults until Tmax was reached. This novel study of the thermal physiology of this key Arctic marine food web species revealed a greater than expected thermal tolerance and a significant acclimation potential up to 6.5°C, suggesting that this species may be more resilient to rapid climate change than previously thought.

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