106. The physiology of Polar cod (Boreogadus saida) in a changing world: Impacts of ocean acidification and warming

Kristina L. Kunz (1,2), Guy Claireaux (3), Hans-Otto Pörtner (2), Rainer Knust (1) & Felix C. Mark (2)*

1 Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Bentho-Pelagic Processes, Am Alten Hafen 26, D-27568 Bremerhaven, Germany
2 Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Integrative Ecophysiology, Am Handelshafen 12, D-27570 Bremerhaven, Germany
3 Université de Bretagne Occidentale, LEMAR (UMR 6539), Unité PFOM, Laboratoire ARN, Centre Ifremer de Brest, 29280 Plouzané, France

Background
The oceans are currently experiencing a distinct warming trend concomitant with increasing levels of PCO2. These trends are expected to be most pronounced in Arctic waters due to the high solubility of CO2 in the cold and decreasing salinities in surface waters. Low natural temperatures in the Arctic imply strong adaptation of Arctic species along with reduced tolerance to changing abiotic conditions as a trade-off. Polar cod (Boreogadus saida) is a key species and an important protein source in the Arctic food chain. The aim of the present study is the investigation of several components of the energy budget of Polar cod under current and projected water conditions in order to evaluate its future competitive strength.

Methods
We incubated Polar cod under different combinations of temperature (0, 3, 6, 8°C) and PCO2 (390, 1,170 µatm) over four months and determined growth performance and feed consumption. After their long-term incubation, swimming performance, active (AMR) and standard metabolic rate (SMR) were measured.

Findings
The impact of hypercapnia on the performance of Polar cod was less pronounced compared to temperature effects. Among investigated parameters, swimming performance was the most sensitive towards ocean acidification, indicated by a lower maximum swimming speed. High PCO2 caused a non-significant trend for impaired growth in Polar cod, most pronounced at the optimum temperature for growth (6°C) under control conditions. Despite low feed intake at 0°C, feed conversion efficiency was highest at this temperature. Both AMR and SMR were significantly enhanced at the highest investigated temperature (8°C).

Conclusions
Our results suggest a high sensitivity of Polar cod towards ocean acidification and warming. Decreasing growth rates and swimming performance may parallel a decrease in abundance, especially when OA is combined with further challenges, such as a decline in under-ice habitats and increased Atlantification of Arctic waters.