| Summary: | Areas of the Arctic Ocean are already experiencing seasonal variations of low pH and elevated pCO2, with the entirety of the Arctic Ocean expected to be the most affected by ocean acidification (OA) in the very near future. As one of the most abundant first order consumers, Arctic krill, play an important ecological role within Arctic ecosystems. Therefore, understanding krill responses to low pH conditions have important implications for these ecosystems. However, very little is known about their responses to Arctic Ocean acidification. This study examined natural fjord seawater chemistry conditions in early spring as well as overwintering individuals of Thysanoessa inermis’s biological response to a range of low pH conditions. We explored the impacts of OA on oxygen consumption rates (as a proxy for standard metabolic rate), adenosine triphosphate (ATP), l-lactate and fatty acid composition. Thysanoessa inermis was incubated for 7 d in a range of low pH conditions (7.85, 7.75, 7.45) with an ambient control of 8.12. Our data revealed that across the range of low pH investigated there was no significant impact on krill biology. Our observations of natural seawater chemistry conditions showed a 0.3 unit difference in pH throughout the fjord. The results suggest that overwintering Thysanoessa inermis may have a tolerance to low pH due to the natural fjord conditions they experience. In collaboration with Plymouth Marine Laboratory (PML), Plymouth, Devon, UK
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