Diel vertical migration of the Southern Ocean euphausiid, Euphausia triacantha, and its metabolic response to consequent short-term temperature changes

Diel vertical migration is a widespread behaviour amongst zooplankton, yet its effect on the rate at which individuals respire remains poorly understood. To address this, we investigated the effect of short-term temperature change on the respiration rate of Euphausia triacantha, a common component of the Southern Ocean zooplankton and a prominent vertical migrator. We found respiration to vary in response to size, with a value of 0.84 for the scaling coefficient, b. When scaled to b, respiration varied strongly in response to transitory temperature change, ranging from 0.37 to 1.65 µl O2 mg dry weight (DW)-b h-1 between 0.17 and 4.74°C, resulting in a Q10 of 3.6. This Q10 is higher than found by other studies examining the short-term respiration response of euphausiids, including those taking a multi-species perspective. This indicates that E. triacantha shows little compensation during short-term exposure to temperatures normally encountered during migration. Furthermore, it shows a distinct metabolic cost to diel vertical migration (DVM) when substantive changes in temperature are encountered over the course of the transit. This temporal variability in respiration rate has important implications for how community respiration is estimated, and for our understanding of DVM behaviour. Our results also have particular relevance to estimating the flux and sequestration of respiratory products, such as dissolved carbon dioxide, to and within the ocean interior.