Effect of in-situ simulated light levels on respiration rate of <italic>Euphausia superba</italic> in winter

Abstract

As the key species in the Southern Ocean, how Antarctic krill (<italic>Euphausia superba</italic>, hereafter krill) survives through the extremely severe winter time is always one of the key issues for krill ecology. Krill can utilize different strategies to tackle the long winter time, and in which the most effective pattern is to decrease the metabolism and subsequently to reduce the energy consumption. The studies available indicate that the lighting condition could be the key of low energy consumption pattern; however, the in situ data are extremely limited. The oxygen consumption rate usually reflects the metabolic rate of organisms. Therefore, in order to explore the effect of in situ lighting conditions on the metabolism of krill, this study measured the oxygen consumption of krill during the successive 11 days under dark and lighting conditions based on the in situ aquarium experiment. In the experiment, the krill was placed in a closed bottle, and the respiration rate of the krill over a period of time was obtained by measuring the difference in the oxygen concentration of the seawater in the bottle before and after the experiment. A robust linear simulation method was used to eliminate the influence of outliers on the trend of daily variation in respiration rate of krill. Results showed that the average weight specific respiration rate of krill under light conditions was (0.270 4 ± 0.074 0) μL · (mg·h) ^-1, and the average weight specific respiration rate under dark conditions was (0.267 3±0.084 0) μL ·mg (·h) ^-1. In this study, in a period close to a natural day, the experimental group of krill was repeatedly tested by changing the conditions of darkness and 100 lx light intensity. The experimental results showed that the oxygen consumption level of krill did not show significant fluctuation. The comparative analysis demonstrated that the oxygen consumption of krill in the winter was significantly lower than that in the summer. The change of lighting condition within a natural day did not impact significantly on oxygen consumption of krill, but the stability of respiration rate of krill was impacted. The study supported the observation that krill was on low metabolism pattern during the winter time, and the stability of such pattern was also proved. The conclusion in the study will provide important basic data for revealing the overwintering mechanism of krill.