Routine metabolism of Antarctic krill (Euphausia superba) in South Georgia waters: absence of metabolic compensation at its range edge

Routine respiration rates in the South Georgia stock of Antarctic krill (Euphausia superba) were measured to compare with previously published measurements on stocks from colder locations further south. Within the natural temperature range of this species (-1.8 degrees to 5.5 degrees C), respiration rate data from both the present and previous studies were adequately fitted by a single Arrhenius regression (Q(10) of 2.8), although South Georgia krill showed an upward deviation from this regression between 0 degrees and 2 degrees C (the lower temperature range at South Georgia). Metabolic compensation (i.e. the comparative lowering of respiration rate) at the high temperatures experienced at South Georgia was not apparent, although the higher than predicted metabolic rates at low temperatures suggests acclimation of South Georgia krill to a warm water lifestyle. Weight-specific respiration rate was significantly higher in sub-adults and adults compared to juveniles, highlighting the metabolic burden of reproduction. South Georgia krill showed no further increase in respiration rate when exposed to acute temperatures (5.5-12.2 degrees C), indicating that they were already at the limit of aerobic capacity by 5.5 degrees C. Overall, this study shows that even small degrees of additional warming to South Georgia waters are likely to make conditions there metabolically unsustainable for Antarctic krill.