Cold comfort for krill? Respiratory consequences of diel vertical migration byMeganyctiphanes norvegicainto deep hypoxic waters

Abstract

Abstract Diurnal vertical migration of krill Meganyctiphanes norvegica into hypoxic waters in the Gullmarsfjord, Sweden would appear to be made possible only by the fact that the deep hypoxic waters are much colder than the surface waters. The ability to regulate O2 uptake over a wide range of PO2s increased dramatically at low temperatures (Pc decreased from 8–11 kPa at 15°C to 4–6 kPa at 7°C) due to a temperature-related decrease in metabolic rate (Q10 > 2). Our experiments examining respiratory regulation and L-lactate accumulation at different O2/ temperature combinations suggest that if the deep waters below the pycnocline had been characterised by the same (high) temperature as found at the surface, then the physiological tolerances or capacities of individuals of this krill population would have been insufficient to permit residence in those waters of more than a few hours.