Ldh activity in Euphausia mucronata and Calanus chilensis: Implications for vertical migration behaviour

Abstract

Specific lactic dehydrogenase (ldh) activity was measured in Euphausia mucronata and Calanus chilensis. Both key pelagic species inhabit areas of the Humboldt Current System that have permanent subsurface oxygen minimum layer. The specific ldh activity in E. mucronata was two orders of magnitude higher than that of C. chilensis, consistent with E. mucronata's ability to conduct daily vertical migrations through the oxygen minimum layer. In contrast, C. chilensis is restricted to inhabiting oxygenated waters over the oxygen minimum layer without carrying out daily vertical migrations across it. A positive correlation (P < 0.0001) was found between the specific ldh activity and body size in E. mucronata. This study also reports the apparent kinetic properties (Vmax and Km) of ldh and the effect of temperature and pH on the specific activity for both species.