Potential grazing, respiration and growth of Euphausia distinguenda in relation to the oxygen minimum zone at the Eastern Tropic

Abstract

Euphausiids play an important role in the carbon cycling of pelagic ecosystems. They perform diel vertical migrations promoting a transport of organic matter from the euphotic zone to deep layers. The oxygen minimum zone (OMZ) in tropical oceans affects to the diversity, distribution and physiological processes of marine organisms. In order to study the relationship between the physiological processes of Euphausia distinguenda and the OMZ, we collected samples of euphausiids in the Eastern Tropical Pa- cific off Mexico (ETPM) during November 2009. We assessed the indices of potential grazing (specific gut fluorescence, GF), respiration (specific electron transport system activity, ETS) and growth (specific aminoacyl-tRNA synthetases activity, AARS) and the individual protein content. E. distinguenda behavior was characterized a diel vertical migration descending during the day and ascending to the surface at night. Specific ETS and AARS activities showed the same daily pattern; where high metabolic activities were found during the night in superficial highly oxygenated waters. Both growth and respiration rates were significantly reduced within the OMZ. However, specific GF had not daily variations and it is suggested that E. distinguenda migratory behavior into the OMZ is not a feeding response but a strategy to avoid predation.