Ontogenetic vertical migration of the mesopelagic carnivorous copepod Paraeuchaeta spp. is related to their increase in body mass

Abstract Two dominant mesopelagic carnivorous Paraeuchaeta copepods, Paraeuchaeta glacialis in the western Arctic Ocean and Paraeuchaeta elongata in the western subarctic Pacific, exhibited specialized ontogenetic vertical migration patterns with deeper occurrences of early copepodids (C1) and adults (C6F/M) and shallower occurrences of older copepodids C3−C5. Molt increments in body masses (wet, dry and ash-free dry masses) exhibited highly significant negative correlations with habitat depth. These facts suggest that both Paraeuchaeta species spend their reproductive (C6F/M) and early developmental (C1) stages in deeper layers to avoid predation and migrate upwards to where prey is abundant during the middle-late copepodid stages (C3−C5) to achieve greater mass growth.