Visual predation by the euphausiid Meganyctiphanes norvegica

Abstract

Experiments showed that Meganyctiphanes norvegica are visual predators on copepods. Adult M. norvegica were offered a mixture of equal numbers of late stage Calanus spp. and Metridia longa in total darkness and at a light intensity corresponding to their daytime habitat. Predation rates were 3 times higher in the illuminated containers than in the dark ones (7 vs 2.3 copepods krill-1 18h-1), and higher on M. longa than on Calanus spp. in both light (1.3 times) and darkness (2.3 times). Swimming speeds of M. longa were about 10 times faster than those of Calanus spp., making M. longa more susceptible to mechanical detection.