Visual predation by the euphausiid Meganyctiphanes norvegica

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.