MEPS 228:193-204 (2002)  -  doi:10.3354/meps228193

Is the omnivorous krill Meganyctiphanes norvegica primarily a selectively feeding carnivore?

Stein Kaartvedt*, Tom Larsen, Knut Hjelmseth, Maren S. R. Onsrud

Department of Biology, University of Oslo, PO Box 1064 Blindern, 0316 Oslo, Norway

ABSTRACT: Feeding of the krill Meganyctiphanes norvegica was studied at a 120 m and a 200 m deep site in the Oslofjord, Norway. Converting stomach content of copepod mandibles and gut fluorescence into carbon equivalents suggested that the highest carbon gain was from carnivorous feeding, although contribution from herbivorous feeding was of the same order of magnitude in spring. High daytime gut fluorescence during spring suggested that sedimenting algae were efficiently cropped in deep water. On other occasions algae were exploited during nocturnal vertical migrations. In late summer, M. norvegica acted as a selectively feeding carnivore, primarily preying on Temora longicornis during nocturnal migrations to upper layers. Algal food was neglected at this time. During winter, the feeding conditions differed between the 2 stations. Estimated carbon equivalents of the stomach content were high at the shallowest site, and low at the deepest site. We ascribe this difference to the ability of M. norvegica to visually detect and exploit overwintering Calanus spp. during daytime at the 120 m station, while Calanus spp. overwintered below the daytime depth of M. norvegica at the 200 m deep station. Cyclopoid copepods were normally under-represented in the stomach contents.

KEY WORDS: Temora · Calanus · Visual feeding · Gut fluorescence · Diel vertical migration

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