MEGANYCTIPHANES-NORVEGICA (M-SARS) (EUPHAUSIACEA) A VORACIOUS PREDATOR ON CALANUS, OTHER COPEPODS, AND CTENOPHORES, IN OSLOFJORDEN, SOUTHERN NORWAY

In zooplankton samples collected by means of vertical Nansen net hauls for the purpose of studying long-term changes in Oslofjorden, many injured specimens of Calanus were found. These had exactly the same appearance as some Calanus that were found in Meganyctiphanes 'baskets'. It is concluded that feeding activity of Meganyctiphanes was the cause for the occurrence in the samples of injured Calanus and other copepods, which had evidently been discarded or lost by the predators while in the net or immediately in front of it. Calanus was the main food of Meganyctiphanes in the area at that time followed by smaller copepods. Specimens that had been attacked by Meganyctiphanes constituted a significant percentage of the total number of copepods. These important relationships would not have been disclosed by examination of Meganyctiphanes stomachs alone. It is hoped that the photographs presented in this paper will prove useful to other planktologists working in waters with numerous Meganyctiphanes. With regard to fisheries biology, an overall beneficial effect of an abundant Meganyctiphanes population is not obvious since the Meganyctiphanes may consume more potential fish food than they produce. By eating Pleurobrachia, however, Meganyctiphanes may also save copepods and fish larvae from being eaten by those.