Vertical distribution and trophic interactions of zooplankton and fish in Masfjorden, Norway

Abstract

The distribution, biomass, and predator-prey relationships of the pelagic assemblage in Masfjorden, western Norway, was studied in January 1989. The pelagic biomass was dominated by particulate organic matter. Biomasses of copepods, macroplankton, and mesopelagic fishes were of the same order of magnitude, while the biomass of larger pelagic fishes were one order less. Predator-prey relationships seemed most important at intermediate and higher trophic levels. Two sound-scattering layers, consisting of adult Maurolicus muelleri (lower layer) and juvenile M. muelleri (upper layer) performed instantaneous lightdependent vertical migration. Vertical distributions are explained in terms of balancing food demands against predation risk.