Effect of freshwater discharge, intrusions of coastal water, and bathymetry on zooplankton distribution in a Norwegian fjord system

Freshwater discharge from a hydroelectric power plant had astrong impact on plankton transport and distribution withinthe fjord system. Most zooplankters submerged beneath the outgoingbrackish current, and subsequent advection by the compensationcurrent caused high concentrations near the power plant outlet.Currents driven by wind-induced changes in the density fieldin the adjacent coastal waters dominated transport between thefjord system and Outer regions. Normal plankton advection ratesappeared to be on the same order of magnitude as local zooplanktongrowth within the fairly enclosed system. However, during strong,short-term intrusions of coastal water, plankton compositionand distribution changed markedly in the course of a few days.The bathymetry seemed to be decisive for the distribution ofAcartia, which was recurrently found in highest numbers at theshallowest sampling location.