The influence of water exchange on zooplankton dynamics and species development in a south Norwegian fjord

During experiments in a south Norwegian fjord in March and April1979, distribution and development of zooplankton were investigatedin detail. Numbers of protozooplankton, meroplankton and holoplanktonwere determined as individual species. Strong water exchangecaused a high variability in plankton composition and biomass.Changes in salinity and temperature as well as numbers of planktonindividuals and in the percentage composition of the developmentalstages of the spring spawning Calanus finmarchicus revealedthat a wind-induced inflow of Skagerrak water along the southwestNorwegian coast also entered the Rosfjord. In contrast to theAtlantic water with low numbers of copepods from the hibernatinggeneration, in the Skagerrak water the spring generation ofC.finmarchicus had already developed up to the first and secondcopepodite stages. The Skagerrak water was already very richin phyto- and zooplankton organisms. Here, an increase in biomassover time mainly resulted from the development of younger toolder copepodite stages and from a considerable increase innumbers of the tintinnid, Leprotintinnus pellucidus. The verticaldistribution of plankton organisms and fecal pellets was closelyassociated with the occurrence and the stratification of watermasses coming into the Rosfjord.