| Summary: | This thesis investigates mesozooplankton abundance, composition and distribution in Svalbard waters in relation to hydrography. Sampling was carried out in the archipelago of Svalbard mainly during summer and autumn between 2000 and 2004. From cluster analysis four species assemblages were distinguished and these reflected differences in hydrography and bottom depth. In particular the distribution of the Atlantic Calanus finmarchicus relative to that of the Arctic Calanus glacialis was associated with different hydrographic regimes. Differences in the species assemblages primarily resulted from variations in species densities rather than from taxonomical variation. For species of Atlantic and Arctic origin significant relationships with temperature and salinity were found. Regression models were used to quantify the influence of water mass characteristics on the abundance of the three different Calanus species that co-occur in the study area. About 50% of the variability in abundance of each Calanus species could be accounted for by variability in temperature and salinity. C. finmarchicus abundance was positively related to warmer and more saline waters, as expected from its distributional southern core area. Conversely, the Arctic species C. hyperboreus was more abundant in colder and fresher waters. The numbers of C. glacialis decreased with increasing temperature and salinity in shallow areas, while the opposite trend was found in deep locations. Salinity and temperature between 50 - 150 m depth were in most cases better predictors for Calanus spp. abundance than near-surface conditions. Variability in the vertical distribution of the three Calanus species and Metridia longa reflected life history and behavioural adaptations on diel and seasonal scale. Diel vertical migration was observed for copepodite stages of M. longa but generally not for Calanus spp. The copepodite stage composition indicated a south to north delay in the succession of Calanus development and that the descent to overwintering depth had ...
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