Økologiske undersøkelser nær iskanten i Barentshavet somrene 1979 og 1980

During the summers of l979 and 1980, ecological investigations were carried out in the marginal ice zone in the Barents Sea. In the investigation an attempt is made to follow the development of the production processes, from nutrients via phytoplankton and zooplankton to capelin, in order to map the feeding conditions for the capelin and its variations. The methods used in the field work and most of the results obtained during the two summer seasons are presented by ELLERTSEN -et -al. (1981). In the present report we discuss and summarize the field results so far and compare them with the results from a model. The results show a close relationship between ice melting and recession and a phytoplankton bloom occurring at the ice edge. It seems that the decrease in salinity in the upper few meters due to ice melting produce a sharp increase in water stability. Thereby favourable conditions are created for an intense phytoplankton bloom. This bloom seems to occur somewhat earlier than the spring bloom in the areas of the Barents Sea not covered by ice, where water stability is mainly influenced by the warming of the upper layers. Zooplankton development follows very close that of the phytoplankton, with a bloom starting near the ice edge. The biomass was found to increase with the distance from the edge. This tendency is most clear in the upper layers, where the zooplankton spawning and the development of the zooplankton larvae occur. The main bulk of the zooplankton consisted of the copepod Calanus finmarchicus. The most numerous species was the small copepod Oithona similis. There was a change in age composition of -C. finmarchicus with the distance from the ice, the nauplii and the younger copepodite stages predominating in the north. The younger stages (I-III) were most abundant in the surface layer where they had hatched earlier in the year, while the older stages (IV-V and adult females) had overwintered and predominated in the deeper layer. The stomach contents of 12-18 cm capelin from several stations were investigated. The stomach filling seemed to be related to the plankton density in the sea, with highest filling in areas with much plankton. The species composition in the stomachs roughly corresponded with the plankton composition, with a tendency to a higher numeric percentage of euphausiids and chaetognaths in the stomachs than in the plankton. Near half of the contents, as weight, consisted of calanoid copepods, while the euphausiids, chaetognaths and amphipods made up 30, 10 and 6 per cent of the weight respectively. A model describing the growth of phytoplankton and zooplankton along a north-south section in the Barents Sea is also briefly described. Using ice map data obtained via satellite, several simulation runs have been performed. The dynamics of the phytoplankton growth seems to agree with what we believe it should according to the available data. However, some discrepancies indicate areas that should be further investigated in order to increase our knowledge and improve the model. The zooplankton part of the model produces results that are more questionable. Variations in zooplankton biomass are reasonably calculated whereas the stage distribution does not fit our data. Reasons for this are discussed