Phytoplankton Distribution in the Norwegian Sea in June, 1954, Related to Hydrography and Compared with Primary Production Data

I. Quantitative phytoplankton samples, collected during a cruise in the Norwegian Sea in June, 1954, by the research vessel «G. O. Sars», were worked up by means of the sedimentation metliod. Data on hydrography, primary production, and zooplankton, were supplied by the Research Division of the Fisheries Directorate, Bergen. The survey included stations in Coastal, Atlantic, Arctic, and Polar water. 2. On the basis of the analyses of the phytoplankton communities, eight vegetation areas were recognized. It was demonstrated that the extent of each vegetation area largely depended on hydrographical features. 3. In Norwegian coastal waters, as well as in Atlantic water in the south-eastern part of the Norwegian Sea, the vegetation was relatively poor, and consisted of small-celled diatoms and coccolithophorids. In the central and north-western parts of the Atlantic region an abundant plankton was present, consisting of Rhizosolenia styliformis and several other diatom species of large or medium cell dimensions, as well as of Phaeocystis pouchetii. A narrow zone of mostly Arctic water at the border of the Atlantic water masses supported a vegetation where the presence of Rhizosolenia hebetata f. semispina and associated species was a characteristic feature. In Polar waters in the north-western part of the Norwegian Sea, the plankton was, in general, very sparse, and was composed mostly of smallcelled algae. 4. The size of standing stocks of phytoplankton was expressed as total cell volume (biomass) per litre of sea water. A comparison was undertaken between available data on hydrography, phytoplankton distribution, biomass and primary production. 5. The occurrence of large biomasses was restricted to the central and north-western Atlantic waters. Production in these waters was markedly higher than elsewhere in the Norwegian Sea (Berge 1958). There was evidence that production here was largely or entirely due to those algae which had been recognized in the preserved plankton samples. The relative shares of the various algae in the total production probably varied greatly between localities, but there was some reason to believe that Phaeocystis pouchetii was, on the whole, the most important producer. 6. Using data obtained in the course of the investigation, as well as additional information available in literature, the development of the vegetation in the different parts of the Norwegian Sea during the spring of 1954, was discussed. 7. The spring increase probably started earlier in Coastal, Arctic, and Polar waters, where stability in the uppermost strata was achieved early in 1954, than in Atlantic water where a discontinuity layer, if present, was then located at greater depths. 8. In June 1954, the period of high production had been brought to an end in Coastal, Arctic, and Polar waters, possibly because of nutrient exhaustion in the upper strata. The same was true of southeastern Atlantic water masses, where some degree of stability was likewise apparent. In the central and north-western Atlantic waters, however, a general absence of stratification, in conjunction with favourable light conditions and possibly a moderate degree of turbulent activity, accounted for the fact that the plankton here was apparently still at the stage of spring maximum. 9. The possible origin of the initial stocks of the various species was discussed. There was evidence that many of the species constituting the vegetation in the area of large biomasses and high production, had been introduced into Atlantic water in the southern-most part of the Norwegian Sea early in 1954. The importance of the surface currents in distributing initial stocks was stressed. 10. The investigation amply confirmed the earlier idea (Ramsfjell 1960) that the quantitative as well as the qualitative aspects of the spring development of the phytoplankton in the Norwegian Sea are subject to great variations from one year to another