Seasonal changes in the phytoplankton at various points off the Norwegian West Coast : (Observations at the permanent oceanographic stations, 1945-46)

Abstract

1. Quantitative phytoplankton samples from four of the Permanent Oceanographic Stations of the Institute of Marine Research of the Fisheries Directorate, Bergen: Utsira and Sognesjøen in the southern part of the Norwegian west coast and Skrova and Eggum in the northern part, covering all seasons of the year, were examined by the sedimentation method. The results were correlated with hydrographic data, supplied by Dr. JENS EGGVIN. 2. The main features of the annual phytoplankton cycle at these points of the outer coastal region are described. Common are the winter poverty and the spring increase, which occurred about three weeks earlier at the southern stations than at the northern ones. During the remainder of the year: late spring, summer and autumn, the seasonal changes were notably different at all four localities. Essential annual changes at the same locality were also observed. 3. Factors of general nature: the different light supply due to geographical position and the delayed vernal stabilization at the northern stations, conditioned by a smaller fresh-water supply, were pointed out as main factors causing the delay in spring phytoplankton growth in the north. Extensive winter mixing, inducing a more pronounced dilution of the winter population in the north, may also result in smaller phytoplankton stocks in early spring. 4. The difference in the changes taking place after the spring increase were tentatively tracecl back to hydrographical factors. The impression was gained that, at this time of the year, the outer coastal waters constitute a mosaic of vegetation areas, conditioned by the variation in the degree of stabilization and by the local admixture of adjoining water masses, the fjord waters to the east and offshore waters to the west. At the Eggum station the effect of local hydrographical conditions seemed to be very pronounced. 5. The composition of the populations was described in some detail. The occurrence of large populations of Euglenaceae in May-June at the northern stations is a noteworthy feature. 6. No detailed analysis of the ecological factors which are at play has been feasible, but the ecological situation at the various seasons was discussed. 7. A brief review of the present situation in phytoplankton research of Norwegian coastal waters was presented, especially in view of its application to fisheries problems.