Phytoplankton observations in offshore Norwegian coastal waters between 62° N and 69° N. 2. Diatom societies from Möre to Vesterålen, March–April 1968–1971
Phytoplankton data obtained by the Utermohl technique were analysed for a description of diatom, societies. Near-coastal, intermediate coastal, semiatlantic, and atlantic waters were considered separately. Regional variation was most evident in the near-coastal and intermediate coastal categories, especially a definite change from a Skeletonema society in the south to a 'Mixed spring diatom society' in the north. Changes from year to year were most notable in the atlantic and semiatlantic water-masses, 1970 being outstanding by the predominance of a Chaetoceros-Tha- lassiosira nordenskioeldii society with a very subordinate Skeletonema component, from Tröndelag to the northernmost part of the area. The introduction in 1927 of an allochthonous Asterionella glacialis society in the whole Möre area, recorded by Gran, and the occurence of the 1970 vegetation in atlantic waters during the present survey, are taken as illustrations of long-distance transport from the northern North Sea area to Möre, Tröndelag, and even to the coast of Vesterålen. The special situation on Haltenbanken is discussed and the seasonal pattern of the vegetation in the adantic waters is considered.