Blooms ofGyrodinium aureolum(Dinophygeae) in North European waters, accompanied by mortality in marine organisms

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Abstract
Mass occurrence of the dinoflagellate Gyrodinium aureolum Hulburt in coastal waters on the Norwegian south-west coast in the autumn 1976 was accompanied by fish mortality in floating net cages and by mortality in various littoral organisms. Cell concentrations above 20 million cells per litre were recorded in coffee-brown patches in sheltered localities. The hydrographical and meteorological records indicate that the bloom started after a wind-conditioned upwelling, and proceeded in water masses affected by heavy freshwater runoff. The morphology and taxonomy of G. aureolum is discussed, and a synopsis is presented of the occurrence of this species which is among the most common bloom dinoflagellates in European waters. Mortality in various marine organisms during blooms of G. aureolum is discussed; especially the possibility of oxygen deficiency associated with the blooms is considered.