Mass occurrence of Gyrodinium aureolum Hulburt and fish mortality along the southern coast of Norway in September-October 1981

Abstract

At the end of September 1981 the sea appeared "coffee brown" along the southern coast of Norway due to mass occurrence of Gyrodinium aureolum Hulburt. The maximum cell concentration observed was 70*10^6 cells*1^-1. When most abundant, the algae formed a more or less continuous, brownish belt from the Oslofjord to the Flekkefjord area, extending up to 30 km off the coast, From all along the coast fish mortality associated with brown water was reported. The mortality was mainly among fish kept in nets and cages, but dead wild fish and invertebrates were also observed. Measurements of oxygen and light microscopy on gills from moribund fish indicated that neither lack of oxygen nor physical clogging of the gills caused the mortality.