Offshore growth OfGyrodinium aureolum(Dinophyceae) - The cause of coastal blooms in the Skagerrak area?

Abstract

In the autumns of 1982 and 1983 a close connection was found between the occurrence of water of high salinity (> 27 ‰) and the dinoflagellate Gyrodiniurn aureolum HULBURT. These observations were made in Gullmarsfjorden situated on the Swedish west coast. It appeared that the increase in salinity was not due to local upwelling of deep water, but was caused by inflows of surface water from the Skagerrak. In 1983 this was confirmed by sampling in the Skagerrak, where the dinoflagellate was found one week before it was observed in the fjord. Upwelling is believed to play an important role in the development of blooms of G. aureolum along the Norwegian coast. It seems equally possible, however, that the blooms result from offshore growth and landward transport by wind-induced currents. The large amounts of algae observed on some occasions in coastal waters would then be the result of concentrative processes such as convergent flows, in connection with the positive phototaxis of G. aureolum. In this connection some observations suggest that the salinity front between the Baltic-Norwegian Coastal Current and the Skagerrak water is important.