GRAVIPERCEPTION AND MOTILITY OF 3 PROROCENTRUM STRAINS IMPAIRED BY SOLAR AND ARTIFICIAL ULTRAVIOLET-RADIATION

The effects of solar and artificial ultraviolet radiation on the motil ity and graviorientation of three strains of the dinoflagellate Proroc entrum were studied. P. micans isolated from the Baltic Sea shows a pr onounced negative gravitaxis which switches to a positive one even aft er short exposure times to either solar or artificial UV irradiation. In constrast P. minimum strains isolated from the Kattegat and the Atl antic coast off Portugal showed only a weak upward orientation. In all three strains the linear swimming velocity decreases after short expo sure times and, in addition, the percentage of motile cells in the pop ulations drastically decreases. Removing the ultraviolet component of solar radiation with a cut-off filter prolongs the tolerated exposure times.