Summary
Extraordinarily high levels of chlorophyll a and high cell numbers were found in the Skagerrak and Kattegat areas in mid January. The diatoms Skeletonema costatum, Pseudo-nitzschia delicatissima-group and Thalassiosira nordenskioeldii dominated the phytoplankton samples. P. delicatissima-group was found with cell numbers above its critical limit, although there has been no reports of AST (Amnesic Shellfish Toxin) in Swedish waters, which is a toxin potentially produced by this group of algae. In the Baltic Sea the number of species and the cell numbers were low causing low chlorophyll a values normal for the season.