Summary
At Å17 in open Skagerrak, the phytoplankton diversity was high with the potentially fish toxic genus Pseudochattonella*, the diatom Guinardia delicatula and cryptomonadales as the most numerous organisms. At Släggö, the diversity was very low and cryptomonadales and ciliates was found with the highest cell numbers. G. delicatula was the most common diatom and Tripos muelleri the most common dinoflagellate. In the Kattegat the phytoplankton diversity was higher at N14 Falkenberg than at Anholt E, but G. delicatula was numerous at both stations. The potentially toxic dinoflagellate Dinophysis norvegica* was found in elevated cell numbers at N14 Falkenberg. The integrated chlorophyll concentrations (0-10m and 0-20 m) were above normal for this month at Å17, and within normal at all other stations. Diversity and cell abundance of phytoplankton were high at all stations in the Baltic Sea and at the peak of the spring bloom, except at BY5. At BY5, the amount of diatoms were overall low but there were plenty of the dinoflagellates Peridiniella catenata and Gymnodiniales. At the other stations Skeletonema marinoi was more or less dominating, along with Chaetoceros wighamii, several other species of Chaetoceros and other genera. Toxin producing species were in low numbers in the Baltic Sea. The integrated chlorophyll concentrations (0-10m and 0-20 m) were normal for the month at all stations.