Summary
All stations along the Swedish west coast had quite high total cell numbers except Å17 that had very low total cell numbers All stations had moderate to high biodiversity. Diatoms were generally the most abundant group across sites, particularly Pseudosolenia calcar-avis and Cerataulina pelagica. The coccolithophore Emiliania huxleyi was consistently present. Dinoflagellate presence was low across all locations, with only a few species noted. The integrated chlorophyll concentrations were within normal for this month. All stations in the Baltic Sea during this sampling period exhibited low to moderate species diversity, with generally high cell abundances observed. The diatom Dactyliosolen fragilissimus was common at several stations, particularly at BY38 and in the eastern Baltic Sea, contributing to high cell counts despite low overall species diversity. Cerataulina pelagica was prominent in the southern stations, notably dominating the community at BY5 (Bornholm Deep). Chlorophyll concentrations were above normal at multiple stations in the southern and eastern Baltic Sea. However, of these stations, only BY2 samples were examined using the microscope. Plankton images from the Imaging Flow Cytobot (IFCB) onboard R/V Svea confirmed that C. pelagica was blooming at the stations with elevated chlorophyll concentrations in the southern Baltic Sea, and that D. fragilissimus was the main contributor to the high chlorophyll levels in the eastern Baltic Sea. Ciliates and small taxa such as cryptomonadales and gymnodiniales were consistently present across stations, adding to the diversity. The integrated chlorophyll levels (0–10 m) were above normal at BY1, BY2, BY4, and Hanö Bight, as well as at BY10 and BY20.