Algae report number 2, 2026

Abstract

The spring bloom was observed at all stations this month. The diatom Skeletonema marinoi dominated at all stations, but in Skagerrak other diatoms were also relatively common, whereas in Kattegat S. marinoi had a more prominent dominance. Dinoflagellates were overall few. Images from the IFCB (Imaging Flow CytoBot) onboard the R/V Svea showed that the spring bloom was ongoing until the entrance to the Sound where cell numbers decreased rapidly. Integrated chlorophyll concentrations (0–10 m and 0–20 m) were high and well above what is normal range for the month at all stations along the Swedish west coast all the way to the Sound.

Diversity and cell abundances of phytoplankton were generally very low, but normal for the season, in the Baltic Proper. In general, there were diatoms of the species S. marinoi, small dinoflagellates, Cryptomonads and the ciliate Mesodinium rubrum that were found in the Baltic Proper. This is in accordance with images from the IFCB, where also the difference in number of captured images between the west coast and Baltic was obvious. The integrated chlorophyll concentrations were within the normal range for this month at all stations.