Algae report number 2, 2025

Abstract

In Kattegat the spring bloom seemed to be just around the corner. Anholt E was sampled in late January with low cell numbers. Only 10 days later, in February, there was an increase in chains of the common spring bloom species Skeletonema
marinoi, but not yet in amounts characteristic of a bloom. The stations in the Skagerrak showed no signs of a spring bloom, as neither the total cell number nor the species composition provided any indication. The integrated chlorophyll concentrations (0–10 m and 0–20 m) were within normal for this month at all stations.

Diversity and cell abundance of phytoplankton were very low in the Baltic Sea, dominated by smaller cells such as Cryptomonadales and smaller Gymnodiniales. The chain-forming diatom Skeletonema marinoi was present at the more northerly
stations. Along the eastern part of Gotland and in the northern parts of the cruise, filaments of Aphanizomenon flosaquae was present according to images from the Imaging Flowcytobot. However, hose samples collected in the same area and analysed under microscope contained no filaments. The integrated chlorophyll concentrations (0–10 m and 0–20 m) were within the normal range for this month at all stations.