Algae report number 1, 2026

Abstract

Several stations were not sampled due to bad weather. Phytoplankton species diversity and total cell numbers were high at all stations in the Kattegat. In the Skagerrak, only Släggö was sampled, where lower cell numbers were observed compared with the Kattegat. IFCB images showed low abundances of small cells at Å17, but no microscopy samples could be collected there. The community in the Kattegat was dominated by diatoms, with Pseudo-nitzschia* and Skeletonema marinoi as the most common taxa. Cryptomonads were also common throughout the western sea area. Although cell numbers were lower at Släggö on 7 January, IFCB images indicated that abundances in the Skagerrak were similar to those in the Kattegat when Svea returned one week later, but no microscopy samples were collected then. Integrated chlorophyll concentrations (0–10 m and 0–20 m) were relatively high in the Kattegat but remained within the normal range for the month at all stations.

Diversity and cell abundances of phytoplankton were generally very low in the Baltic Proper. Phytoplankton samples for analysis in the microscope were sampled at four stations; BY15, BY31, BY2 and BY5. In general, it was diatoms of the species Actinocyclus octonarius, small dinoflagellates, Cryptomonads, colony forming cyanobacteria and various ciliates in the Baltic Proper. This is in accordance with images from the IFCB, with the only exception that it was only at BY5 that the filamentous cyanobacterium Aphanizomenon was present in the microscopy sample, while the IFCB found the genus in more or less the entire Baltic. The integrated chlorophyll concentrations were within the normal range for this month at all stations.