Algae report number 9, 2025

Abstract

This report does not include station Anholt E in Kattegat due to hard winds during the cruise. The species diversity was quite high at all stations but the total cell numbers were low in both Kattegat and Skagerrak areas. Diatoms dominated and at the coastal stations, Pseudosolenia calcar-avis dominated. The integrated chlorophyll concentrations (0–10 m) in the Skagerrak and the Kattegat were below normal at all stations. The integrated chlorophyll concentrations (0–20 m) were either in the lower range of normal or below normal.

Species diversity and cell abundances were relatively high in the southern Baltic Sea compared with the other stations during the month, and the plankton community was dominated by diatoms. This was particularly evident at station BY2, where Dactyliosolen fragilissimus and Cerataulina pelagica were more prevalent. In other parts of the Baltic Sea, both species diversity and cell abundances were low, with elevated cell counts observed only among small species. At three stations – BY2, BY29, and BY39 – low occurrences of the filamentous cyanobacterium Aphanizomenon flosaquae were observed. The integrated chlorophyll concentrations (0–10 m and 0–20 m) were within the normal range for the month.