Algae report number 7, 2022

Type: Report
Author: Marie Johansen


The analyses were made onboard the ship R/V Svea during the cruise. Water from integrated samples or discrete depths were filtrated down to filters with 5μm pore size. The method is more suitable for identifying larger and more robust cells whereas smaller cells or fragile cells are difficult to determine taxonomically and missed to a higher degree.
The diatom Proboscia alata was found in high concentrations in the integrated hose samples taken at all stations in the Skagerrak and the Kattegat. Among the smaller cells numerous cells of Emiliania huxleyi were present. The species diversity was overall low. Several smaller chlorophyll fluorescence maxima were found at several depths. Stations at the transect Å-snittet presented a fluorescens maximum at 10-12 meter and closer to the coast Dinophysis acuta dominated the samples.
No clear surface accumulations of cyanobacteria were found in the Baltic Sea during this expedition. This was probably due to high wind speed and waves that mixed the water. The samples from the southwest stations showed only few filaments in the water. At the middle of the southern part outside Bornholm a few more filaments were found in both the surface
sample and the integrated sample. At the southeastern part, the water was well mixed with relatively high fluorescence down to 20 meters. Here, both Aphanizomenon flosaquae and Nodularia spumigena* were  common in both surface and hose samples. The eastern middle part of the Baltic Proper had a little more filament at BY15 Gotland Deep here small surface accumulations were also noted from the skip a bit north of the station. At the northernmost part of the expedition, north of Gotland, slightly larger amounts of filaments were found. At both stations it was mixed down to about 12-15 meters due to wind. If the wind calms down, surface accumulations can form quickly. In this area, satellite images have also indicated surface accumulations in recent days. At BY38 between Öland and Gotland, the wind had calmed down a bit and the waves were smaller. Here, small grains were seen in the water, which could be small aggregations of filaments and lead to surface accumulations if the wind decreases. The surface sample appeared to have more filaments than the hose sample, indicating that the filaments may be on their way to the surface. In the western parts, a lot of cyanobacterial filaments were found, but mostly it was the genus Dolichospermum that dominated.