Dr. Heta Rousi from University of Turku, Finland, will talk about her current scientific work.
Online via Zoom on Monday 5 October 2026
15:00 cet (Rostock, Stockholm time zone);
16:00 eet (Helsinki, Tallinn time zone)
Please register via the link at the bottom (just name and e-mail address) to get the participation link.
Effects of winter NAO and water physical and chemical parameters on cyanobacteria biomass in the Northern Baltic Sea
Abstract:
Cyanobacteria blooms are a serious problem in the coastal waters of the Archipelago Sea and Gulf of Finland. Many species of cyanobacteria are benefitting from the climate change as warmer water temperatures, including marine heatwaves, act in their favor. In addition, many of the species in the Northern Baltic Sea proliferate in low salinity conditions. However, cyanobacteria are taxonomically rich and the communities consist of several physiologically and functionally differing species, which have varying environmental optima.
Most attention is naturally given to the conspicuous, filamentous surface bloom forming cyanobacteria, including the potentially toxic Nodularia spumigena and Dolichospermum spp. as well as Aphanizomenon spp., while not so much is known about the environmental preferences of single-celled, non-diazotrophic taxa such as Romeria spp. or Snowella spp. Using long-term monitoring data and generalized linear mixed models, our aim was to investigate the proliferation of the Archipelago Sea cyanobacteria community between 1991 and 2023 as a result of physical and chemical variables, including NAO of the previous winter, wind conditions, surface water temperature, salinity and pH as well as free phosphate and ammonium in the surface water.
Our results indicate clear differences in the environmental requirements between diazotrophic and non-diazotrophic species. For instance, the biomasses of diazotrophic cyanobacteria seem to be higher after colder winters with less positive winter NAO and vice versa regarding the non-diazotrophic taxa. A direct reason for this remains unclear, but it may be related to the terrestrial nutrient loads after colder vs. warmer winters. Diazotrophic species do not require nitrogen in the sea, because they are able to fix airborne N2 and transform it to ammonia. In addition, most cyanobacteria species are efficient in phosphate storage, through luxury uptake, where cells absorb phosphorus far in excess of their immediate growth requirements when it is abundant in the environment. Consequently, these intracellular nutrient dynamics uncouple cyanobacterial proliferation from ambient nutrient concentrations, complicating the response between bloom development and measured environmental nitrogen and phosphorus levels.
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