ORIGINAL RESEARCH article
Front. Mar. Sci.
Sec. Marine Ecosystem Ecology
This article is part of the Research TopicWaters of the Baltic Sea Region: Past, Present, and Future Perspectives on Aquatic HabitatsView all articles
Diverging temporal trends and environmental drivers of dominant cyanobacteria in the Gulf of Riga, 1976–2024
Provisionally accepted
- 1Latvian Institute of Aquatic Ecology, Riga, Latvia
- 2Latvian Environment, Geology and Meteorology Center, Riga, Latvia
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Cyanobacteria are major contributors to summer primary production in the Baltic Sea, where extensive blooms of diazotrophic taxa such as Aphanizomenon flosaquae and Nodularia spumigena shape ecosystem functioning. However, the environmental drivers regulating their biomass dynamics remain incompletely understood. Using long-term monitoring data (1993–2024) from the Gulf of Riga, this study examined how nutrient concentrations, salinity and river runoff influenced cyanobacterial bloom composition and intensity. While both taxa co-occurred, A. flosaquae contributed substantially more biomass, allowing for a detailed statistical analysis. GAM (Generalized Additive Model) revealed that winter dissolved inorganic phosphorus (DIP) was the strongest and most consistent predictor of subsequent summer biomass, suggesting a 'legacy effect' where early-season nutrient availability governs bloom magnitude months later. Summer dissolved inorganic nitrogen (DIN) also contributed significantly, which is consistent with the A. flosaquae ability to meet nitrogen requirements through N-fixation. In contrast, integrated salinity and winter river runoff exhibited limited effect, although co-plot analyses indicated that higher-salinity regions, naturally poorer in DIP, amplified the role of phosphorus in shaping biomass responses. Understanding how these factors interact is essential for predicting bloom development in the Baltic Sea.
Keywords: Aphanizomenon flosaqae, Nodularia spumigena, Baltic Sea, Gulf of Riga, GAM, Long-term data
Received: 26 Sep 2025; Accepted: 15 Dec 2025.
Copyright: © 2025 Liepiņa-Leimane, Jurgensone, Barda, Kokorīte and Aigars. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence: Ineta Liepiņa-Leimane
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