Layout 1 Impact of cyanobacterial blooms on water resources and animal and human health The development of toxigenic cyanobacteria represents one of the main problems for the multiple uses of water, also consti- tuting a risk for the health of people and animals (Meriluoto et al., 2017a, 2017b; Chorus & Welker, 2021). In addition to the problems connected with the production of odorous compounds (Akcaalan et al., 2022; Manganelli et al., 2023), the presence of cyanobacterial proliferation has important negative conse- quences for the use of aquatic resources, due to the production of a wide range of toxic molecules (cyanotoxins) in waters in- tended for drinking and recreational use (Chorus et al., 2021). Cyanotoxins are produced by a wide variety of cyanobacte- rial species. The most important classes of cyanotoxins include microcystins and nodularins (hepatotoxic), cylindrospermopsins (cytotoxic), anatoxins and saxitoxins (neurotoxic). The abun- dance of toxins synthesized during a cyanobacterial bloom is not directly linked to biomass but depends on several factors, such as the species involved in the blooms and the proportion of toxic strains within the cyanobacterial population. In addition to species capable of producing one or more classes of toxic compounds, there are other species for which the production of toxins has yet to be proven. The impact of cyanotoxins on human health can be severe, ranging from skin rash to illness and, rarely, death. Exemplifying cases include deaths caused by microcystin-contaminated water used for hemodialysis in Caruaru (Brazil) (Azevedo et al., 2002) and several illness cases (gastrointestinal and skin reaction, asth- matic symptoms, and swelling) documented worldwide con- nected with the contamination of drinking and bathing waters by cyanobacteria (Metcalf & Codd, 2012; Wood, 2016). Despite the intrinsic difficulties in epidemiological investigations due to the presence of confounding factors, a number of studies have also highlighted a possible association between the incidence of cancer cases in humans and the presence of cyanotoxins in water intended for human consumption (Svirčev et al., 2017). Several other cases of lethal intoxication of animals caused by the con- SPECIAL SECTION Potentially toxic cyanobacteria blooms in the Southern Alps and the Italian peninsula Development of cyanobacterial blooms in Italy: towards an integration of scientific research and baseline monitoring Nico Salmaso,1,2 Leonardo Cerasino1 1Research and Innovation Centre, Fondazione Edmund Mach, San Michele all’Adige; 2National Biodiversity Future Center (NBFC), Palermo, Italy ABSTRACT This paper introduces and summarises a selection of contributions that were presented during a workshop on cyanobacterial blooms held at S. Michele all’Adige (Trento) in December 2023. The meeting originated with an increasing interest in a reciprocal exchange of knowledge and experiences between government bodies and research institutions following the widespread cyanobacterial blooms detected in the southern Alpine area and other Italian regions. The papers have been collected in the special issue “Potentially toxic cyanobacteria blooms in the southern Alps and the Italian peninsula”.Corresponding author: Nico Salmaso, Research and Innovation Centre, Fondazione Edmund Mach, via E. Mach 1, 38098 San Michele all’Adige, Italy. E-mail: nico.salmaso@fmach.it Key words: cyanobacteria, toxic cyanobacteria, review, Italy, mon- itoring. Authors’ contributions: all the authors made a substantive intellec- tual contribution. All the authors have read and approved the final version of the manuscript and agreed to be held accountable for all aspects of the work. Conflict of interest: the authors declare no potential conflict of in- terest. Funding: none. Availability of data and materials: all data generated or analyzed during this study are included in this published article. Acknowledgements: we would like to thank all the authors who invested their time in preparing the papers submitted for this spe- cial issue. Special thanks to the reviewers who helped to improve the manuscripts. We acknowledge the institutional support of Fon- dazione Edmund Mach and its commitment to recognizing the rel- evance of this topic, as well as its support in organizing the Workshop on toxigenic cyanobacteria held in S. Michele all’Adige in December 2023. In particular, we extend our gratitude to Lisa Rizzetto and Alessandro Gretter for their coordination. We also thank Floriana Marin and the Office for Communication and Ex- ternal Relations for their valuable contribution. Received: 19 March 2025. Accepted: 25 March 2025. Publisher’s note: all claims expressed in this article are solely those of the authors and do not necessarily represent those of their affil- iated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher. ©Copyright: the Author(s), 2025 Licensee PAGEPress, Italy Advances in Oceanography and Limnology, 2025; 16:13834 DOI: 10.4081/aiol.2025.13834 This work is licensed under a Creative Commons Attribution- NonCommercial 4.0 International License (CC BY-NC 4.0). Development of cyanobacterial blooms in Italy: towards an integration of scientific research and baseline monitoring 23 sumption of water contaminated by toxic cyanobacteria were documented worldwide (Metcalf & Codd, 2012; Fastner et al., 2018). Evidence has also been produced on the accumulation of microcystins along the food chain, including fish (Banerjee et al., 2021; Falfushynska et al., 2023). Effects of blooms can have a serious economic impact on tourism (Hamilton et al., 2014) and the exploitation of water for drinking purposes, as in the well-known “water crisis” that impacted the city of Toledo (Ohio), caused by a massive toxic bloom of Microcystis aerug- inosa (Kützing) Kützing that led to the closure of the aqueducts for weeks due to contamination of lake water by microcystins (Steffen et al., 2017). Documentation of water blooms in Italy Cyanobacterial growth and blooms are promoted by eu- trophication and increasing water temperatures. The increase in algal nutrient loads (phosphorus and nitrogen compounds) dis- charged into water bodies is the main controlling factor of eu- trophication (OECD, 1982; Istvánovics, 2009). Global warming creates favorable conditions for the growth of cyanobacteria both directly and indirectly by increasing water temperatures and stability of the water column (Paerl & Paul, 2012). Eutroph- ication and climate change act in synergy, reinforcing each other (Moss et al., 2011; Fastner et al., 2016; Hamilton et al., 2016), and causing an expansion of favorable conditions for the devel- opment of blooms (Hou et al., 2022) and production of cyan- otoxins (Mantzouki et al., 2018b, 2018a). The dynamics of cyanobacterial blooms can be highly vari- able, ranging from localized and episodic events lasting a few hours or days to persistent accumulations of biomass over large areas lasting several days or weeks (Steffen et al., 2017). Glob- ally, a significant increase in the occurrence of blooms caused by cyanobacteria has been observed, attributed to the effects of global warming, which for several decades has been causing a systematic increase in water temperatures and, consequently, an increase in thermal stability, which is essential for the initiation and maintenance of blooms over time (Huisman et al., 2018; Hou et al., 2022). In the last two decades, the increase in the occurrence of algal blooms has also been documented in the Alpine region south of the Alps, and in several other Italian regions (Man- ganelli et al., 2014). Lake water warming was included among the most important factors promoting cyanobacterial develop- ment in the Alpine region (Gallina et al., 2013; Salmaso et al., 2018, 2024; Fenocchi et al., 2025) and, in general, in Italian lakes (Funari et al., 2014; Pareeth et al., 2017; Ludovisi et al., 2021). On the other side, the documentation of the frequency of episodes was improved after the engagement in 2008 of Re- gional Environmental Protection Agencies (ARPAs) in the mon- itoring of algal blooms in marine and freshwater environments. Since then, the monitoring of cyanobacteria by ARPAs gener- ated a wealth of information, which, most of the time, has been used exclusively to comply with legislation on the surveillance of water bodies for recreational and drinking purposes on a re- gional basis. In this regard, these observations represent an in- valuable source of knowledge complementing the scientific investigation, which, with the exclusion of the systematic studies carried out under the umbrella of the Long-Term Ecological Re- search networks (Morabito et al., 2018; Capotondi et al., 2021), are more focused on specific objectives, with time constraints linked to the life of the projects. In order to promote a better exchange of information and experience, several local environmental and health authorities and research institutes involved in the monitoring and study of cyanobacteria participated in a meeting organized at S. Michele all’Adige in December 2023, with the aim of creating a common framework for the mutual exchange of information and discus- sion on the causes and solutions to mitigate the effects of cyanobacterial blooms. In addition to this introductory paper, this special issue, en- titled “Potentially toxic cyanobacteria blooms in the southern Alps and the Italian peninsula”, includes a selection of papers published by the participants of the meeting. Although the re- gional scale in the contributions was mostly limited to the North- ern Italian regions, most of the results were also discussed and interpreted taking into account the Italian context. A few papers were focused on the documentation of the dis- tribution of cyanobacterial blooms at the southern border of the Alps, specifically in the Po River basin and the eastern Alps (Buzzi et al., 2025), in the Trentino Province (Pozzi et al., 2024) and Lake Garda (Zampieri et al., 2024). Overall, these three con- tributions demonstrated the existence of a high number of bloom events across the regions investigated by the environmental agencies, with a highly diversified number of cyanobacterial species, most of them potentially toxigenic, and therefore re- quiring great attention in their development and risk assessment (among others, M. aeruginosa, Aphanizomenon flos-aquae Ralfs ex Bornet & Flahault, Planktothrix rubescens (De Candolle ex Gomont) Anagnostidis & Komárek, Dolichospermum circinale (Rabenhorst ex Bornet & Flahault) Wacklin, Hoffmann & Komárek, and D. lemmermannii (Richter) P.Wacklin, L.Hoff- mann & J.Komárek). In most cases, blooms were associated with the presence of microcystins in the environmental samples, even if no specific analyses were performed on the isolates to clearly identify the producers. These works highlighted the ne- cessity to integrate into the baseline monitoring new technolog- ical approaches to monitor real-time episodes characterized by sudden appearance and variable persistence, and to study the taxonomic and functional characteristics of blooming species by molecular and analytical methods (Buzzi et al., 2025). These el- ements are essential considering that the activity by ARPAs al- lows more timely surveillance and analysis of cyanobacteria in the event of blooms, enabling rapid communication with public authorities and implementation of recovery plans (Pozzi et al., 2024; Zampieri et al., 2024). The new occurrence of populations of Raphidiopsis raci- borskii (Wołoszyńska) Aguilera & al. in small eutrophic lakes in Lombardy and Veneto was the object of the work by Austoni et al. (2025). The formation of blooms and discoloration of R. raciborskii in small artificial lakes and narrow canals in Emilia Romagna were described by Del Pasqua et al. (2024a). An im- portant potential problem connected with the correct identifica- tion of the nature of water discolorations in water bodies was addressed by Del Pasqua et al. (2024b). These authors reported several interesting case studies including the occurrence of co- existing red and green blooms of Euglena sanguinea Ehrenberg Nico Salmaso and Leonardo Cerasino24 and Oscillatoria sp. in the same water body, and several purple and orange colorations caused by massive surface development of sulphur bacteria and iron-oxidizing bacteria. With a main focus on the management side, the role of environmental and health agencies in the monitoring of water for human consump- tion was addressed by Nasello et al. (2025). The work identified vulnerabilities in the water drinking supply chain, discovering the presence of cyanobacteria in nearly 20% of samples. At the same time, the authors reported a case study integrating into the Water Safety Plan the characterization, besides cyanobacteria and cyanotoxins, of different congeners of microcystins, viruses (particularly somatic coliphages), and spore-forming bacteria resistant to treatment processes, such as Clostridium perfringens and indicators of fecal contamination. The cited works highlighted the importance of developing monitoring plans incorporating collaboration with research insti- tutions where screening methods for cyanobacteria identification and cyanotoxin determination were already established. Such col- laborations were highlighted in the work by Austoni et al. (2025), which resumed a few results of an extensive survey on the cyanobacteria and cyanotoxins occurrence in the Alpine region, conducted in the framework of networking Interreg projects. The implications of the presence of cyanobacteria for human health and ecosystems were addressed in two papers coordinated by the Italian National Health Institute. The work by Testai (2024) provided an update on the relationship between cyanobacteria and cyanotoxin production, the toxicological risks connected with exposure, and the strategies for risk assessment and management. Focusing on the general theme of new emerg- ing contaminants, the work by Manganelli et al. (2024) ad- dressed the problems of the presence and spread of Antimicrobial Resistance Genes (ARGs) in cyanobacteria, fur- ther highlighting the necessity to enlarge the spectrum of target genes and molecules in cyanobacteria, well beyond the common legacy cyanotoxins. 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