Cyanobacteria Blooms in the Baltic Sea: A Review of Models and Facts

The ecosystem of the Baltic Sea is endangered by eutrophication. This has triggered expensive international management efforts. Some of these efforts are impeded by natural processes such as nitrogen-fixing cyanobacteria blooms that add bioavailable nitrogen to the already over-fertilized system and thereby enhance primary production, export of organic matter to depth, and associated oxygen consumption. Controls of cyanobacteria blooms are not comprehensively understood, and this adds to the uncertainty of model-based projections into the warming future of the Baltic Sea. Here we review our current understanding of cyanobacteria bloom dynamics. We summarize published field studies and laboratory experiments and dissect the basic principles ingrained in state-of-the-art coupled ocean–circulation biogeochemical models

Early detection and the importance of environmental drivers for the invasive cyanobacterium Raphidiopsis raciborskii

Freshwater habitats often experience species loss, with the greatest pressures coming from land use alterations and the establishment of non-native species as they become invasive. One species of concern is the tropical invasive freshwater cyanobacterium Raphidiopsis raciborskii, currently expanding its geographic distribution towards northern regions of Europe. As a toxin-producing, bloom-forming species, population growths of R. raciborskii can negatively affect local biodiversity and ecosystem services. Hence, in this study, I wanted to evaluate and validate (i) the geographical extent of suitable habitats, (ii) its competitive capacities with a native phytoplankton assemblage and (iii) its adaptive capabilities when moved from ideal to colder temperatures. To identify suitable colonization areas, I used Species Distribution Models (SDMs), which revealed suitable habitats in areas where the invasive cyanobacterium has not been recorded, i.e. several parts of Europe including south-eastern Sweden. However, there were some inconsistencies between SDM results and the field studies used to validate the SDM prediction, where only a few of the European screened lakes matched with the SDM prediction. To better understand the competitive success of R. raciborskii we performed a laboratory study using different nutrient and temperature conditions and, as competitors, an assembly of phytoplankton species typically found in Scandinavian freshwaters. Results confirmed the importance of temperature on R. raciborskii growth and its ability to withstand suboptimal environments. The physiological changes and gene expressions of R. raciborskii, when transferred from optimal to suboptimal temperatures, were tested through a differential transcriptomic experiment. Results showed a difference in gene expression in different treatments, with a downregulation of genes in the suboptimal temperature. Although R. raciborskii has not been recorded in Sweden, it is a well-established invasive species in many European lakes. Combined results from this thesis show that R. raciborskii meets the climatic conditions matching with the south-eastern parts of Sweden. If able to surpass physical and ecological barriers, due to its ability to withstand a wide-range of environments, it might be able to survive in lakes with less favorable conditions and bloom when conditions become ideal. To be able to prevent and contain the expansion of this invasive species in northern European lakes, proactive monitoring programs with high temporal and spatial frequency are needed in combination with broad information campaigns to minimize further spread to other freshwater system

Predicting the effects of climate change on freshwater cyanobacterial blooms requires consideration of the complete cyanobacterial life cycle

To date, most research on cyanobacterial blooms in freshwater lakes has focused on the pelagic life stage. However, examining the complete cyanobacterial life cycle—including benthic life stages—may be needed to accurately predict future bloom dynamics. The current expectation, derived from the pelagic life stage, is that blooms will continue to increase due to the warmer temperatures and stronger stratification associated with climate change. However, stratification and mixing have contrasting effects on different life stages: while pelagic cyanobacteria benefit from strong stratification and are adversely affected by mixing, benthic stages can benefit from increased mixing. The net effects of these potentially counteracting processes are not yet known, since most aquatic ecosystem models do not incorporate benthic stages and few empirical studies have tracked the complete life cycle over multiple years. Moreover, for many regions, climate models project both stronger stratification and increased storm-induced mixing in the coming decades; the net effects of those physical processes, even on the pelagic life stage, are not yet understood. We therefore recommend an integrated research agenda to study the dual effects of stratification and mixing on the complete cyanobacterial life cycle—both benthic and pelagic stages—using models, field observations and experiments

ICTC12 Abstract Book

Abstract book for the 12th International Conference on Toxic Cyanobacteria

Phytoplankton community structure in one sector of Guanabara Bay (RJ, Brazil) during 2011 and 2012

This study analyzed the temporal variability of phytoplankton assemblages in the surface waters of Guanabara Bay (RJ, Brazil), at six stations in front of Icaraí Inlet from April/2011 to April/2012. Our results highlight the great contribution of diatoms, dinoflagellates and cyanobacteria, represented by 111 taxa typical of estuarine and coastal areas. The coexistence of benthic and planktonic species suggests considerable hydrodinamism in these waters. All variables were homogeneous (p >; 0.05) between the stations, but differed between sampling periods. On average, phytoplankton abundance (107 cells.L-1) was higher than that of other estuaries and its temporal behavior was closely correlated (p ; 0,05) entre as estações de coleta para todas as variáveis, mas diferenças entre campanhas. A densidade média (107 cel.L-1) foi superior à de outros sistemas estuarinos e seu comportamento temporal esteve altamente correlacionado (p < 0,01) com diatomáceas e cianobactérias. Por sua vez o padrão de distribuição da riqueza (7 a 27 táxons) apresentou alta correlação positiva (p < 0,01) com dinoflagelados e diatomáceas. Baixos índices de diversidade (< 2,0 bits.cel-1) em 90% das amostras reafirmaram o equilíbrio instável do sistema, típico de ambientes sujeitos à eutrofização. A análise da estrutura das populações estabeleceu que 10% dos táxons são residentes, 12% visitantes e 78% acidentais, reafirmando a influência do aporte continental e/ou águas oceânicas. Entre os táxons "típicos", destacaram-se cianobactérias da Ordem Oscillatoriales, diatomáceas Ceratoneis closterium (=Cylindrotheca closterium) e Leptocylindrus minimus e o dinoflagelado Prorocentrum triestinum

Controls on microalgal community structures in cryoconite holes upon high Arctic glaciers, Svalbard

Glaciers are known to harbor surprisingly complex ecosystems. On their surface, distinct cylindrical holes filled with meltwater and sediments are considered as hot spots for microbial life. The present paper addresses possible biological interactions within the community of prokaryotic cyanobacteria and eukaryotic microalgae (microalgae) and relations to their potential grazers, additional to their environmental controls. Svalbard glaciers with substantial allochthonous input of material from local sources reveal high microalgal densities. Small valley glaciers with high sediment coverages and high impact of birds show high biomasses and support a high biological diversity. Invertebrate grazer densities do not show any significant negative correlation with microalgal abundances, but a positive correlation with eukaryotic microalgae. Most microalgae found in this study form large colonies ( 25 μm), which may protect them against invertebrate grazing. This finding rather indicates grazing as a positive control on eukaryotic microalgae by nutrient recycling. Density differences between the eukaryotic microalgae and prokaryotic cyanobacteria and their high distinction in RDA and PCA analyses indicate that these two groups are in strong contrast. Eukaryotic microalgae occurred mainly in unstable cryoconite holes with high sediment loads, high N : P ratios, and a high impact of bird guano, as a proxy for nutrients. In these environments autochthonous nitrogen fixation appears to be negligible. Selective wind transport of Oscillatoriales via soil and dust particles is proposed to explain their dominance in cryoconites further away from the glacier margins. We propose that, for the studied glaciers, nutrient levels related to recycling of limiting nutrients is the main factor driving variation in the community structure of microalgae and grazers

Processos ecológicos envolvidos na distribuição da diversidade genética e taxonômica de cianobactérias de ecossistemas aquáticos continentais

As cianobactérias são microrganismos procariotos, capazes de realizar fotossíntese oxigênica. Ao longo de sua longa história evolutiva na Terra, adaptações genéticas, bioquímicas e fisiológicas garantiram a estes procariotos a sua perpetuação em praticamente toda a superfície terrestre. As cianobactérias se distribuem ao longo de habitats terrestres e aquáticos, em associação com outros seres vivos, e mesmo em ambientes extremos. Em ecossistemas aquáticos, especialmente, as cianobactérias são encontradas em alta abundância e são as maiores responsáveis pela produção primária. Além disso, cianobactérias podem formar florações e liberar toxinas em ambientes aquáticos, o que as torna intimamente relacionadas às condições da água e à conservação dos ecossistemas aquáticos. Estudos sobre padrões de distribuição de cianobactérias têm crescido na literatura e são importantes uma vez que podem alertar riscos de floração, e também para compreender melhor a ecologia do grupo, como habilidades de dispersão e preferências de habitat. Nesse contexto, a presente tese teve como objetivo geral explorar os fatores ecológicos que influenciam a distribuição das cianobactérias, com foco em ecossistemas de água doce. Para isso, a tese foi estruturada em três capítulos, cada qual com o objetivo central de: (I) sintetizar, através de uma ampla revisão bibliográfica, padrões biogeográficos de cianobactérias e as evidências sobre os processos ecológicos que estruturam esses padrões; (II) reconstruir as histórias filogeográficas de duas cianobactérias cosmopolitas de vida livre (Raphidiopsis raciborskii e Microcystis aeruginosa), com base na diversidade genética do gene 16S rRNA, a fim de explorar se suas distribuições atuais podem ser atribuídas aos mesmos processos ecológicos; (III) explorar os padrões de diversidade alfa e beta de cianobactérias planctônicas e perifíticas (associadas à macrófita Scirpus californicus) em um sistema de lagoas subtropicais e como a influência de variáveis ambientais varia entre cianobactérias de vida livre (planctônicas) e de vida associada (perifíticas). Os principais achados desta tese foram: (I) tanto fatores ambientais quanto históricos são importantes na distribuição das cianobactérias; no entanto, padrões de distribuição dependem intimamente do conceito de espécie, que ainda é debatido para procariotos, incluindo cianobactérias, escalas espaciais e ambientais, e os vieses das metodologias aplicadas nos estudos; (II) M. aeruginosa e R. raciborskii apresentaram maior diversidade genética em latitudes tropicais e evidência de expansão populacional recente. No entanto, embora ambas as espécies sejam consideram cosmopolitas, a filogeografia de R. raciborskii indica uma interação entre deriva e alguma limitação de dispersão, ao passo que M. aeruginosa parece ter uma alta frequência de dispersão intercontinental; (III) assembleias de cianobactérias planctônicas e perifíticas são distintas e estruturadas por diferentes fatores ecológicos. Enquanto a variação nas cianobactérias planctônicas foi determinada principalmente pelas condições da água, as cianobactérias perifíticas foram influenciadas apenas pela abundância de outros táxons bacterianos. Em geral, a presente tese contribuiu para o entendimento dos fatores envolvidos na distribuição das cianobactérias e como eles variam entre diferentes táxons, escalas espaciais e tipos de habitat. Ainda, forneceu perspectivas para investigações futuras nesse campo, a fim de contribuir para uma maior compreensão dos processos ecológicos que moldam a distribuição desse importante grupo de procariotos.Cyanobacteria are prokaryotic microorganisms capable of performing oxygen photosynthesis. Throughout its long evolutionary history on Earth, genetic, biochemical and physiological adaptations have allowed to these prokaryotes to inhabit the entire terrestrial surface. Cyanobacteria are distributed throughout terrestrial and aquatic habitats, in association with organisms, and even in extreme environments. In aquatic ecosystems, especially, cyanobacteria are typically abundant and responsible for most of the primary production. In addition, cyanobacteria can form blooms and release toxins in aquatic environments, so that cyanobacteria are closely related to water conditions and conservation of aquatic ecosystems. Studies on cyanobacteria distribution patterns have increased in the literature and are important since they are able to alert the risks of cyanoblooms, and also to better understand the ecology of the group, such as dispersal abilities and habitat preferences. In this context, the present thesis aimed to explore the ecological factors that influence the distribution of cyanobacteria, focusing on freshwater ecosystems. For this, this thesis was structured in three chapters, with the main goals of: (I) to review the biogeographic patterns of cyanobacteria with focus on molecular data and the evidences from the published literature for the processes driving these patterns; (II) to reconstruct the phylogeographic histories of two free-living cosmopolitan cyanobacteria (Raphidiopsis raciborskii and Microcystis aeruginosa), based on the genetic diversity of the 16S rRNA gene, in order to explore whether their current distributions could be attributed to the same ecological processes; (III) to explore alpha and beta diversity patterns of planktonic and periphytic (associated to Scirpus californicus) cyanobacteria in a subtropical lake system, and how the influence of niche-related variables varies between free-living (planktonic) and surface-associate (periphytic) assemblages. In summary, the main findings of this thesis were that: (I) both environmental and historical factors are important in structuring cyanobacteria variation across time and space, however, distribution patterns are closely dependent on the concept of species, which is still debated for prokaryotic microorganisms, including cyanobacteria, spatial and environmental scales, and the biases of the molecular methodologies applied in the studies; (II) R. raciborskii and M. aeruginosa had greater genetic diversity in tropical latitudes and showed evidence of recent population expansion. However, although both species are considered cosmopolitan, the phylogeography of R. raciborskii indicates an interaction between drift and some dispersal limitation, whereas M. aeruginosa seems to have a high frequency of intercontinental dispersal; (III) planktonic and periphytic cyanobacteria assemblages are distinct and structured by different ecological factors. While the variation in planktonic cyanobacteria was mainly determined by water conditions, periphytic cyanobacteria were influenced only by the abundance of other bacterial taxa. In general, this thesis has contributed to the understanding of the factors involved in the distribution of cyanobacteria, and how they vary between different taxa, spatial scales and habitat types. It also provided perspectives for future research in this field, in order to contribute to a greater understanding of the ecological processes that shape the distribution of this important group of prokaryotes

Hydrometeorological and climatic control over lake phytoplankton: the importance of time scales

[eng] In the present thesis we focus on the two extremes of the wind speed – storms and atmospheric stilling – and analyse their impacts on lake environments and phytoplankton dynamics over short and long periods. As we realised the importance of the time scale in the context of our wind effect studies, we decided to have a closer look at other environmental data in the Lake Võrtsjärv database addressing the questions how the variability in environmental factors (thermal, wind, light- and water-level regimes) and phytoplankton variables is partitioned among different time scales from days to decades and whether matching shares can help to determine the leading factors responsible for phytoplankton dynamics