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Cyanobacteria constitui um grupo de microorganismos procarióticos presentes nos ecossistemas aquáticos, sendo importantes produtores primários e responsáveis por grande parte das florações em ambientes dulcícolas. Desta forma, o presente estudo objetiva apresentar uma revisão da literatura disponível sobre os principais fatores promotores e as consequências das florações de cianobactérias. A ocorrência e manutenção das florações estão relacionadas à luz, temperatura, estabilidade da coluna d'água, pH, disponibilidade de nutrientes e herbivoria. Cianobactérias apresentam eficiente absorção de luz pela presença de ficobiliproteínas e melhor desenvolvimento em águas neutras a alcalinas. Temperaturas elevadas favorecem a estratificação térmica, aumentando a estabilidade da coluna d'água e estimulando a formação de florações. Nitrogênio e fósforo, principais nutrientes requeridos pelas cianobactérias, são responsáveis pela eutrofização, influenciando na magnitude, duração e composição das florações. Muitas espécies de cianobactérias apresentam baixa palatabilidade, sofrendo menor pressão por herbivoria, seja pelo grande tamanho, presença de mucilagem e potencial produção de toxinas. Florações de cianobactérias, as quais frequentemente culminam em má aparência e odor desagradável da água, podem também causar danos ecológicos, tais como alterações nas cadeias alimentares com potenciais efeitos na ciclagem de nutrientes, na biodiversidade e na saúde humana. Diversos fatores naturais e antropogênicos estão associados ao controle de florações, como sedimentação, hidrologia e concentração de nutrientes. Além destes, aplicação de algicidas, misturas verticais, redução do tempo de retenção e biomanipulação têm sido utilizadas objetivando minimizar ou eliminar as florações. No entanto, investigações mais detalhadas devem ser realizadas no sentido de manejar adequadamente os ecossistemas visando à prevenção e/ou controle efetivo das florações. Palavras-chave: Cianobactérias, florações, ecologia. ABSTRACT ECOLOGY OF CYANOBACTERIA: CAUSES AND CONSEQUENCES OF BLOOMS. Cyanobacteria form a group of prokaryotic microorganisms of aquatic ecosystems that are important primary producers and are usually responsible for blooms in freshwater habitats. This manuscript reviews the available literature on the factors promoting cyanobacterial blooms and their consequences. Such factors include light, temperature, stability of the water column, pH, nutrients, and grazing. Cyanobacteria can efficiently absorb light using phycobiliproteins, and develop better in neutral to alkaline water. Elevated temperatures can promote thermal stratification, estabilising the water column and triggering bloom formation. Nitrogen and phosphorus are the main nutrients required by cyanobacteria, which are also responsible for eutrophication, thus influencing the magnitude, duration and composition of blooms. Many species of cyanobacteria are unpalatable and grazing pressure can be reduced because of their large size, mucilage and even toxins. Cyanobacterial bloom...

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Assessment of water resources requires interdisciplinary studies that include multiple ecosystem aspects. This study evaluated the water quality of Juara Lagoon (ES, Brazil) based on physical and chemical variables, cytogenetic responses in Allium cepa and phytoplankton dynamics. Three sampling sites were defined and water samples were collected during two sampling periods. Analyses such as determination of photic zone, conductivity, and concentrations of nutrients and metals were conducted as well as cytotoxic, mutagenic, and genotoxic potentials using A. cepa test. The main attributes of phytoplankton community, such as total richness, total density, density by class, dominance, and diversity, were also evaluated. Results have revealed that Juara Lagoon has signs of artificial eutrophication at two sampling sites due to high levels of total phosphorus and ammonia nitrogen. Cytotoxic, genotoxic, and mutagenic potentials were detected as well as high concentrations of Fe and Mn. Furthermore, 165 phytoplankton taxa were recorded, with highest richness in Chlorophyceae and Cyanophyceae classes. In addition, Cyanophyceae presented as the highest density class. A. cepa test and phytoplankton community evaluation indicated that the ecological quality of Juara Lagoon is compromised.

In recent years, biodiesel production has attracted worldwide attention due to the awareness of fossil fuel depletion, and microalgae biomass is considered a promising raw material for its formulation. The present study evaluated the effects of different levels of nitrogen limitation (37.5, 18.75, 9.375 mg L -1 NaNO 3 ) on the growth, cell ultrastructure and biochemical composition of Picocystis salinarum as a potential raw material source for biodiesel. During a culture period of 20 days, the growth measurements were estimated, and cell density, dry weight and chlorophylls a, b content decreased with time as nitrogen limitation increase, however, carotenoids content increased. The high N limitation (9.375 mg L -1 ) had a highly signi cant effect on the accumulation of total lipid content (33.87% dry weight), carbohydrate content increase (30.98% dry weight), but protein content decrease (1.89% dry weight). The lipid content showed a differential FAME pro le with high saturated fatty acid values (996.08 µg g -1 dry weight) mainly C16:0, compare with the unsaturated ones that showed low values under high N limitation. The gradual increase of lipid content was also corroborated by transmission electron microscopy images with lipid droplet cell formation. Therefore, evaluation of the algal culture conditions such as N limitation, as a strategy to maximize lipid content and improve the fatty acid pro le in unexplored halophilic P. salinarum showed a potential biomass yield as a suitable candidate for biodiesel production.