Brazil has a history of blooms and contamination of freshwater systems by cyanobacterial toxins. The monitoring relevance of toxins from cyanobacteria in reservoirs for public supply is notorious given its high toxicity to mammals, included humans beings. The most recurrent toxins in Brazilian water bodies are microcystins (MC). However, the recent record of cylindrospermopsin (CyN) in northeastern Brazil, Pernambuco state, alerts us to the possibility that this could be escalating. This study reports occurrence of MC and CYN, quantified with ELISA, in 10 reservoirs, devoted to public drinking supply in northeastern Brazil. The composition and quantification of the cyanobacteria community associated with these water bodies is also presented. From 23 samples investigated for the presence of MC, and CyN, 22 and 8 out were positive, respectively. Considering the similarity of the cyanobacteria communities found in reservoirs from Pernambuco, including toxin-producing species associated to MC and CyN, we suggest that geographic spreading can be favored by these factors. These issues emphasize the need for increased monitoring of MC and CyN in drinking supply reservoirs in Brazil.

Harmful cyanobacterial blooms have caused several problems in freshwater environments due to their prolific growth and the harmful cyanotoxins produced by some species. The occurrence of these organisms has increased in recent decades due to climate change and eutrophication, although most studies are from temperate regions in the Northern hemisphere. This review presents data about cyanobacteria occurrence, dominance, and toxicity events in freshwater bodies in a semiarid region of Northeast Brazil, in the tropical Southern hemisphere. We performed a literature survey of cyanobacteria publications from 1930 to 2016. We made a list of all the dominant species registered in each state, noted their distribution and occurrence of dominance events involving one or more species, and the registered records of toxic blooms, including information about the toxins involved and the range of values. We selected 102 publications that described cyanobacteria Accepted Article www.jlimnol.it occurrence from states in Northeast Brazil; these publications included relevant contributions regarding cyanobacteria distribution, richness, density, and biomass. Forty-nine dominant species were recorded, with the most representation found in the state of Pernambuco (30 spp.). The genera with the highest occurrences were Microcystis, Cylindrospermopsis, Planktothrix, Dolichospermum (=Anabaena), and Geitlerinema, especially the species Cylindrospermopsis raciborskii, Microcystis aeruginosa, and Planktothrix agardhii. Episodes of toxic blooms were observed in four states. Microcystins, cylindrospermopsin, saxitoxins, and anatoxin-a(S) were found to be associated with these blooms. In Northeast Brazil, harmful cyanobacterial blooms are common in urban and public reservoirs. However, in recent years, cyanobacterial blooms in this region have been more intense and perennial, with high biomass occurring throughout the year.

In this study, the structure of phytoplankton communities in reservoirs with constant cyanobacteria blooms was evaluated using stability, persistence and species richness analyses. Samples were collected monthly from three reservoirs in northeastern Brazil between February 2012 and January 2013. The phytoplankton taxa were quantified under an inverted microscope. Stability was measured using Spearman's coefficient, based on the analysis of abundance rankings; persistence was measured using the inverse calculation for turnover; and richness was calculated using the number of species. Statistical analyses were used to determine the influence of abiotic variables on persistence and stability, and correlations were performed between persistence and stability and between species richness and stability. Cyanobacteria, particularly Cylindrospermopsis raciborskii (Woloszynska) Seenayya et Subba Raju, were observed in all samples. The results showed that stability and persistence were high, whereas species richness was low in the reservoir communities. The nutrients nitrate, nitrite and orthophosphate influenced persistence, whereas pH and ammonium explained stability. Persistence and stability were not significantly correlated, but a negative correlation was observed between species richness and stability.

Functional classifications are important for studies with phytoplankton, because they are based on ecological or morphological characteristics. We tested the interference of the macrophyte coverage in taxonomic and functional structure of phytoplankton community. Twelve small reservoirs were visited in September 2015 and May 2016 in semiarid regions of Brazilian northeast. Water samples were collected and abiotic variables were measured using a probe. Macrophyte coverage was recorded using the dot method. The microalgae were classified using taxonomic classification (taxa), morphological functional classification (MBFG) and functional groups (FG). We found 242 taxa, 22 FG and the seven MBFG. Phytoplankton presented an average biomass of 3.8 mg L −1 and a richness average of 38 species in dry period, while during the rainy season the biomass value was 6.2 mg L −1 and the richness, 33 species. The macrophytes had the highest average cover during the rainy season (63%) than the dry season (32%). Spearman analyses showed no correlation between total macrophyte coverage and biomass and richness (taxonomic and functional) of phytoplankton (P > 0.05). However, the growth form of emergent and free-floating macrophytes were selected as explanatory variables in the CCA model performed with the MBFG classification. This model presented greatest explanatory power (57%) when compared to FG classification (21%) and taxonomy (20%). Considering our results, using the MBFG classification is recommended for studies with similar sampling design, because it presents greater explanatory power and expresses the relationship between phytoplankton and aquatic macrophytes.

The installation of dams causes changes to the integrity of rivers and to the water cycle, performing an instrumental role in the organization of biological communities, including that of phytoplankton. In the present study, we analyzed the taxonomic composition of phytoplankton in two hydroelectric reservoirs on the São Francisco River, Itaparica and Xingó reservoirs. Samples were collected at quarterly intervals between December 2007 and September 2009, at 12 sampling stations in each reservoir, totaling 92 samples. We identified 110 species in the Itaparica reservoir and 136 in the Xingó reservoir, of which diatoms followed by green algae, played a major contribution to both reservoirs. Most of the species is rare and/or occasional. In the Itaparica reservoir, there were no very frequent species, although in the Xingó this category was represented by the diatoms Aulacoseira granulata (Ehrenberg) Simonsen and Fragilaria crotonensis Kitton. These results show that, despite the similarity in the composition of phytoplankton, the reservoirs studied certainly differed regarding their environmental conditions. Keywords: check list, freshwater, hydroelectric reservoir, microalgae, Northeast. Composição fitoplanctônica dos reservatórios de

This paper contributes to the inventory of cyanobacteria in freshwater environments in Northeastern Brazil. Forty-two samples were collected from 19 reservoirs between February 2009 and January 2010. Twenty-three species of cyanobacteria distributed among the orders Chroococcales (10), Oscillatoriales (8) and Nostocales (5) were identified, 12 of which constitute new records for the state of Pernambuco. The greatest degrees of species richness were recorded in three ecosystems (Alagoinha, Carpina and Ingazeira reservoirs). Microcystis was the most representative genus, with the greatest number of species (Microcystis novacekii (Komárek) Compère, Microcystis panniformis J.

A B S T R A C TThe vertical distribution of phytoplanktonic species in tropical regions responds quickly to the physicochemical factors of water with ecophysiological changes and biomass. Abiotic factors are responsible for the changes in the dominance of the different groups. The study analyzed the diversity and dominance of the phytoplankton community in a eutrophic reservoir localized in the semiarid region of Brazil. The samplings were conducted in nycthemeral cycles in different thermal regimes along a vertical profile. The biomass was determined by density and specific biovolume. Patterns of richness, diversity and specific dominance index were analyzed. The significant differences between the biotic data were analyzed by the ANOVA two-way and t-test. Similarity matrices were plotted using the Jaccard and Bray-Curtis indices with subsequent data ordination. 33 taxa were identified during the study. Differences in thermal patterns that are occurring in nycthemeral cycles showed changes in the structure of the phytoplankton community. The atelomictic event contributed to changing of the algal structure, especially in biomass, dominance, and diversity that shows significant differences between periods. The lowest diversity reported (< 1.03 bits.L -1 ) were influenced by monospecific dominance of the cyanobacteria C. raciborskii, thus recording greater biomasses, forming blooms throughout the study period. In the tropical eutrophic reservoirs, an algal bloom of cyanobacteria has persisted throughout the year, regardless of variations in the thermal regime, thereby reducing the phytoplankton diversity.