We report the occurrence of cyanobacterial blooms and the presence of cyanotoxins in water samples from the Armando Ribeiro Gonçalves reservoir (06° 08' S and 37° 07' W), located in the state of Rio Grande do Norte, in the semiarid region of northeastern Brazil. The cyanobacterial species were identified and quantified during the rainy and dry seasons in the year 2000. Cyanotoxins such as microcystins, saxitoxins and cylindrospermopsins were analyzed and quantified using hPLC and ELISA methods. The mixed toxic blooms of Cylindrospermopsis raciborskii, Microcystis spp (M. panniformis, M. protocystis, M. novacekii) and Aphanizomenon spp (Aphanizomenon gracile, A. cf. manguinii, A. cf. issastschenkoi) were persistent and represented 90-100% of the total phytoplankton species. Toxic cyanobacterial blooms from the Armando Ribeiro Gonçalves reservoir were analyzed and found to have three phases in relation to the annual cycle. During the rainy season, an intense toxic bloom of Cylindrospermopsis raciborskii was recorded along with saxitoxins (3.14 µg.L -1 ). During the transition period, between the rainy and dry seasons, different species of Microscytis occurred and microcystin as high as 8.8 µg.L -1 was recorded. In the dry season, co-dominance of Cylindrospermopsis raciborskii, Microcystis spp and Aphanizomenon spp occurred and the concentrations of saxitoxin remained very low. Our results indicate the presence of microcystins (8.8 µg.L -1 ) and saxitoxins (3.14 µg.L -1 ) into the crude water, with increasing concentrations from the second fortnight of April to late May 2000. The occurrence of toxic blooms in this reservoir points to a permanent risk of cyanotoxins in supply waters, indicating the need for the implementation of bloom control measures to improve the water quality. Exposure of the local population to cyanotoxins through their potential accumulation in fish muscle must also be considered.Keywords: reservoir, semiarid, cyanobacteria, microcystin, saxitoxin. RESUMO Ocorrência de florações tóxicas de cianobactérias em um reservatório no semi-árido brasileiroNós relatamos a ocorrência de florescimentos de cianobactérias e a presença de cianotoxinas em amostras de água do reservatório Armando Ribeiro Gonçalves (06° 08' S; 37° 07' W) situado no Estado do Rio Grande do Norte, na região semi-árida do Brasil. Cianobactérias foram identificadas e quantificadas nos períodos seco e chuvoso do ano 2000. Cianotoxinas tais como, microcistinas, saxitoxinas e cilindrospermopsinas foram quantificadas por hPLC e ELISA. Florescimentos tóxicos mistos de Cylindrospermopsis raciborskii, Microcystis spp (M. panniformis, M. protocystis, M. novacekii)

Summary 1. Strong trophic cascades have been well documented in pelagic food webs of temperate lakes. In contrast, the limited available evidence suggests that strong cascades are less typical in tropical lakes. 2. To measure the effects of omnivorous tilapia on planktonic communities and water transparency of a small man‐made tropical lake, we performed a 5‐week in situ enclosure experiment with five densities of fish randomly allocated to 20 enclosures. Zooplankton and Phytoplankton biomasses as well as water transparency were measured weekly. 3. Results show that omnivorous tilapia significantly decreased the abundance of large Cladocerans, increased the abundance of small algae (greatest axial linear dimension <50 μm) and decreased water transparency as predicted by trophic cascade theory. 4. Therefore, omnivory was not a sufficient factor to prevent a trophic cascade in this pelagic community, although the cascade effect was weaker than reported from many north temperate, nutrient‐rich lakes.

RESUMOFlorações de cianobactérias em reservatórios resultam na perda da qualidade da água e em efeitos negativos para a saúde humana. Faz-se, portanto, necessário o monitoramento da ocorrência de cianobactérias e cianotoxinas, bem como a aplicação de medidas de controle das florações. Uma estratégia viável para esse controle é a manipulação dos estoques de peixes onívoros filtradores, como a tilápia do Nilo. Neste trabalho foram avaliados: i) a presença de cianobactérias (composição, densidade e biovolume, pelo método da sedimentação) e cianotoxinas (bioensaios com camundongos) em cinco reservatórios do semi-árido do estado do Rio Grande do Norte, em cinco campanhas de coletas, entre setembro de 2002 e março de 2004; e ii) as taxas de consumo per capita de cianobactérias filamentosas pela tilápia, através de dois experimentos em laboratório, utilizando populações naturais de cianobactérias (experimento I) e uma cultura de Cylindrospermopsis raciborskii (experimento II), após a exposição de indivíduos jovens de tilápia a um gradiente de biomassa de cianobactérias. O fitoplâncton nos reservatórios estudados apresentou dominância de cianobactérias, incluindo várias espécies toxigênicas (C. raciborskii, Microcystis spp., Aphanizomenon e Anabaena circinalis). Cianotoxinas foram evidenciadas em três dos cinco reservatórios. O consumo de cianobactérias (µg clorofila-a.peixe-1.dia-1) foi de 0,29 no experimento I e de 0,5 no experimento II. Populações abastecidas pelos reservatórios investigados estão potencialmente expostas aos efeitos negativos das cianotoxinas. Esta pesquisa sugere que é viável a estocagem da tilápia do Nilo no controle de florações de cianobactérias. Entretanto, fatores como a ictioeutrofização e o acúmulo de cianotoxinas na biomassa dos peixes devem ser levados em consideração antes que um programa de biomanipulação possa ser implementado. Palavras-chave: Cianobactérias, cianotoxinas, tilápia, biomanipulação, reservatórios ABSTRACT CYANOBACTERIA AND CYANOTOXINS IN RESERVOIRS OF RIO GRANDE DO NORTE STATE AND THE POTENCIAL CONTROL OF BLOOMS BY NILE TILAPIA (Oreochromis niloticus).Cyanobacteria blooms in reservoirs result in loss of water quality and negative effects to human health. To reduce these impacts the monitoring of the cyanobacteria and cyanotoxin occurrence as well as the application of measures to counteract the cyanobacteria blooms are made necessary. The manipulation of filter-feeding omnivorous fish stock, as Nile tilapia, has been proposed as an strategy for cyanobacteria bloom control. The present work aimed to evaluate: I) the presence of cyanobacteria (composition, density and biovolume by sedimentation technique) and cianotoxins (mouse bioassay) in five reservoirs located at the semi-arid region of Rio Grande do Norte state, in five sampling campaigns between September 2002 and March 2004; II) the per capita consumption rates of filamentous cyanobacteria by Nile tilapia through laboratory experiments using a natural population of cyanobacteria (experiment I) and a culture of Cylindr...

Aim:The rapid spread of cyanobacteria in water sources and reservoirs has caused serious environmental damage and public health problems, and consists in a problem that challenges the institutions responsible for providing water to the population. In this study, the quantification of microcystin, saxitoxins and cyanobacteria levels was performed over 3 years in the semi-arid reservoirs of Rio Grande do Norte (Brazil). In addition, we analyzed the seasonal distribution of cyanotoxins and the percentage of cyanobacteria and cyanotoxins which were above the limit established by Brazilian law.MethodsThe study was conducted between 2009 and 2011 in four dams with six sites: Armando Ribeiro Gonçalves (ARG) in Itajá, San Rafael (SR) and Jucurutu; Passagem das Traíras (PT); Itans and Gargalheiras (GARG). Cyanobacteria presence were quantified and identified and the presence of microcystins (MCYs) and saxitoxins (STXs) was investigated by ELISA.ResultsThe densities of cyanobacteria were found to be above the permitted in 76% of cases. The ELISA results showed that of the 128 samples analyzed, 27% were above the maximum allowed by the Brazilian Ministry of Health Order 2914/2011. A seasonal pattern for the presence of MCYs was found (0.00227 to 24.1954 µg.L–1), with the highest values in the rainy season. There was no clear seasonal pattern for STXs (0.003 to 0.766 µg.L–1).ConclusionsThis study showed the importance of establishing a water quality monitoring for human consumption and its potability standards since the concentration of MCYs in some samples was above the maximum limit allowed by Brazilian law, thus posing a risk to public health since the conventional water treatment is not able to eliminate these potent hepatotoxins.

AimAssess whether the assembly index is a suitable tool for biomonitoring of aquatic ecosystems of semi-arid environment.MethodsMonthly, samples were collected between October 2011 and May 2012 in Santa Cruz do Apodi (5°43'59"S; 46" 00 119 "W) and Pau dos Ferros (6°08'30.12" S; 038°10'59 880"W) reservoirs.ResultsThe Pau dos Ferros reservoir, shallow, turbid and eutrophic showed dominance of the functional group SN throughout the sample period. Total phytoplankton biovolume ranged between 20 and 70 mm³.L–1, the lowest values coincided with the increase of the mixing zone and transparency, which occasioned a change in composition of the phytoplankton community. Pau dos Ferros reservoir was categorized as poor for most of the sample period. The Santa Cruz do Apodi reservoir was characterized as meso-eutrophic, exhibiting low total phytoplankton biovolume (0.04 to 0,4 mm³.L–1) and greater diversity in the phytoplankton composition. It showed moderate condition during most of the period.ConclusionIn summary, the index Q reflected well the changes in phytoplankton composition, being a good indicator for biomonitoring of these systems.