Effects of the submerged macrophyte Ceratophyllum demersum (Ceratophyllaceae) and the cladoceran Moina micrura (Cladocera: Moinidae) on microalgal interactions / Efectos de un macrófito sumergido Ceratophyllum demersum (Ceratophyllaceae) y un cladócero Moina micrura (Cladocera: Moinidae) sobre las interacciones de microalgas

Abstract Introduction: Cyanobacterial blooms in tropical water bodies are increasingly common, because of eutrophication and rising temperatures. Consequently, many freshwater systems are affected, by reducing water quality, biodiversity, and ecosystem services. With the increased frequency of harmful algal blooms, the development of biological tools to improve water quality is an urgent issue. Objective: To evaluate the effects of a submerged macrophyte and a cladoceran on the microcystin-producing cyanobacteria Microcystis aeruginosa (NPLJ-4) and the chlorophyte Raphidocelis subcapitata (BMIUFRPE-02) in mixed cultures. Methods: Two parallel experiments were carried out for ten days to evaluate the effects of the submerged macrophyte Ceratophyllum demersum and the cladoceran Moina micrura on microalgal interactions. Microalgal strains were cultivated in the ASM1 culture medium, under controlled laboratory conditions. The first experiment presented four treatments: M (C. demersum), Z (M. micrura), MZ (C. demersum and M. micrura), and C (control). Meanwhile, the second experiment consisted of five treatments, in which the microalgae were cultivated together at different Microcystis:Raphidocelis ratios: 1:0, 3:1, 1:1, 1:3, and 0:1. Biomass and growth rates of the strains were evaluated every two days, which were statistically treated with three-way or two-way repeated-measures ANOVA. Results: In the first experiment, M. aeruginosa was significantly inhibited in M and MZ treatments from the second day, and Z from the fourth, while R. subcapitata showed no reduction in its biomass in any treatment. On the other hand, R. subcapitata was stimulated from the eighth and tenth days in M treatment and only on the eighth day in Z treatment. In the second experiment, M. aeruginosa was significantly inhibited when cultivated with R. subcapitata in low ratios (Microcystis:Raphidocelis ratio of 1:3) throughout the experiment, while the chlorophyte was stimulated in that treatment. Conclusions: The coexistence of a cyanobacterium with a green alga did not alter the main negative response of M. aeruginosa to the submerged macrophyte and zooplankton but stimulated the green alga. Accordingly, the introduction of submerged macrophytes and cladocerans already adapted to eutrophic conditions, both isolated and combined, proved to be a good method to control cyanobacterial blooms without negatively affecting other coexisting phytoplankton species.

Resumen Introducción: Las proliferaciones de cianobacterias en los cuerpos de agua tropicales son cada vez más comunes, debido a la eutrofización y al aumento de las temperaturas. En consecuencia, muchos sistemas de agua dulce se ven afectados por la reducción de la calidad del agua, la biodiversidad y los servicios de los ecosistemas. Con el aumento de la frecuencia de la proliferación de algas nocivas, el desarrollo de herramientas biológicas para mejorar la calidad del agua es urgente. Objetivo: Evaluar los efectos de una macrófita sumergida y un cladócero sobre la cianobacteria productora de microcistina llamada Microcystis aeruginosa (NPLJ-4) y la clorofita Raphidocelis subcapitata (BMIUFRPE-02) en cultivos mixtos. Métodos: Se realizaron dos experimentos paralelos durante diez días para evaluar los efectos de la macrófita sumergida Ceratophyllum demersum y el cladócero Moina micrura sobre las interacciones microalgales. Se cultivaron cepas de microalgas en el medio de cultivo ASM1, en condiciones controladas de laboratorio. El primer experimento presentó cuatro tratamientos: M (C. demersum), Z (M. micrura), MZ (C. demersum y M. micrura) y C (control). El segundo experimento consistió en cinco tratamientos, en el que las microalgas se cultivaron juntas en diferentes proporciones de Microcystis:Raphidocelis: 1:0, 3:1, 1:1, 1:3 y 0:1. La biomasa y las tasas de crecimiento de las cepas se evaluaron cada dos días, y se trataron estadísticamente con ANOVA de medidas repetidas de dos o tres factores. Resultados: En el primer experimento, M. aeruginosa se inhibió significativamente en los tratamientos M y MZ a partir del segundo día, y en Z a partir del cuarto, mientras que R. subcapitata no mostró reducción de su biomasa en ningún tratamiento. Por otro lado, R. subcapitata fue estimulada a partir del octavo y décimo día en el tratamiento M y solo en el octavo día en el tratamiento Z. En el segundo experimento, M. aeruginosa se inhibió significativamente cuando se cultivó con R. subcapitata en proporciones bajas (proporción de Microcystis:Raphidocelis de 1:3) durante todo el experimento, mientras que la clorófita se estimuló en ese tratamiento. Conclusiones: La coexistencia de una cianobacteria con un alga verde no alteró la principal respuesta negativa de M. aeruginosa a la macrófita sumergida y al zooplancton, sino que estimuló al alga verde. En consecuencia, la introducción de macrófitos y cladóceros sumergidos ya adaptados a las condiciones eutróficas, tanto aislados como combinados, resultó ser un buen método para controlar las proliferaciones de cianobacterias sin afectar negativamente a otras especies de fitoplancton coexistentes.

Ecological impacts of freshwater algal blooms on water quality, plankton biodiversity, structure, and ecosystem functioning.

Harmful algal blooms are among the emerging threats to freshwater biodiversity that need to be studied further in the Anthropocene. Here, we studied freshwater plankton communities in ten tropical reservoirs to record the impact of algal blooms, comprising different phytoplankton taxa, on water quality, plankton biodiversity, and ecosystem functioning. We compared water quality parameters (water transparency, mixing depth, pH, electrical conductivity, dissolved inorganic nitrogen, total dissolved phosphorus, total phosphorus, chlorophyll-a, and trophic state), plankton structure (composition and biomass), biodiversity (species richness, diversity, and evenness), and ecosystem functioning (phytoplankton:phosphorus and zooplankton:phytoplankton ratios as a metric of resource use efficiency) through univariate and multivariate analysis of variance, and generalized additive mixed models in five different bloom categories. Most of the bloom events were composed of Cyanobacteria, followed by Dinophyta and Chlorophyta. Mixed blooms were composed of Cyanobacteria plus Bacillariophyta, Chlorophyta, and/or Dinophyta, while non-bloom communities presented phytoplankton biomass below the threshold for bloom development (10 mg L-1, WHO alert level 2). Higher phytoplankton biomasses were recorded during Cyanobacteria blooms (15.87-273.82 mg L-1) followed by Dinophyta blooms (18.86-196.41 mg L-1). An intense deterioration of water quality, including higher pH, eutrophication, stratification, and lower water transparency, was verified during Cyanobacteria and mixed blooms, while Chlorophyta and Dinophyta blooms presented lower pH, eutrophication, stratification, and higher water transparency. All bloom categories significantly impacted phytoplankton and zooplankton structure, changing the composition and dominance patterns. Bloom intensity positively influenced phytoplankton resource use efficiency (R2 = 0.25; p < 0.001), while decreased zooplankton resource acquisition (R2 = 0.51; p < 0.001). Moreover, Cyanobacteria and Chlorophyta blooms negatively impacted zooplankton species richness, while Dinophyta blooms decreased phytoplankton richness. In general, Cyanobacteria blooms presented low water quality and major threats to plankton biodiversity, and ecosystem functioning. Moreover, we demonstrated that biodiversity losses decrease ecosystem functioning, with cascading effects on plankton dynamics.

Growth of Microcystisstrains isolated from environments with the presence and absence of submerged macrophytes in coexistence with Ceratophyllum demersum

Cyanobacterial blooms can cause severe ecological and health problems in drinking water reservoirs. To alleviate this problem, allelopathically active submerged macrophytes can be used to reduce cyanobacterial growth. Accordingly, this study aimed to evaluate the sensitivity of strains of the Microcystis aeruginosacomplex isolated from reservoirs with the presence and absence of submerged macrophytes to the allelochemicals of Ceratophyllum demersum.A coexistence experiment was carried out between the submerged macrophyte C. demersum and four Microcystisstrains, with two treatments for each strain, one in coexistence with the submerged macrophyte (7 g L-1) and control (in the absence of the macrophyte). Two strains of M. aeruginosa(BMIUFRPE-06 and BMIUFRPE-07) and two of M. panniformis(BMIUFRPE-08 and BMIUFRPE-09) were used, which were isolated from Cajueiro (with submerged macrophytes) and Tapacurá (without submerged macrophytes) reservoirs, respectively. The biomass of Microcystisstrains from the reservoir without macrophytes (BMIUFRPE-08 and BMIUFRPE-09) was significantly inhibited in 96% (T-test: p 0.05; growth rate -ANOVA: p > 0.05). These results suggest that strains isolated from environments with submerged macrophytes are less sensitive to allelochemicals of these plants,as these strains may be adapted to the coexistence with submerged macrophytes.

Modeling cyanobacterial blooms in tropical reservoirs: The role of physicochemical variables and trophic interactions.

Understanding the importance of environmental variables on the dominance of cyanobacteria is crucial for appropriately managing water resources. Although studies about temperate and subtropical regions show a high influence of nutrients and temperature on blooms, this relationship is still unclear for the tropics. Accordingly, we hypothesized that nutrients and temperature are the main factors driving cyanobacterial blooms in tropical reservoirs, and those relationships are intensified by the zooplankton. To test these hypotheses, we constructed a structural equation model based on the monitoring of ten reservoirs from Northeast Brazil. We analyzed the effects of physicochemical variables and zooplankton on cyanobacterial blooms and the biomass of four morphotypes. Cyanobacterial biomass varied within the reservoirs, with bloom records (0.2-268.4 mg L-1) in all of them, primarily constituted by the colonial morphotype, followed by picocyanobacteria, heterocyted, and non-heterocyted filaments. The cyanobacterial community was driven mainly by chemical variables (55.14% of the variation), followed by physical (48.28%), and zooplankton (39.47%). Through the structural equation model, we demonstrated that total cyanobacterial biomass, as well as the morphotypes, were mainly influenced by omnivorous crustaceans and total dissolved phosphorus. Solar radiation, air temperature, mixing zone, and salinity were important to explain the biomass of the morphotypes. The model explained most of the variation in the picocyanobacterial blooms (79.8%), followed by total cyanobacteria (62.4%), heterocyted filaments (59.1%), non-heterocyted filaments (58.2%), and coccoids (55.1%). Zooplankton groups were also influenced by the physicochemical variables, which presented direct and indirect effects on cyanobacteria. Given the predictions of increased eutrophication, warming, and salinization, cyanobacterial blooms will become more intense in tropical reservoirs. Thus, restoring measures must be adopted to reduce bloom development, such as external phosphorus and salt loadings, and biomanipulation.

Temporal and spatial dynamics of phytoplankton near farm fish in eutrophic reservoir in Pernambuco, Brazil.

Spatial and temporal variations in phytoplankton communities in continental waters have received attention from limnologists, since they are differently influenced by many physico-chemical and biological factors. This study was undertaken with the aim to identify the environmental variables that influence the temporal and spatial dynamics of the phytoplankton near a fish farm in the Jucazinho reservoir, in a semi-arid region of Northeastern Brazil. Samples were taken from three sampling sites, at two depths during the rainy (Aug 2008, Feb and Mar 2009) and dry (Oct, Nov and Dec 2008) seasons. Phytoplankton was identified, density determined, and biomass values obtained. Concomitantly, abiotic analyses were performed for the characterization of the system. The reservoir was homogeneous with regard to the spatial-temporal variation in hydrological variables: water well oxygenated at the surface and anoxic at the bottom; pH ranging from neutral to alkaline; temperatures always above 25 degreeC; high turbidity; and high electrical conductivity at all sampling sites and both depths. For both seasons, there was limited nitrogen and high concentrations of phosphorus. Cyanophyta species were predominant, generally representing 80% of the phytoplankton biomass throughout practically the entire study, at all sampling sites and both depths. Co-dominance of cyanobacteria belonging to H1, MP, S1 and Sn associations was recorded in most of the months studied, except August 2008, when there was a substitution of the S1 association (Planktothrix agardhii) by the P association (Aulacoseira granulata). Water temperature, precipitation and pH were the parameters with the greatest influence over the temporal variation in phytoplankton, whereas the vertical distribution of the phytoplankton biomass was directly related to the availability of light in the water column. There were no spatial or temporal differences in water quality, likely due to the fact that the sampling sites were near to one another and received the same nutrients stemming from the rations given to the fish as well as their excrement. The predominance of cyanobacteria through the study was certainly due to the influence of the feeding products offered to and excreted from the fish, which eutrophicated the system. In temporal terms, the change in the algal structure is explained by the change in the physical conditions of the water between the surface and bottom, as well as the climatologic conditions, especially the change in wind direction, with the consequent fetch of the water.

Structure and dynamics of phytoplankton in an Amazon lake, Brazil.

Natural lake systems represent important reservoirs for residential water supply, fish production, recreational activities and enjoyment of their natural beauty. Nevertheless, human impacts may affect their health status resulting in degradation and loss of biodiversity. The aim of the present study was to obtain data on the health status of a natural lake located in an indigenous reservation in the Brazilian Amazon, using the phytoplankton community changes along the rainy (June) and dry (November) seasons of 2006. We collected water (temperature, pH, Secchi depth and conductivity) and phytoplankton samples from the subsurface, middle of the water column, and approximately 30 cm above the bottom, over 24-hour sampling periods, from a central station in the lake. Samples taken from biotic and abiotic variables were correlated using canonical correspondence analysis (CCA). Results showed that the lake exhibited high temperatures in both seasons, and showed thermal stratification only during the rainy season. Dissolved oxygen exhibited a clinograde pattern in the rainy season and high oxygen in the hypolimnion in the dry season. In the rainy season, the water near the bottom was acidic, turbid and had a greater concentration of phosphorus. Dissolved oxygen, conductivity, pH, nitrite, total phosphorus and total dissolved phosphorus exhibited diel variations in the rainy season, whereas water temperature, dissolved oxygen, total nitrogen and total dissolved phosphorus exhibited significant differences between hours of the day in the dry season. The phytoplankton was represented by 39 taxa, and Chlorophyta showed the greatest species richness, totaling 25 taxa. Among Chlorophyta, desmids were the most diverse, accounting 52%. Bacillariophyta (nine species) was the second most diverse group. Cyanophyta was represented by three species, including Merismopedia tenuissima, the most abundant taxon. Despite the occurrence of taxa that indicate organic pollution, their biomass and frequency indicate that the system is not currently threatened. Lake Caracaranã is an oligotrophic system, with low algal density and isolated blooming episodes due to its shallow depth.

Genetic polymorphism in brazilian microcystis spp. (Cyanobacteria) toxic and non-toxic through RFLP-PCR of the cpcBA-IGS

The escalating occurrence of cyanobacterial toxic blooms demands a better understanding of genetic variability as an auxiliary expedient in species identification, collaborating with the monitoring of water destined to public supply. This study aimed at the unraveling of genetic polymorphism in the toxic and nontoxic strains of Microcystis (Cyanobacteria) species, isolated from diverse Brazilian localities through the RFLP-PCR technique applied to the c-phycocyanin encoding operon and its intergenic spacer (cpcBA-IGS). Eighteen strains belonging to M. aeruginosa, M. panniformis, M. protocystis and M. wesenbergii, plus two other unidentified strains, were analyzed by means of the morphological and molecular data. The molecular data constituted three groups with low similarity values unrelated to the geographical origin, toxicity or morphospecies. A high genetic variability among the studied populations was unveiled by the results. Brazilian populations of Microcystis spp. displayed high genetic diversity when compared to those from Australia, Japan, United States and Europe. This ample genetic diversity could be observed through the diverse eletrophoretic profiles obtained among the strains from a single species. The presence of toxic and non-toxic strains was observed in the same species, as M. aeruginosa.

A ocorrência de florações de cianobactérias tóxicas demanda um melhor entendimento da variabilidade genética como um instrumento auxiliar na identificação de espécies colaborando, assim, com o monitoramento de águas destinadas ao abastecimento público. Este estudo objetivou o conhecimento do polimorfismo genético de linhagens tóxicas e não tóxicas de espécies de Microcystis (Cyanobacteria), isoladas de diversas localidades brasileiras, utilizando a técnica molecular RFLP-PCR para o operon que codifica para a c-ficocianina e seu espaçador intergênico (cpcBA-IGS). Foram analisadas dezoito linhagens pertencentes as espécies Microcystis aeruginosa, M. panniformis, M. protocystis, M. wesenbergii e duas outras não identificadas através de dados morfológicos e moleculares. Os resultados moleculares formaram três agrupamentos com baixos valores de similaridade entre si os quais não foram relacionados à origem geográfica, toxicidade ou morfoespécies. As populações brasileiras de Microcystis spp. apresentaram alta diversidade genética quando comparadas com as da Austrália, Japão, Estados Unidos e Europa. Esta ampla diversidade genética pode ser vislumbrada através de diversos perfis eletroforéticos obtidos entre linhagens de uma mesma espécie. Nós encontramos a presença de linhagens tóxicas e não tóxicas em uma mesma espécie, como em M. aeruginosa.

Structure and dynamics of phytoplankton community in the Botafogo Reservoir-Pernambuco-Brazil

The aim of the present study was to investigate the structure and dynamics of the phytoplankton in the Botafogo reservoir-PE-Brazil. Phytoplankton assemblages were identified from current literature and density was estimated using an inverted microscope. Concurrently to the sampling of biotic variables, measurements of abiotic parameters, such as water temperature, dissolved oxygen and pH, were determined using field probes and transparency was determined with a Secchi disk. Total phosphorus and total nitrogen concentrations were determined in laboratory. A total of 24 taxa were identified. Chlorophyta presented the greatest number of species. Species diversity in the reservoir was low throughout the study period. Principal component analysis revealed that Trachelomonas volvocina, Chlorella vulgaris, Euglena sp. and Peridinium gatunense were directly correlated with oxygen, turbidity and total nitrogen; Planktosphaeria gelatinosa, P. gatunense and Euglena sp. were directed correlated with total nitrogen; rainfall explained the occurrence of Monoraphidium arcuatum and Chlorella vulgaris.

O objetivo do presente estudo foi investigar a estrutura e dinâmica do fitoplâncton no reservatório de Botafogo-PE-Brasil. A comunidade fitoplanctônica foi identificada com literatura atualizada e a densidade estimada usando microscópio invertido. Concomitantemente as coletas das variáveis bióticas, foram medidos alguns parâmetros abióticos como temperatura da água, oxigênio dissolvido, condutividade e pH usando sondas de campo e transparência com disco de Secchi. Concentrações de fósforo total e nitrogênio total foram determinados em laboratório. Vinte e quatro táxons foram identificados tendo Chlorophyta apresentado maior número de espécie. A diversidade de espécie no reservatório foi baixa durante todo o período de estudo. A análise de componentes principais mostrou que Trachelomonas volvocina, Chlorella vulgaris, Euglena sp. e Peridinium gatunense esteve diretamente correlacionada com oxigênio dissolvido, turbidez e nitrogênio total. P. gelatinosa, Peridinim gatunense e Euglena sp. estiveram diretamente relacionada com nitrogênio total; a chuva explicou a ocorrência de Monoraphidium arcuatum e Chlorella vulgaris.

Structure of the phytoplankton in a water supply system in the State of Pernambuco - Brazil

The aim of this work was to study the phytoplankton community composition at limnetic environment in Pernambuco, Brazil. Samplings were carried out from April/2001 to March/2002. Samples to analyses the biotic variables were taken using a recipient with a large overture, at the subsurface and with a Van Dorn bottle at the bottom. The rainfall data were recorded and the water transparency was used to calculate the light attenuation coefficient, photic zone and the determination of trophic state index. The concentrations of total phosphorus and total nitrogen were determined in a typical dry and rainy month. Equitability, also the, similarity and diversity indexes and the densities and correlation of total densities among depths were calculated. Forty-five taxa were identified in Chlorophyta (21spp), Cyanophyta (17spp) and Bacillariophyta (7spp), while flagellates were quantified in groups without identification. Cyanophyta presented highest diversity at both the depths and Planktothrix agardhii was the highest density species. Significant differences were not observed between subsurface and bottom densities. Results showed that the reservoir was eutrophicated and presented high densities of Cyanophyta.

O objetivo deste trabalho foi o estudo da comunidade fitoplanctônica em ambiente limnético de Pernambuco, Brasil. As amostras foram coletadas de abril/2001 a março/2002. As amostras para análises abióticas foram coletadas na superfície da água e destinadas às análises bióticas foram coletadas na subsuperfície e no fundo, sendo fixadas com solução de lugol e quantificadas usando microscópio invertido. Equitatividade, índices de similaridade e diversidade foram calculados, bem como correlação entre as profundidades. 45 táxons foram identificados, pertencentes as Chlorophyta (21spp), Cyanophyta (17spp) e Bacillariophyta (7spp). Os flagelados foram apenas quantificados, mas não foram identificados. Cyanophyta apresentou a mais alta diversidade em ambas as profundidades e Planktothrix agardhii foi a espécie que apresentou a maior densidade. Diferenças significativas quanto às densidades não foram observadas entre subsuperfície e fundo. O reservatório encontra-se eutrofizado, sendo encontradas altas densidades de Cyanophyta durante todo o período de estudo.

O estado da arte da biodiversidade de rotíferos planctônicos de ecossistemas límnicos de Pernambuco / State of the art in planktonic rotifers biodiversity from freshwater environments in the state of Pernambuco (Brazil)

Este trabalho apresenta uma avaliação do estado da arte da biodiversidade de rotíferos planctônicos de alguns ecossistemas aquáticos continentais para Pernambuco (Brasil). Um levantamento bibliográfico foi realizado e a maior parte das pesquisas enfocou aspectos sazonais e estado trófico dos ecossistemas. Pelo menos 19 locais foram estudados no tocante aos rotíferos. O Sertão é a região mais estudada. Nesta pesquisa foram registradas 64 espécies de rotíferos planctônicos, distribuídas em 18 famílias e 29 gêneros. As espécies mais freqüentes nos locais estudados foram Keratella tropica e Brachionus falcatus, mostrando que a maior parte dos estudos foi realizada na zona limnética. Os resultados sugerem ainda a necessidade de mais pesquisas sobre a biodiversidade deste grupo em locais localizados na Zona da Mata e no Agreste, bem como em ecossistemas lóticos e nas zonas litorâneas dos locais, tendo em vista a carência de informações.

The state of the art in planktonic rotifers biodiversity from some freshwater ecosystems was elaborated for the state of Pernambuco (Brazil). A bibliographic survey was done and most studies focused seasonal aspects and trophic state of the ecosystems. At least 19 continental aquatic environments related to rotifer researches have been studied. The Sertão area was the most studied. The present survey registered 64 species of planktonic rotifers, distributed in 18 families and 29 genera. The most frequent species were Keratella tropica and Brachionus falcatus, showing that most studies were done in the limnetic zone. The results showed the need for more research on the biodiversity of this group in ecosystems located in Zona da Mata and Agreste areas, as well as in lotic systems and in the littoral zones, in view of the lack of information.

A novel rhythm of microcystin biosynthesis is described in the cyanobacterium Microcystis panniformis Komárek et al.

The presence of microcystins (MCY) in the cyanobacteria Microcystis panniformis Komárek et al. is reported for the first time. This strain of cyanobacterium has been isolated from Barra Bonita, an eutrophicated water reservoir in São Paulo state, Brazil. The identification of M. panniformis was confirmed by both traditional morphological analysis and the phycocyanin intergenic spacer sequences. MCY-LR and [Asp(3)]-MCY-LR were identified in this strain after HPLC purification and extensive ESI-MS/MS analysis. Their levels in this strain were determined by HPLC and ranged from 0.25 to 2.75 and 0.08 to 0.75 fmol/cell, respectively. Analyzing the levels of MCY-LR and [Asp(3)]-MCY-LR in different times during the light:dark (L:D) cycle, it was found that levels of MCYs per cell were at least threefold as high during the day-phase than during the night-phase. This may be associated to the biological clock since prokaryotic cyanobacteria express robust circadian (daily) rhythms under the control of a timing mechanism that is independent of the cell division cycle. Our findings also showed the same pattern under light:light (L:L) cycle.