Exposure to toxic Microcystis via intact cell ingestion and cell crude extract differently affects small-bodied cladocerans.

Cyanobacterial blooms are increasingly common in aquatic environments worldwide. These microorganisms cause concern due to their ability to produce cyanotoxins. Aquatic organisms, especially zooplankton, are exposed to cyanobacterial toxins by different routes, depending on the bloom phase. During cyanobacterial dominance, zooplankton is exposed to cyanotoxins through the ingestion of cyanobacterial cells, while at the bloom senescence, dissolved toxins are the most representative route. In this study, we assessed the effects of a microcystin-producing strain of Microcystis aeruginosa (NPLJ-4) on clones of the tropical small cladocerans Macrothrix spinosa (two clones) and Ceriodaphnia cornuta (one clone) exposed to intact cells and aqueous cell crude extracts. Short-term toxicity assays and life-table experiments were performed to assess the effects of the toxic M. aeruginosa on the survival and life history of the cladocerans. In the short-term toxicity assay, we found that cladocerans were more affected by intact cells. Both clones of M. spinosa were more affected when exposed to intact cells, while C. cornuta displayed about 5-fold more resistance. On the other hand, crude extracts had a low impact on cladocerans' survival. Also, we observed a significant decrease in survival, fecundity, and growth of animals exposed to sublethal and environmentally relevant concentrations of M. aeruginosa cellular biomass. However, even at high concentrations of dissolved microcystins, the crude extract did not have significant effects on the life history parameters of the cladocerans. Although they can be found during cyanobacterial bloom events, small-bodied cladocerans are still affected by toxic Cyanobacteria depending on the exposure route.

Effects of increased zooplankton biomass on phytoplankton and cyanotoxins: A tropical mesocosm study.

Zooplankton are important biocontrol agents for algal blooms in temperate lakes, while their potential in tropical and subtropical environments is not well understood. The aim of the present study was to evaluate the influence of increased zooplankton biomass on phytoplankton community and cyanotoxins (microcystins and saxitoxin) content of a tropical reservoir (Ipojuca reservoir, Brazil) using in situ mesocosms. Mesocosms consisted of 50L transparent polyethylene bags suspended in the reservoir for twelve days. Phytoplankton populations were exposed to treatments having 1 (control), 2, 3 and 4 times the biomass of zooplankton found in the reservoir at the beginning of the experiment. Filamentous cyanobacteria such as Planktothrix agardhii and Cylindrospermopsis raciborskii were not negatively influenced by increasing zooplankton biomass. In contrast, the treatments with 3 and 4 times zooplankton biomass negatively affected the cyanobacteria Aphanocapsa sp., Chroococcus sp., Dolichospermum sp., Merismopedia tenuissima, Microcystis aeruginosa and Pseudanabaena sp.; the diatom Cyclotella meneghiniana; and the cryptophyte Cryptomonas sp. Total microcystin concentration both increased and decreased at different times depending on zooplankton treatment, while saxitoxin level was not significantly different between the treatments and control. The results of the present study suggest that zooplankton biomass can be manipulated to control the excessive proliferation of non-filamentous bloom forming cyanobacteria (e.g. M. aeruginosa) and their associated cyanotoxins.

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 25ºC; 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 wáter 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. Rev. Biol. Trop. 60 (2): 581-597. Epub 2012 June 01.

Las variaciones espaciales y temporales en las comunidades de fitoplancton en las aguas continentales han recibido la atención de limnólogos, ya que están influenciados de manera diferente por muchos factores físico-químicos y biológicos. El objetivo del presente trabajo fue identificar las variables ambientales que ejercieron influencia sobre la dinámica temporal y espacial de la comunidad fitoplanctónica cerca a una granja pisícola en la represa de Jucazinho, la cual se encuentra en la región semiárida brasilera. Las recolecciones fueron realizadas en tres estaciones de monitoreo a dos profundidades, durante los periodos lluviosos (agosto 2008 y febrero, marzo 2009) y de sequía (octubre, noviembre y diciembre 2008). El fitoplancton fue identificado y su densidad determinada, y posteriormente convertida a biomasa. También se realizaron análisis abióticos para caracterizar el sistema. La represa resultó homogénea en cuanto a la variación espacio-temporal de las variables hidrológicas, agua oxigenada en la superficie y anóxica en el fondo, pH varía neutro-alcalino, temperaturas superiores a 25°C y conductividad y turbidez elevadas. En los dos periodos estacionales fueron observadas limitaciones de nitrógeno y elevadas concentraciones de fósforo. Las Cyanophytas fueron predominantes en el ambiente y representaron en general más del 80% de la biomasa fitoplanctónica durante prácticamente todo el periodo de estudio en todas las estaciones y profundidades de recolecta. La co-dominancia de cianobacterias pertenecientes a las asociaciones H1, MP, S1 y Sn, fue registrada durante la mayor parte del periodo de estudio, excepto en ago/2008, cuando ocurrió una sustitución de la asociación S1 (Planktothrix agardhii) por P (Aulacoseira granulata) en la represa. Los factores que tuvieron más influencia sobre la variación temporal del fitoplancton fueron temperatura del agua, precipitación pluvial y pH. La distribución vertical de la biomasa fitoplanctónica estuvo directamente relacionada con la disponibilidad de luz en la columna de agua. No se encontraron diferencias espaciales ni temporales en la calidad del agua, seguramente porque los putos de muestreo eran cercanos y recibieron la misma carga de nutrientes provenientes del concentrado de los peces y de la excreción de estos mismos. La predominancia de cianobacterias a lo largo de todo el estudio seguramente fue debida a la influencia de los productos del alimento suministrado a los peces y sus excrementos que eutrifican el sistema. Temporalmente, el cambio en la estructura de las algas es explicado por la modificación de las condiciones físicas del agua entre superficie y fondo, provocado por el cambio en la dirección del viento con la consecuente alteración del fetch del agua.

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 30cm 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. Rev. Biol. Trop. 58 (4): 1421-1436. Epub 2010 December 01.

Los sistemas de lagos naturales constituyen reservorios importantes para el abastecimiento de agua residencial, la producción de peces, actividades recreativas y el disfrute de su belleza natural. Sin embargo, el impacto humano puede afectar su estado de salud como resultado de la degradación y la pérdida de biodiversidad. El objetivo del estudio fue determinar el estado de salud de un lago natural en una reserva indígena de la Amazonia brasileña, usando los cambios de la comunidad fitoplanctónica a lo largo de la época lluviosa (junio) y seca (de noviembre) en 2006. Se recogieron muestras de agua (temperatura, pH, conductividad y profundidad de Secchi) y fitoplancton del subsuelo, columna media del agua y a 30cm por encima del fondo, cada 24horas, en una estación central en el lago. Las variables bióticas y abióticas se correlacionaron mediante análisis de correspondencia canónica (CCA). Los resultados mostraron que el lago exhibió altas temperaturas en ambas temporadas, una estratificación térmica solamente durante la época lluviosa así como un patrón vertical de oxígeno disuelto, mientras que en la estación seca se observó una alta cantidad de oxígeno en el hipolimnion. En la época lluviosa, el agua cercana al fondo era ácida, turbia y tenía una mayor concentración de fósforo. Oxígeno disuelto, conductividad, pH, nitritos, fósforo total y disuelto mostraron variaciones diarias en la época lluviosa, mientras que la temperatura del agua, oxígeno disuelto, nitrógeno total y fósforo disuelto mostraron una diferencia significativa en las horas del día durante la estación seca. El fitoplancton estuvo representado por 39 táxones, y Chlorophyta mostró la mayor riqueza de especies, un total de 25 táxones. En Chlorophyta, los desmidios fueron los más diversos, lo que representa el 52%. Bacillariophyta (nueve especies) fue el segundo grupo más diverso. En Cyanophyta se encontraron tres especies, incluyendo Merismopedia tenuissima, el taxon más abundante. A pesar de la ocurrencia de taxones que indican contaminación orgánica, la biomasa y frecuencia sugieren que el sistema actualmente no está en peligro. Lago Caracaranã es un sistema oligotrófico, con baja densidad de algas y aislados episodios de afloramiento debido a su poca profundidad.

GEITLERINEMA SPECIES (OSCILLATORIALES, CYANOBACTERIA) REVEALED BY CELLULAR MORPHOLOGY, ULTRASTRUCTURE, AND DNA SEQUENCING(1).

Geitlerinema amphibium (C. Agardh ex Gomont) Anagn. and G. unigranulatum (Rama N. Singh) Komárek et M. T. P. Azevedo are morphologically close species with characteristics frequently overlapping. Ten strains of Geitlerinema (six of G. amphibium and four of G. unigranulatum) were analyzed by DNA sequencing and transmission electronic and optical microscopy. Among the investigated strains, the two species were not separated with respect to cellular dimensions, and cellular width was the most varying characteristic. The number and localization of granules, as well as other ultrastructural characteristics, did not provide a means to discriminate between the two species. The two species were not separated either by geography or environment. These results were further corroborated by the analysis of the cpcB-cpcA intergenic spacer (PC-IGS) sequences. Given the fact that morphology is very uniform, plus the coexistence of these populations in the same habitat, it would be nearly impossible to distinguish between them in nature. On the other hand, two of the analyzed strains were distinct from all others based on the PC-IGS sequences, in spite of their morphological similarity. PC-IGS sequences indicate that these two strains could be a different species of Geitlerinema. Using morphology, cell ultrastructure, and PC-IGS sequences, it is not possible to distinguish G. amphibium and G. unigranulatum. Therefore, they should be treated as one species, G. unigranulatum as a synonym of G. amphibium.