Population dynamics of pelagic rotifers in Marala Headworks (Pakistan) / Dinâmica populacional de rotíferos pelágicos em Marala Headworks (Paquistão)

Research work was designed to investigate the density and diversity of pelagic rotifers in a Lake near Marala Headworks. The physico-chemical parameters of water such as pH, dissolved oxygen, temperature, electrical conductivity, transparency and turbidity were evaluated. Correlation between rotifers and these parameters was also studied. Plankton sampling was done on monthly basis in order to check the population density of rotifers. In total, 18 species of rotifers were identified which belonged to 11 genera. The highest number of rotifers and their diversity was shown by genera namely Brachionus, Keratella, and Filinia. The Brachionus calyciflorus was dominant species in all the samples with mean population density (41%). Analysis of variance of physico-chemical parameters presented that the air and water temperature, electrical conductivity, transparency, dissolved oxygen and oxygen saturation were statistically significant in all the months. While pH was statistically non-significant (p≥0.05. Pearson correlation showed that oxygen and transparency were negatively correlated with rotifers density and diversity. Air and water temperature, concentration of hydrogen ions (pH), electrical conductivity and salinity showed positive relationship with density and diversity of rotifers.

O trabalho de pesquisa foi projetado para investigar a densidade e diversidade de rotíferos pelágicos em um lago perto de Marala Headworks. Foram avaliados os parâmetros físico-químicos da água como pH, oxigênio dissolvido, temperatura, condutividade elétrica, transparência e turbidez. A correlação entre rotíferos e esses parâmetros também foi estudada. A amostragem do plâncton foi realizada mensalmente para verificar a densidade populacional dos rotíferos. No total, foram identificadas 18 espécies de rotíferos pertencentes a 11 gêneros. O maior número de rotíferos e sua diversidade foi demonstrado pelos gêneros Brachionus, Keratella e Filinia. O Brachionus calyciflorus foi a espécie dominante em todas as amostras, com densidade populacional média (41%). A análise de variância dos parâmetros físico-químicos mostrou que a temperatura do ar e da água, condutividade elétrica, transparência, oxigênio dissolvido e saturação de oxigênio foram estatisticamente significantes em todos os meses. Enquanto o pH foi estatisticamente não significativo (p≥0,05), a correlação de Pearson mostrou que o oxigênio e a transparência foram negativamente correlacionados com a densidade e diversidade dos rotíferos. A temperatura do ar e da água, a concentração de íons de hidrogênio (pH), a condutividade elétrica e a salinidade mostraram relação positiva com a densidade e diversidade de rotíferos.

Experimental Studies on Zooplankton-Toxic Cyanobacteria Interactions: A Review.

Cyanobacterial blooms have been recognized as a problem in fresh water for about 150 years. Over the past 50 years, experimental studies on the subject have gained importance considering the increasing need to control toxic cyanobacterial blooms. This article presents information on the different lines of research that have been undertaken on zooplankton-cyanobacteria interactions over the past 50 years. These include information on filtering/ingestion rates and phytoplankton preferences of small and large rotifers, cladocerans, and copepods; growth rates of zooplankton on cyanobacterial diets; feeding rates of other freshwater invertebrates on cyanobacteria; role of zooplankton in top-down biomanipulation efforts; effect of cyanotoxins on zooplankton; bioaccumulation of cyanotoxins; and physical and chemical control of cyanobacterial blooms. We also highlight measures that have led to successful lake management and improvement of water quality in selected waterbodies.

Evaluation of the environmental impact of magnetic nanostructured materials at different trophic levels.

Safety on the use of magnetic nanomaterials (MNMs) has become an active topic of research given all the recent applications of these materials in various fields. It is known that the toxicity of MNMs depends on size, shape, and surface functionalization. In this study, we evaluate the biocompatibility with different aquatic organisms of engineered MNMs-CIT with excellent aqueous dispersion and long-term colloidal stability. Primary producers (the alga Pseudokirchneriella subcapitata), primary consumers (the rotifer Lecane papuana), and predators (the fish, Danio rerio) interacted with these materials in acute and sub-chronic toxicity tests. Our results indicate that P. subcaptita was the most sensitive taxon to MNMs-CIT. Inhibition of their population growth (IC50 = 22.84 mg L-1) elicited cell malformations and increased the content of photosynthetic pigments, likely due to inhibition of cell division (as demonstrated in AFM analysis). For L. papuana, the acute exposure to MNMs shows no significant mortality. However, adverse effects such as decreased rate of population and altered swimming patterns arise after chronic interaction with MNMs. For D. rerio organisms on early life stages, their exposure to MNMs results in delayed hatching of eggs, diminished survival of larvae, altered energy resources allocation (measured as the content of total carbohydrates, lipids, and protein), and increased glucose demand. As to our knowledge, this is the first study that includes three different trophic levels to assess the effect of MNMs in aquatic organisms; furthermore, we demonstrated that these MNMs pose hazards on aquatic food webs at low concentrations (few mgL-1).

Responses of the zooplankton community to the formation of a small reservoir on the Caveiras River, southern Brazil

We investigated changes in the species richness, abundance, and composition of the zooplankton community in response to the formation of a small reservoir in the Caveiras River, southern Brazil. Zooplankton were collected using a motor-pump and aplankton net (68 μm mesh), with 600 L of water filtered per sample. Sampling occurred during the pre-(April, August, and December 2011) and post-impoundment (July and October 2013, and January 2014) phases of the Caveiras River. We identified 86 taxa in this study, and rotifers were the predominant group. The species richness and abundance of the zooplankton increased after the filling of the reservoir. Furthermore, the zooplankton community showed a clear change in the species composition between the phases before and after the formation of the reservoir, with the emergence of typical planktonic species. Changes in the structure of the zooplankton community were related to changes in limnological characteristics due to the impoundment of the river, mainlyin the availability of food and in the concentration of nutrients.(AU)

Responses of the zooplankton community to the formation of a small reservoir on the Caveiras River, southern Brazil

We investigated changes in the species richness, abundance, and composition of the zooplankton community in response to the formation of a small reservoir in the Caveiras River, southern Brazil. Zooplankton were collected using a motor-pump and aplankton net (68 μm mesh), with 600 L of water filtered per sample. Sampling occurred during the pre-(April, August, and December 2011) and post-impoundment (July and October 2013, and January 2014) phases of the Caveiras River. We identified 86 taxa in this study, and rotifers were the predominant group. The species richness and abundance of the zooplankton increased after the filling of the reservoir. Furthermore, the zooplankton community showed a clear change in the species composition between the phases before and after the formation of the reservoir, with the emergence of typical planktonic species. Changes in the structure of the zooplankton community were related to changes in limnological characteristics due to the impoundment of the river, mainlyin the availability of food and in the concentration of nutrients.

Responses of stream zooplankton diversity metrics to eutrophication and temporal environmental variability in agricultural catchments.

Eutrophication of rivers and streams in agricultural lands is one of the main threats for biodiversity and ecosystem functions. This study was focused on seven subtropical streams where agriculture is the predominant land use. We tested the hypothesis that (i) eutrophication causes a decrease in taxonomic and functional diversity of zooplankton, leading to potential consequences for the ecosystem integrity. Furthermore, given that the temporal variability in the environmental conditions of each stream may influence the species sorting mechanisms, we also hypothesized that (ii) streams with higher temporal environmental variability have greater taxonomic and functional alpha (α) and temporal beta (ßt) diversity measures regardless of the trophic state. Thus, we characterized the streams according to their trophic state and analyzed the zooplankton composition, α and ßt by using taxonomic and functional perspectives. We found differences in the zooplankton composition between mesotrophic and eutrophic streams. However, eutrophic streams supported similar taxonomic and functional α diversity and similar taxonomic ßt diversity to mesotrophic ones. These results were mainly explained by the occurrence of rare species occupying different temporal niches in eutrophic systems. On the contrary, functional ßt diversity was lower in the eutrophic streams, being nestedness the ecological mechanisms underlying the variability in the zooplankton functional groups. Streams with higher temporal environmental variability supported greater α taxonomic diversity. However, the ßt diversity metrics showed no correlation with the environmental variability, suggesting that the environmental filters of the studied systems were the overriding determinants of species turnover. Our study suggests that both taxonomic and functional perspectives should be considered to improve our knowledge on the biotic responses to environmental changes. Also, among all metrics analyzed on the zooplankton community, functional ßt diversity was the most sensitive indicator of the eutrophication impact.

Rotifers from inland water bodies of continental Ecuador and Galápagos Islands: An updated checklist.

We present an updated checklist of the rotifer fauna from inland aquatic habitats in continental Ecuador and the Galápagos islands based on published rotifer records found in the literature. The checklist summarizes the status of the current taxonomic and faunistic knowledge on rotifers in Ecuador, updates the nomenclature, and reports the regions where each species has been found in the country. A total of 287 valid species (269 monogononts and 18 bdelloids was found. The Ecuadorian region with the highest number of records was Amazonia (228) followed by the Coastal region (139) and the Andes (121), whereas in the Galápagos Archipelago only 40 species have been recorded. Studies of the rotifer fauna of the areas are scarce and quite recent, pointing to important gaps in our knowledge on taxonomy and biogeography of Ecuadorian rotifers.

Effect of salinity and temperature on the acute and chronic toxicity of arsenic to the marine rotifers Proales similis and Brachionus ibericus.

Several abiotic factors influence the ecological responses of aquatic invertebrates to metal toxicity. We examined the effect of salinity (10, 20, and 30 psu) and temperature (25 and 32 °C) on acute and chronic arsenic (As) toxicity to the euryhaline rotifers, Proales similis and Brachionus ibericus. In general, higher salinities and low temperature resulted in lower arsenic toxicity. The population growth studies indicated that P. similis was more sensitive than B. ibericus to As. Arsenic toxicity intensified the vulnerability of P. similis to B. ibericus competition. Life table parameters decreased with increasing As levels in the medium. Chronic toxicity bioassays were more sensitive than acute toxicity tests for determining the adverse effect of As to rotifers. Our findings provide useful insights on the effect of arsenic on rotifer populations exposed to different temperature and salinity scenarios. Proales similis could be an important complement to brachionid rotifers for marine toxicity bioassays.

A long-term study on zooplankton in two contrasting cascade reservoirs (Iguaçu River, Brazil): effects of inter-annual, seasonal, and environmental factors.

BACKGROUND: In reservoirs, zooplankton strongly interact with the physical and chemical characteristics of water, and this interaction is mainly influenced by climate variation and the different methods used to manage the dam water level. Therefore, the aim of this study was to evaluate how the distinct operating modes of two cascade reservoirs affected the richness, abundance, and composition of zooplankton, both spatially (intra and inter-reservoirs) and temporally (annual and seasonal). In this study, the upstream reservoir (Salto Santiago) operates using the storage method, with a water retention time (WRT) of 51 days, whereas the downstream reservoir (Salto Osório) operates using the run-of-river method, with a WRT of 16 days. METHODS: Zooplankton samples were collected for 16 consecutive years from the two reservoirs located on the Iguaçu River, Brazil. A total of 720 samples were collected. Four-way ANOVAs were used to determine the differences in richness and abundance of the zooplankton among years, periods, reservoirs, and environments. Multidimensional non-metric scaling (NMDS) and an analysis of similarities (ANOSIM) were used to describe similarity patterns in species composition. Finally, a canonical correspondence analysis (CCA) was used to select the environmental predictors that best explained the variation in zooplankton abundance data. RESULTS: We identified a total of 115 taxa in this study, and rotifers were the richest group. In contrast, the copepods were the most abundant. The four-way ANOVA results showed significant differences in the species richness and abundance of the zooplankton among years, periods, reservoirs, and environments. The NMDS ordination and ANOSIM test indicated that the largest differences in zooplankton species composition were annual and seasonal differences. Finally, the CCA showed that these differences were mainly associated with changes in water transparency, temperature, and the chlorophyll a, phosphorus, and total dissolved solids concentrations. DISCUSSION: Inter-annual changes in zooplankton species composition showed that over time, large filters-feeders (e.g., large daphinids and calanoid copepods) were replaced by small cladocerans (e.g., bosminids) and generalist rotifers. The highest species richness was associated with the fluvial environment, whereas the highest abundance was associated with the transitional and lacustrine reservoir environments. Variations in water temperature, nutrients, and food availability explained the annual and seasonal changes in community structure, whereas variations in the water flow characteristics of the environments explained the longitudinal changes in the richness and abundance of zooplankton in reservoirs. The differences in zooplankton structure between the two reservoirs can be explained by the functional differences between the two systems, such as their WRTs and morphometrics.

Delivering Beneficial Microorganisms for Corals: Rotifers as Carriers of Probiotic Bacteria.

The use of Beneficial Microorganisms for Corals (BMCs) to increase the resistance of corals to environmental stress has proven to be effective in laboratory trials. Because direct inoculation of BMCs in larger tanks or in the field can be challenging, a delivery mechanism is needed for efficient transmission of the BMC consortium. Packaged delivery mechanisms have been successfully used to transmit probiotics to other organisms, including humans, lobsters, and fish. Here, we tested a method for utilizing rotifers of the species Brachionus plicatilis for delivery of BMCs to corals of the species Pocillopora damicornis. Epifluorescence microscopy combined with a live/dead cell staining assay was used to evaluate the viability of the BMCs and monitor their in vivo uptake by the rotifers. The rotifers efficiently ingested BMCs, which accumulated in the digestive system and on the body surface after 10 min of interaction. Scanning electron microscopy confirmed the adherence of BMCs to the rotifer surfaces. BMC-enriched rotifers were actively ingested by P. damicornis corals, indicating that this is a promising technique for administering coral probiotics in situ. Studies to track the delivery of probiotics through carriers such as B. plicatilis, and the provision or establishment of beneficial traits in corals are the next proof-of-concept research priorities.

Comunidades planctónicas y bacterianas asociadas al cultivo de bocachico Prochilodus magdalenae con tecnología biofloc / Describing the planktonic and bacterial communities associated with bocachico Prochilodus magdalenae fish culture with biofloc technology

RESUMEN Objetivo. Describir las comunidades planctónicas y bacterianas asociadas al cultivo de bocachico Prochilodus magdalenae con tecnología biofloc (BFT). Materiales y métodos. En nueve tanques rectangulares de concreto con volumen útil de 6.0 m3, se sembraron alevinos de bocachico con peso promedio de 1.6±0.2 g, a tres densidades 5 (T1), 10 (T2) y 20 (T3) peces/m3 con BFT, durante 120 días de cultivo. La identificación y cuantificación de los microorganismos se realizó cada ocho días, en una muestra de 250 ml de agua por tanque, mediante análisis de alícuotas en cámaras Sedgwick-Rafter y/o Neubauer bajo microscopio a 10x y 40x. Los días 15, 45 y 90 del cultivo se caracterizaron las comunidades bacterianas tomando una muestra de 2 g de floc en 90 ml de solución salina estéril y sometidas a pruebas microbiológicas convencionales. Resultados. Se identificarem cinco grupos planctónicos (microalgas, rotíferos, cladóceros, copépodos y protistas con predominancia de ciliados) con mayor cantidad de rotíferos y protistas en los cultivos con menor densidad (T1 y T2); y la mayor afluencia de microorganismos osciló entre 174.9±21.4 ind/ml (T1) y 125.6±16.1 ind/ml (T2). En el grupo de bacterias fue posible identificar 10 cepas: Escherichia coli, Enterobacter sp., Klebsiella sp., Salmonella sp. (Enterobacteriaceae) Bacillus subtilis, Bacillus sp, Lactobacillus sp, Pseduodomonas sp (Vibrionaceae), Micrococcus sp, Staphylococcus sp (Cocos gram+). Conclusiones. La composición del plancton fue similar en todos los tratamientos, con rotífero y protistas como los más abundantes; la mayor proporción de bacterias fueron Enterobacterias y Heterotróficas.

ABSTRACT Objective. To describe the planktonic communities and bacteria associated with the bocachico Prochilodus magdalenae fish culture with biofloc technology (BFT). Materials and methods. Bocachico fingerlings, with an average weight of 1.6±0.2 g, were stocked at three densities, i.e., 5 (T1), 10 (T2) and 20 (T3) fish/m3, with BFT in nine rectangular, 6.0 m3 concrete tanks for 120 days of culture. Identification and quantification of the microorganisms was performed every eight days in a sample of 250 ml of water per tank by analyzing aliquots on a Sedgwick-Rafter and/or in Neubauer chambers on a microscope at 10x and 40x magnification. On days 15, 45, and 90 of the fish culture, the bacterial communities were characterized by taking 2 g samples of floc and adding them to 90 ml of sterile saline solution, then subjecting them to conventional microbiological tests. Results. Five planktonic groups (microalgae, rotifers, cladocerans, copepods, and protists with ciliates predominating) with more rotifers and protists in the fish cultures at lower density (T1 and T2) were identified, and the largest amount of microorganisms oscillated between 174.9±21.4 ind/ml (T1) and 125.6±16.1 ind/ml (T2). It was possible to identify ten bacterial strains: Escherichia coli, Enterobacter sp., Klebsiella sp., Salmonella sp. (Enterobacteriaceae), Bacillus subtilis, Bacillus sp., Lactobacillus sp., Pseudomonas sp. (Vibrionaceae), Micrococcus sp., and Staphylococcus sp. (Coccus Gram+). Conclusions. The composition of plankton was similar in all treatments, with rotifers and protists being the most abundant; the bacteria showed a higher proportion of enterobacteria and heterotrophs.

Brachionus rotundiformis Tschugunoff, 1921 from the Brachionus plicatilis species complex (Rotifera: Monogononta): A new record from Galápagos Archipelago, Ecuador

The presence of the rotifer species Brachionus rotundiformis from the B. plicatilis species complex in Lake Arcturo, a saline lake in the Genovesa Island of the Galápagos Islands, is here reported. This is the first record of the species for the rotifer fauna of Ecuador as well as of the species complex to the Galápagos Islands. This finding is consistent with the idea of high dispersion capacity, and of cosmopolitan distribution of this species complex. Because Genovesa Island is uninhabited, passive transport by wind currents and zoochory by migrant birds seem to emerge as the most plausible factors in this process of colonization. Integrative studies on the morphological variations, genetic, molecular, and ecological aspects are still required to further understand the process of dispersion and the ecology of this member of the B. plicatilis species complex in this remote and isolated locality, and the exact taxonomical position of the islands population to the other members of the complex.(AU)

Brachionus rotundiformis Tschugunoff, 1921 from the Brachionus plicatilis species complex (Rotifera: Monogononta): A new record from Galápagos Archipelago, Ecuador

The presence of the rotifer species Brachionus rotundiformis from the B. plicatilis species complex in Lake Arcturo, a saline lake in the Genovesa Island of the Galápagos Islands, is here reported. This is the first record of the species for the rotifer fauna of Ecuador as well as of the species complex to the Galápagos Islands. This finding is consistent with the idea of high dispersion capacity, and of cosmopolitan distribution of this species complex. Because Genovesa Island is uninhabited, passive transport by wind currents and zoochory by migrant birds seem to emerge as the most plausible factors in this process of colonization. Integrative studies on the morphological variations, genetic, molecular, and ecological aspects are still required to further understand the process of dispersion and the ecology of this member of the B. plicatilis species complex in this remote and isolated locality, and the exact taxonomical position of the islands population to the other members of the complex.

Occurrence of concavities on the lorica of two species of Testudinella (Rotifera, Monogononta, Testudinellidae) / Ocorrência de concavidades na lórica de duas espécies de Testudinella (Rotifera, Monogononta, Testudinellidae)

Abstract: Testudinella is a taxon of Rotifera broadly distributed in Brazil. In a recent collection in marginal lakes connected to the Paranapanema River (São Paulo, Brazil), we found specimens of Testudinella mucronata and T. patina with concavities on their lorica. The objective of this study was to describe the concavities observed in individuals of both species and discuss their possible causes. Plankton samples were collected at two sampling stations, in the pelagic (PZ) and littoral (LZ) zones of the Panema and Coqueiral lakes; both of these lakes are ultra-oligotrophic and not polluted. For T. mucronata, 4% of individuals with concavities were found in the PZ of Coqueiral lake and 50% in the LZ of Panema lake. In T. patina, the proportion of specimens with concavities corresponded to 34% in the LZ of Panema lake and 17% in PZ of Coqueiral lake. In this study, we discussed that low water temperatures, predation events and/or recent hatching are factors that may justify the concavities in the lorica of specimens of our work.

Resumo: Testudinella é um táxon de Rotifera amplamente distribuído no Brasil. Em recentes coletas em lagos marginais conectados ao rio Paranapanema (São Paulo, Brasil), nós encontramos espécimes de Testudinella mucronata e T. patina com concavidades em suas lóricas. O objetivo do estudo foi descrever as concavidades observadas em indivíduos de ambas as espécies e discutir suas possíveis causas. Amostras de plâncton foram coletadas em duas estações de amostragem, na zona pelágica (PZ) e litorânea (LZ) dos lagos Panema e Coqueiral; ambos os lagos são ultra-oligotróficos e não poluídos. Para T. mucronata, 4% dos indivíduos com concavidades foram encontrados na PZ do lago Coqueiral e 50% na LZ do lago Panema. Em T. patina, a proporção de espécimes com concavidades correspondeu a 34% na LZ do lago Panema e 17% na PZ do lago Coqueiral. Nesse estudo, nós sugerimos que baixas temperaturas da água, eventos de predação e/ou recente eclosão são fatores que podem justificar as concavidades na lórica dos espécimes do nosso trabalho.

Dinámica de la dieta de Asplanchna girodi (De Guerne, 1888) en un embalse tropical, Colombia / The dynamics of the diet of Asplanchna girodi (De Guerne, 1888) inhabiting a tropical reservoir in Colombia / Dinâmica da dieta de Asplanchna girodi (De Guerne, 1888) em um reservatório tropical, Colômbia

Resumen Las interacciones bióticas como depredación, forrajeo y herbivoría han sido generalmente catalogadas como las fuerzas que determinan las variaciones espaciales y temporales de las poblaciones planctónicas, tanto de presas como de depredadores. Una especie del zooplancton, presente en aguas continentales, calificada como depredadora es el rotífero Asplanchna girodi. Sin embargo, se desconoce la composición real de su dieta, las preferencias alimentarias y la dinámica espacial y temporal en relación con sus presas o alimento. En esta investigación se determinaron las preferencias tróficas de A. girodi y su fluctuación espacio-temporal, basados en ítems verdaderamente consumidos en el medio natural, a través del análisis de los contenidos estomacales de individuos capturados en las aguas del embalse Riogrande II (Antioquia-Colombia), durante un año de muestreos realizados cada 10 días. Se observó que A. girodi presentó una preferencia trófica amplia que incluyó el forrajeo de, por lo menos, cinco taxones de algas y la depredación de ocho (8) especies de rotíferos y del cladócero Bosmina freyi. Se concluye que: 1. A. girodi es una especie omnívora, con mayor preferencia por el consumo de algas. 2. Este rotífero no fue factor de presión en la dinámica poblacional de las algas, pero posiblemente lo fue para Keratella americana. 3. No se observaron diferencias espaciales en la dieta de A. girodi, pero si existieron diferencias temporales en cuanto a la composición de la dieta, la cual estuvo determinada por la oferta de las algas, principalmente durante florecimientos de Ceratium. 4. Este tipo de dieta se enmarca dentro de los conceptos de forrajeo óptimo y oportunismo trófico, estrategias que conllevan el consumo de las especies con mayor disponibilidad (en este caso algas) y el máximo ahorro de energía, puesto que no se invierte en la búsqueda de presas específicas.

Abstract Biotic interactions such as predation, foraging and herbivory have been generally categorized as the forces that determine the spatial and temporal variations of planktonic populations, both preys and predators. A species of zooplankton, present in continental waters, classified as predator is the rotifer Asplanchna girodi. However, the true composition of its diet, dietary preferences and spatial and temporal dynamics in relation to its prey or food are unknown. In this research the trophic preferences of A. girodi and its spatio-temporal fluctuation were determined, based on items truly consumed in the natural environment, through analysis of stomach contents of individuals captured in the waters of Riogrande II reservoir (Antioquia-Colombia), during one year of sampling every 10 days. It was observed that A. girodi showed a broad trophic preference that included the foraging of, at least, five algae taxa and the predation of eight rotifer species and cladoceran Bosmina freyi. It is concluded that: 1. A. girodi is an omnivorous species, with a greater preference for the consumption of algae. 2. This rotifer was not a pressure factor in the population dynamics of the algae, but possibly it was for the Keratella americana. 3. No spatial differences were observed in the A. girodi diet, but there were temporal differences in the composition of the diet, which was determined by the algae supply, mainly during Ceratium blooms. 4. This type of diet is framed within the concepts of optimal foraging and trophic opportunism, strategies that involve the consumption of the most available species (in this case algae) and the maximum energy saving since it is not invested in the search for specific prey.

Resumo Interações bióticas como predação, forrageamento e herbivoria têm sido geralmente classificadas como as forças que determinam as variações espaciais e temporais de populações planctônicas, tanto de presas quanto de predadores. Uma espécie de zooplâncton, presente em águas continentais, classificada como predador é o rotífero Asplanchna girodi. No entanto, a composição real de sua dieta, preferências alimentares e dinâmicas espaciais e temporais em relação a suas presas ou alimentos são desconhecidas. Nesta pesquisa, as preferências tróficas de A. girodi e sua flutuação espaço-temporal foram determinadas, com base em itens verdadeiramente consumidos no ambiente natural, através da análise do conteúdo estomacal de indivíduos capturados nas águas do reservatório Riogrande II (Antioquia-Colômbia), durante um ano de amostragem a cada 10 dias. Observou-se que A. girodi apresentou uma ampla preferência trófica que incluiu o forrageamento de pelo menos cinco taxa de algas e a predação de oito (8) espécies de rotíferos e o cladocero Bosmina freyi. Conclui-se que: 1. A. girodi é uma espécie onívora, com maior preferência pelo consumo de algas. 2. Este rotífero não foi um fator de pressão na dinâmica populacional das algas, mas possivelmente foi para Keratella americana. 3. Não foram observadas diferenças espaciais na dieta de A. girodi, mas houve diferenças temporárias na composição da dieta, que foi determinado pelo fornecimento de algas, principalmente durante a floração de Ceratium. Este tipo de dieta enquadra-se nos conceitos de forrageamento ótimo e oportunismo trófico; estratégias que envolvem o consumo de espécies com maior disponibilidade (neste caso algas) e a máxima economia de energia, uma vez que não é investido na busca por presas específicas.

Mixture of commercial herbicides based on 2,4-D and glyphosate mixture can suppress the emergence of zooplankton from sediments.

It is generally assumed that zooplankton can recolonize lakes that have been exposed to pesticides, via their dormant egg banks. Hitherto, few studies have evaluated the relative importance of dormant egg bank recruitment in the re-establishment of zooplankton communities in the presence of pesticide. This study investigated the effects of commercial products Bratt® (a.i. 2,4-D), Roundup® (a.i. glyphosate) and their mixture on the emergence (abundance and taxon richness) of dormant zooplankton egg banks from natural lake sediment. Sediment samples were collected from the surface sediment (<10 cm depth) in four lakes in Southeast São Paulo, Brazil. We performed a hatching experiment, in which natural lake sediments containing dormant eggs were exposed separately to Bratt® (applied concentrations ranging from 0.30 to 20 mg L-1), Roundup® (0.28-8.5 mg L-1), and combined mixtures of all concentrations, plus one control (non-exposure to formulated herbicides) for a period of 28 days. All tested concentrations of Bratt®, Roundup® and their mixture reduced the abundance and taxon richness of emerging zooplankton (except 2 mg L-1 of Bratt®). This effect was more pronounced in rotifers. In comparison, there were no negative effects on the emergence of microcrustaceans. These findings suggest that commercial products Bratt®, Roundup® and their mixture can suppress the emergence of rotifers, thereby influencing zooplankton recruitment potential in lakes impacted by the presence of these commercial herbicides. Our results stress the importance of the need for additional studies to assess the effects of pesticides on dormant egg banks.

Combined effects of temperature and salinity on the demographic response of Proales similis (Beauchamp, 1907) and Brachionus plicatilis (Müller, 1786) (Rotifera) to mercury.

The demographic response of the brackish-water rotifers Proales similis and Brachionus plicatilis to mercury (0.5, 2, 8 and 32 µg L-1 of HgCl2) at different salinity levels (10 and 20‰) and two temperature (25 °C and 32 °C) regimes were evaluated. Median lethal concentration (LC50) for P. similis and B. plicatilis was 10 and 16 µg L-1, respectively, showing that Proales similis was more sensitive to mercury than B. plicatilis. The rate of population increase (r) for both species was greater at 10‰ salinity and 32 °C (ranged from 0.6 to 0.95 d-1). The r-value decreased as the concentration of mercury in the medium increased. Regardless of the temperature, at lower salinity and higher mercury concentration (32 µg L-1), P. similis died within six days. The survivorship of P. similis and B. plicatilis was higher at 25 °C than at 32 °C (ranged from 5 to 8 and 7-13 d, respectively). Fecundity was higher at 32 °C than at 25 °C for both rotifers species. There was a significant effect of the interaction among salinity, temperature, and mercury in both species on the reproductive variables such as net and gross reproductive rates, generation time and the rate of population increase. Considering the sensitivity of P. similis, we suggest that this species be included in the list of marine bioassay organisms.

Effect of crude extracts from cyanobacterial blooms in Lake Texcoco (Mexico) on the population growth of Brachionus calyciflorus (Rotifera).

Unlike temperate regions, tropical ecosystems are characterized by high temperatures (>18 °C) all year, promoting blooms of cyanobacteria which often produce secondary metabolites toxic to zooplankton. Nabor Carillo and the Recreational Lake are part of the saline, Lake Texcoco, in Central Mexico which is filled nowadays with treated waste water. Both water bodies are dominated by Planktothrix, Anabaenopsis, Spirulina and Microcystis. In this study we present the concentration of microcystins in these waterbodies over an annual cycle. We also evaluated the chronic effects of cyanobacterial crude extracts from both lakes on two clones of the rotifer Brachionus calyciflorus, one from Nabor Carrillo Lake and the other from a canal in the shallow, Lake Xochimilco. The experiments on population growth were performed, beginning with 10 individuals per container for each of the following treatments: control (no crude extract), concentrated crude extract, and diluted crude extract (50:50) with moderately hard water and Chlorella vulgaris in a concentration of 0.5 × 106 cells ml-1. The cyanotoxin levels were measured using an ELISA test and ranged between 0.20 and 2.4 µg L-1 in the lake water. The results showed that the Recreational Lake extracts were more toxic, killing the rotifers in less than five days. The r values ranged from -1.74 to 0.48 in the presence of the crude extracts and 0.16 and 0.24 in the controls. The results have been discussed with emphasis on the importance of conducting regular studies to test ecotoxicological impacts of cyanobacterial blooms in tropical waters.

Toxicity evaluation of cypermethrin, glyphosate, and malathion, on two indigenous zooplanktonic species.

In Aguascalientes, Mexico, there is a special concern about pesticides because of their intensive use on guava production areas, which are located in the vicinity of water reservoirs; thus, non-target organisms could be exposed. Thereafter, the aim of this work was to assess the effect of cypermethrin, Faena® (glyphosate), and malathion, which are the most used pesticides in Aguascalientes' guava production, on the indigenous freshwater species Alona guttata (cladoceran) and Lecane papuana (rotifer). Acute 48-h toxicity tests were carried out, and LC50 values were calculated. Then, five sublethal concentrations (1/80, 1/40, 1/20, 1/10, and 1/5 of the respective LC50) were selected for the chronic assays: (a) intrinsic growth rate analysis in the rotifer and (b) partial life table analysis in the cladoceran. The results of the acute toxicity tests showed that A. guttata was more sensitive to malathion (LC50 = 5.26 × 10-3 mg/L) at concentrations found in natural environments with continuous application on guava fields, whereas L. papuana was more sensitive to Faena® (LC50 = 19.89 mg/L). The somatic growth of A. guttata was inhibited for the chronic exposure to cypermethrin. In addition, cypermethrin and Faena® seemed to exert endocrine disruptive effects on A. guttata. Moreover, malathion chronic exposure significantly decreased the survival of A. guttata. Moreover, L. papuana was affected chronically for the three pesticides.

Performance of Debaryomyces hansenii as a Diet for Rotifers for Feeding Zebrafish Larvae.

The zebrafish larval stage is a critical moment due to high mortality rates associated with inadequate supplies of nutritional requirements. Larval feeding has important challenges associated with such factors as small mouth gape (≈100 µm), the low activity of digestive enzymes, and the intake of live food. A common zebrafish live food at the onset of exogenous feeding is rotifers, mainly Brachionus plicatilis. These rotifers should be fed with other microorganisms such as microalgae or yeast, mostly from the Saccharomyces genus. In the laboratory, the culture of microalgae is more expensive than the culture of yeast. The aim of this study was to evaluate the performance of Debaryomyces hansenii as a diet for rotifers in comparison to a microalgae-based diet (Rotigrow®). To achieve this aim, we assessed the rotifer total protein content, the rotifers fatty acid profile, zebrafish larval growth performance, the expression of key growth, and endocrine appetite regulation genes. The total protein and fatty acids content were similar in both rotifer cultures, averaging 35% of dry matter (DM) and 18% of DM, respectively. Interestingly, the fatty acids profile showed differences between the two rotifer cultures: omega-3 fatty acids were only observed in the Microalgae/rotifer, whereas, omega-6 fatty acids presented similar levels in both rotifer cultures. No differences were observed in the larval body length distribution or mortalities between the rotifer cultures. However, gh, igf-1, and cck gene expression showed significantly higher upregulation in zebrafish fed the Microalgae/rotifer diet compared with those fed the Debaryomyces/rotifer diet. In conclusion, D. hansenii could be an alternative diet for rotifer used as a live food in zebrafish larvae at the onset of exogenous feeding. The gene responses observed in this work open up the opportunity to study the effect of omega-3 supply on growth regulation in zebrafish.