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Cladocerans are a diverse group of species that show rapid responses to changes in environmental conditions. This adaptive capacity has important implications for egg production and life cycle, especially in transitory environments such as temporary waterbodies. The present study investigated the life history and egg production of Alona gutatta Sars, 1862 (Crustacea, Cladocera), an abundant and frequent species from a high-altitude temporary pond (Lagoa Seca, Minas Gerais, Brazil). Newly hatched neonates were monitored in relation to time of maturation, number of eggs produced per female and time of survival. Neonates required a mean of 8 days to mature. A. guttata survived for a mean of 30.9 ± 8.1 days and produced 2 eggs per brood, generating a mean of 10.95 ± 6.41 neonates during the entire life cycle. The rapid development, short time to produce eggs and long life cycle are important adaptations to the adverse environmental conditions of temporary aquatic environments, which can contribute to the rapid colonization of Alona guttata in transitory ecosystems.

The main objective of the present study was to promote some adaptations to the standard methodology used in the analysis of Cladocera subfossils. The samples used in this study were collected at Lagoa dos Coutos, a temporary lake located on an outcrop with iron-rich duricrust in the Serra do Gandarela (Minas Gerais, Brazil). The sediment from this pond, typical of temporary ecosystems in the region, is characterized by rigid concretions that are difficult to dissolve in aqueous media, making it difficult to visualize and analyze subfossils taxa. Sediment samples were prepared according to the standard methodology used in paleolimological studies and the methodological adaptations proposed in the present study, which included the addition of 1 mg of Kochia scoparia, a palynological marker used to estimate subfossil density, as well as the addition of hydrofluoric acid (HF) to oxidize silicate materials. The samples prepared according to the new methodological procedure improved Cladocera subfossil visualization, facilitating the taxonomic analysis of the species. The samples submitted to the standard methodological procedure had a significantly higher mean of sediment particles (mean of 84.2 sediment particles) and 70% more residues compared to the samples prepared with the newly proposed methodology (mean of 22.1 sediment particles). Absolute data on the temporal variation of the density of Cladocera subfossils was obtained by using the palinological marker K. scoparia, which showed higher densities of subfossils in more recent, humid periods (112,000 subfossils/cm3 at 5 cm, equivalent to 3,500 years BP). The results indicate that the new methodology can contribute to advances in paleolimnological studies of temporary aquatic ecosystems, whose lake histories are rarely investigated, despite their ecological relevance as ecosystems that indicate environmental and climatic changes.

The aim of our study was to assess whether cyanotoxins (microcystins) can affect the composition of the zooplankton community, leading to domination of microzooplankton forms (protozoans and rotifers). Temporal variations in concentrations of microcystins and zooplankton biomass were analyzed in three eutrophic reservoirs in the semi-arid northeast region of Brazil. The concentration of microcystins in water proved to be correlated with the cyanobacterial biovolume, indicating the contributions from colonial forms such as Microcystis in the production of cyanotoxins. At the community level, the total biomass of zooplankton was not correlated with the concentration of microcystin (r2 = 0.00; P > 0.001), but in a population-level analysis, the biomass of rotifers and cladocerans showed a weak positive correlation. Cyclopoid copepods, which are considered to be relatively inefficient in ingesting cyanobacteria, were negatively correlated (r2 = - 0.01; P > 0.01) with the concentration of cyanotoxins. Surprisingly, the biomass of calanoid copepods was positively correlated with the microcystin concentration (r2 = 0.44; P > 0.001). The results indicate that allelopathic control mechanisms (negative effects of microcystin on zooplankton biomass) do not seem to substantially affect the composition of mesozooplankton, which showed a constant and high biomass compared to the microzooplankton (rotifers). These results may be important to better understand the trophic interactions between zooplankton and cyanobacteria and the potential effects of allelopathic compounds on zooplankton.

This study analyzed the presence of Biomphalaria in Melo creek basin, Minas Gerais state, and its relationship to irrigation canals. Seventeen of these canals were used to determine a limnological, morphological and hydrological characterization during an annual seasonal cycle. Biomphalaria samples were sent to René Rachou Research Center/FIOCRUZ for identification and parasitological examination. Six canals were identified as breeding areas for mollusks and in one of them it was registered the coexistence of B. tenagophila (first report to this basin) and B. glabrata species. Results indicated that the low flow rate and speed of water flow were the main characteristics that contributed to this specific growth of the mollusks in the area. These hydraulic characteristics were created due to anthropogenic action through the canalization of lotic areas in Melo creek, which allowed ideal ecological conditions to Biomphalaria outbreak. The results emphasize the need of adequate handling and constant monitoring of the hydrographic basin, subject to inadequate phytosanitary conditions, aiming to prevent the occurrence and propagation of schistosomiasis.

Dinoflagellates of the genus Ceratium are generally marine organisms, but rare occurrences in freshwater have been observed in Brazil. In this paper we are recording for the first time the presence of Ceratium furcoides, an invasive species, in a shallow, natural intermittent pool formed at a high-altitude at the southern end of the Iron Quadrangle, an iron-mining district of Minas Gerais State (Southeast Brazil). Samples were collected in October and November of 2010 (rainy period). The population density of this organism observed in Lagoa Seca ("Dry Pool") was very low, at most 4 ind L-1. Mountain lakes are extremely vulnerable to atmospheric deposition of organisms, making them valuable witnesses both of the many forms of impact arising from human activities and of the extended global connections that facilitate the dispersion and introduction of new species over great distances. Studies on the population dynamics of C. furcoides in natural tropical systems are still rare and very recent to the brazilian scenario and hence the monitoring of its dynamics and the potential impact on aquatic communities of its becoming established are essential to an understanding of the process of bioinvasion by this species.

Species composition, density, and temporal dynamics of zooplankton were studied in six reservoirs in a semi-arid region in tropical northeastern Brazil (Rio Grande do Norte state). All the reservoirs are highly eutrophic, with high contents of total nitrogen (minimum of 1200 µg.L(-1)) and total phosphorus (minimum of 10 µg.L(-1)), and extremely high algal biomass was registered (surpassing 20 µg Chl a.L(-1)). All the reservoirs showed an enduring condition of high turbidity and phytoplankton assemblages dominated by cyanobacteria. Zooplankton also showed quantitative patterns suggestive of eutrophic conditions, expressed by high densities, mainly in Passagem das Traíras and Sabugi reservoirs. A spatial differentiation in the composition of the zooplankton community was registered. Rotifers (especially Keratella tropica, Brachionus havanensis, and Keratella americana) were the dominant forms in the zooplankton community of Itans, Passagem das Traíras, and Sabugi reservoirs, while calanoid copepods (mainly Notodiaptomus cearensis) dominated in the Armando Ribeiro, Gargalheiras, and Parelhas systems. The existence of novel relationships in zooplankton community composition in eutrophic reservoirs in this tropical semi-arid region must be considered in designating zooplankton indicators of eutrophic conditions.

Guaraíras Lagoon is a shallow coastal lagoon subject to intense human impacts, including shrimp aquaculture, urban expansion and agricultural activities, and is therefore vulnerable to eutrophication. With the aim of detecting the effects of human-mediated disturbance and environmental change in the lagoon, a spatial-temporal study was conducted in order to assess the actual ecological status of the lagoon and the species composition and density of the mesozooplankton, highlighting copepod assemblages. Algal biomass (chlorophyll-a) and total phosphorus concentration indicated that the lagoon is a meso-eutrophic coastal system in the inner part, and is oligotrophic in the areas influenced by the marine waters. High salinities were recorded in the lagoon, characterizing the lagoon as a coastal-marine ecosystem, rather than true estuarine. Mesozooplankton abundance fluctuated widely and showed marked spatial heterogeneity. The copepod assemblage was characterized by a coastal/estuarine group dominated by Oithona spp., Acartia lilljeborgi and Parvocalanus crassirostris in the inner areas of the lagoon, and a marine group characterized by the copepods Paracalanus quasimodo, Calanopia americana, Corycaeus (C.) speciosus and Monstrilloida in the area of marine influence. Thus, the spatial variability in the distribution of mesozooplankton species can be ascribed to the presence of a horizontal gradient of salinity and trophic conditions. Overall, the results showed that spatial variation in the water physicochemical characteristics of Guarairas Lagoon have significant effects on the structure and repartition of the mesozooplankton assemblages, which may potentially affect the functioning and biodiversity of this coastal ecosystem.

Fecal pellets produced by mesozooplanktonic copepods (Centropages velificatus and Paracalanus parvus) and macrozooplanktonic Euphausiacea (Euphausia sp.) were examined using scanning electron microscopy. Fragments of the protozoan Sticholonche zanclea were found in both copepod and in Euphausia sp. fecal pellets, even when the abundance of the protozoan in the water was low. The results suggest that S. zanclea is an important food resource for different trophic levels, including meso- and macrozooplankton, in Brazilian coastal waters.

The qualitative composition, numerical abundance and seasonal distribution of microzooplankton in the São Sebastião Channel were studied in different seasonal periods. Data are presented for 43 Protozoa, 4 rotifer and 30 copepod nauplii specimens. Tintinnids represented the most abundant group within the microzooplankton community, with 31 species recorded, among which Amphorellopsis acuta, Codonellopsis morchella, Eutintinnus tenuis, Favella ehrenbergii, Leprotintinnus nodqvisti, Tintinnopsis buetschlil, T. lobiancoi and T. radix stood out, followed in abundance by copepod nauplii. Our findings indicated that water masses play a fundamental role in the seasonal composition of microzooplankton assemblages in the São Sebastião Channel.

The aim of this study was to assess the major food items ingested by adult specimens of Daphnia laevis within the eutrophic Pampulha reservoir in Belo Horizonte, Minas Gerais, Brazil. The gut content was analyzed after addition of sodium hypochlorite and also through the examination of dissected guts under scanning electron microscopy. The results showed that Chlorophyceae was the main food item ingested, representing c. 80.5% of the total ingested food. Moreover, Eutetramorus fottii, Coelastrum pseudomicroporum and Oocystis lacustris, the dominant phytoplankton species within the reservoir, were the most frequent cells found in the gut contents. Euglenophyta also represented an important food item accounting for 15% of the ingested material, including mainly Trachelomonas volvocina and Euglena oxyuris, although less abundant in the reservoir (< 10% of total phytoplankton). Blue-green algae occurred at much lower percentages in the guts than in the phytoplankton. A small amount of undigested Microcystis aeruginosa colonies were also found in the gut content of D. laevis. Scanning electron microscopy results showed that, besides phytoplankton cells, a great amount of abiogenic material was also ingested. The amount of this inorganic material increased considerably in the tract (from 15% to 75% of the gut content), when a peak of D. laevis was observed in the reservoir. Our assumption is that the ingestion of this inorganic material can be a strategy used by D. laevis to obtain additional food supply.