Odete Rocha

Zooplankton community structure of two marginal lakes of the River Cuiabá (Mato Grosso, Brazil) with analysis of Rotifera and Cladocera diversity

In the present study, two small lakes on the margins of the River Cuiabá were analyzed regarding taxonomic composition and population densities of the zooplankton. Diversity was evaluated for two groups, Rotifera and Cladocera; sampling was carried out on two dates: 2 March 1999, in the rainy season, and 25 August 1999, in the dry season. Seventy-nine rotifer taxa, 30 cladoceran taxa, and 6 copepod taxa were found. Comparing the species identified in the present study with those recorded by other authors for several water bodies in Mato Grosso and Mato Grosso do Sul states, it was found that 9 species of Cladocera, 2 of Copepoda, and 14 of Rotifera are new records for the region. The most abundant rotifer species were Keratella cochlearis, Brachionus angularis, Polyarthra vulgaris, and Keratella americana. Moina minuta and Bosminopsis deitersi were dominant among the cladocerans, and Notodiaptomus transitans and N. devoyorum among the copepods. Comparing both lakes, the greatest species richness of both Rotifera and Cladocera was observed in Lake Souza Lima, during the rainy season. This is probably linked to the fact that the littoral region of this lake is densely colonized by macrophytes. The lake also has better environmental conditions since it does not receive domestic sewage inputs, as does Lake Parque Atalaia. The diversity of the Rotifera was markedly low in Lake Parque Atalaia, during the dry season, again perhaps linked domestic sewage input found in this water body.

Biodiversity assessment of benthic macroinvertebrates along a reservoir cascade in the lower São Francisco river (northeastern Brazil)

In order to verify the cascade-system effect in benthic macroinvertebrate communities, and the implications for policy making and proposals for conservation and sustainable use of the lower portion of São Francisco river basin (Bahia State, Brazil), a three-reservoir cascade system including two stretches downstream were studied during dry (June, 1997) and rainy (March, 1998) periods. The dominant groups found were Mollusca (Melanoides tuberculata), Oligochaeta, and Chironomidae larvae. Low Shannon-Wiener and Pielou index values were found, but with no significant difference between the sampling periods. However, density and taxonomic richness were significantly different (t(0.05: 31)) = -2.1945; p < 0.05; e t(0.05; 31) = -3.0600; p < 0.01) between the sampling periods, with a reduction in the number of taxa and macroinvertebrate abundance during the rainy period. An increasing gradient in benthic macroinvertebrate community structures was noted along the reservoir cascade from the first reservoir (Apolônio Sales), followed by a decrease downstream from the third reservoir of the system (Xing6). Despite the negative consequences of rapid proliferation of dams, which have caused widespread loss of freshwater habitats, the reservoir cascade system promoted an increase in benthic macroinvertebrate diversity, due to water-quality improvement along the system.

Phytoplankton community and physical-chemical characteristics of water in the public reservoir of Cruzeta, RN, Brazil

The Phytoplankton community and the abiotic factors of the Cruzeta reservoir were studied at three depths, surface, middle (2 m) and bottom, from September, 2004 to June, 2005, in order to characterize the environment and assess the possible factors that influence the compositional change of phytoplankton. Ninety species belonging to 6 classes (Chlorophyceae, Bacillariophyceae, Cyanophyceae, Dinophyceae, Chrysophyceae and Euglenophyceae) were identified with 66 and 80 taxonomic units in the dry and rainy season. The most representative class in terms of species richness was Chlorophyceae and dominated by Scendesmus quadricauda, Oocystis sp. and Chlorella sp. The group cyanobacteria were represented by 18 species of diverse morphological characteristics and the dominance of Cylindrospermopsis raciborskii in September 2004. The other major group, Bacillariophyceae is represented by 21 species with the predominance of Aulacoseira granulata in mid-column and bottom waters. The other dominant species was Phacus acuminatus of Euglenophyceae. The species diversity and evenness indices were high, moderate and low in relation to the three hydroperiod registered during the 2004-2005 annual cycle. The reservoir exhibits high electrical conductivity (290-550 microS x cm-1), alkaline pH (7.3-9.4), mean temperature of 28 degrees C, varying concentrations of dissolved oxygen (3.29-7.6 mg x L-l) and the greatest concentration of nutrients at the bottom (orthophosphate, 0.22-0.62 mg x L-1) with the general tendency of oligo-mesotrophic status during sampling periods. The chlorophyll a fluctuated to a minimum of 1.34 microg x L-l at the bottom in April, 2005 and a maximum of 14.3 microg x L-l in mid-column water in September, 2004. The reservoir is characteristically an oligo-mesotrophic environment.

Limnological and ecotoxicological studies in the cascade of reservoirs in the Tietê river (São Paulo, Brazil)

An evaluation was made of the quality of samples of water and sediment collected from a series of reservoirs in the Tietê River (SP), based on limnological and ecotoxicological analyses. The samples were collected during two periods (Feb and Jul 2000) from 15 sampling stations. Acute toxicity bioassays were performed using the test organism Daphnia similis, while chronic bioassays were carried out with Ceriodaphnia dubia and Danio rerio larvae. The water samples were analyzed for total nutrients, total suspended matter and total cadmium, chromium, copper and zinc concentrations, while the sediment samples were examined for organic matter, granulometry and potentially bioavailable metals (cadmium, chromium, copper and zinc). The results obtained for the limnological variable, revealed differences in the water quality, with high contribution of nutrients and metals for Tietê and Piracicaba rivers, besides the incorporation and sedimentation, consequently causing a reduction of materials in Barra Bonita reservoir, thus promoting the improvement of the water quality in the other reservoirs. The toxicity bioassays revealed acute toxicity for Daphnia similis only in the reservoirs located below Barra Bonita dam. On the other hand, chronic toxicity for Ceriodaphnia dubia and acute for Danio rerio showed a different pattern, decreasing in magnitude from Barra Bonita to Três Irmãos, demonstrating an environmental degradation gradient in the reservoirs.

Aerobic and anaerobic metabolism for the zebrafish, Danio rerio, reared under normoxic and hypoxic conditions and exposed to acute hypoxia during development

In order to verify the influence of chronic and acute ambient oxygen levels from egg to adult stage of the zebrafish, in vivo oxygen consumption (MO2), critical tensions of oxygen (Pcrit), heart rate (fH) and total body lactate concentration (Lc) were determined for Danio rerio (Hamilton, 1822) raised at 28 degrees C under normoxic (7.5 mgO2.L-1 or 80 mm.Hg-1) and hypoxic conditions (4.3 mgO2.L-1) and exposed to acute hypoxia during different developmental stages. Our findings confirmed that very early stages do not respond effectively to ambient acute hypoxia. However, after the stage corresponding to the age of 30 days, D. rerio was able to respond to acute hypoxia through effective physiological mechanisms involving aerobic and anaerobic metabolism. Such responses were more efficient for the fishes reared under hypoxia which showed that D. rerio survival capability increased during acclimation to mild hypoxia. Measurements of body mass and length showed that moderate hypoxia did not affect growth significantly until the fish reached the stage of 60 days. Moreover, a growth delay was verified for the hypoxic-reared animals. Also, the D. rerio eggs-to-larvae survival varied from 87.7 to 62.4% in animals reared under normoxia and mild hypoxia, respectively. However, the surviving animals raised under moderated hypoxia showed a better aptitude to regulate aerobic and anaerobic capacities when exposed to acute hypoxia.

Alterations on growth and gill morphology of Danio rerio (Pisces, Ciprinidae) exposed to the toxic sediments

The objective of this work was to assess the toxicity of sediment samples from six cascade reservoirs in Tiete river system, in Sao Paulo State, Brazil, through chronic-partial toxicity bioassays with Danio rerio larvae as test-organisms. Histology of gills and biometric measurements were used to determine the existence of toxicity problems. The alterations on gill morphology here detected were considered of first stage (hyperplasia, lamellar junction and excess of mucous cells) in the first reservoirs and very slight in the last ones. The biometric analysis pointed to inadequate conditions for the growth of the test-organisms when exposed to the sediment of the rivers and upstream reservoirs and also indicated an improvement of environmental conditions along the system.

Acute Toxicity Tests with the Tropical Cladoceran Pseudosida ramosa: The Importance of Using Native Species as Test Organisms

Cladocerans have long been used for toxicological assessments of a diverse range of substances. The use of cladocerans in toxicity tests has many advantages, such as their short life cycle, parthenogenetic reproduction (clones), and high sensitivity to toxicants, as well as the easy laboratory maintenance of cultures. The most commonly used cladoceran in ecotoxicological studies of aquatic environments is undoubtedly Daphnia magna. Standard methods using cladocerans as test organisms have been documented and adopted by major international organizations and regulatory agencies of many countries. However, today there is a growing need for improving test organisms and protocols to better reflect local species sensitivity or site-specific conditions. The present study aimed to assess the tropical species Pseudosida ramosa as a potential test organism for ecotoxicological purposes, by carrying out standard acute tests with six reference compounds. Based on the results obtained in the present study and in comparison with other cladocerans, it was found that P. ramosa was more sensitive than Daphnia magna, had a sensitivity similar to that of Daphnia similis, and was less sensitive compared to Ceriodaphnia dubia and C. silvestrii (Neotropical species), except for the salts, sodium chloride and potassium chloride. Also, when P. ramosa was compared with test organisms of other taxonomic groups, we observed that it was more sensitive than most of the others, from simple coelenterates to complex fish. Considering these results and the wide distribution of the cladoceran P. ramosa in tropical and subtropical regions, we suggest that this species can be adopted as a test organism, being a good substitute for the exotic daphnid D. magna, for monitoring of toxicants in freshwaters.

Phytoplankton community: indicator of water quality in the Armando Ribeiro Gonçalves Reservoir and Pataxó Channel, Rio Grande do Norte, Brazil

The current study analysed spatial-temporal modifications of the phytoplankton community and water quality, during dry and wet seasons. The phytoplankton community was studied in three areas: Armando Ribeiro Gonçalves Reservoir (ARG), which is an important public use reservoir in RN, Pataxó Channel (PC-before water treatment), Itajá, RN, and after the water treatment (WTP). Water samples from the reservoir were collected during both dry (January, February and November, 2006) and wet seasons (March to June, 2006). Quali-quantitative analyses of phytoplankton were carried out. Results indicated a qualitative similarity of the phytoplankton community in the three areas. However, significant differences were registered in these areas in relation to species relative abundance, with dominance of potentially toxic cyanobacteria, such as Planktothrix agardhii Gomont (dry season) and Microcystis aeruginosa Kutz (wet season). Ecological indexes obtained higher values before water treatment. Nevertheless, densities of cyanobacteria (organisms/mL) gradually reduced in the waters of the reservoir and of the Pataxó Channel before and after water treatment. After the treatment, density values of cyanobacteria were adequate for human consumption, according to the values established by the Health Ministry.

Predation on Ceriodaphnia cornuta and Brachionus calyciflorus by two Mesocyclops species coexisting in Barra Bonita reservoir (SP, Brazil)

Feeding experiments with two species of carnivorous copepod, Mesocyclops longisetus (Thiebaud) and Mesocyclops kieferi Van de Velde from Barra Bonita, a eutrophic reservoir in São Paulo, Brasil, were performed using two common types of prey: Ceriodaphnia cornuta, a cladoceran, with a mean body length of 464 µm (including spines) or 393 µm (without spines), and Brachionus calyciflorus, a rotifer with a mean body length of 350 µm (including spines) or 279 µm (without spines).Both species showed higher consumption rates on Brachionus than on Ceriodaphnia. For Mesocyclops longisetus, the average rates were: 2.19 prey ind−1 h−1 (Brachionus), and 1.30 prey ind−1 h−1 (Ceriodaphnia). For Mesocyclops kieferi, the rates were 1.85 prey ind−1 h−1 (Brachionus) and 0.60 prey ind−1 h−1 (Ceriodaphnia). These experimental data are discussed with reference to the dynamics of the predator and prey populations in the reservoir.

Denitrification and bacterial community structure in the cascade of six reservoirs on a tropical river in Brazil

Denitrification activity was measured by the acetylene blockage technique in six reservoirs of the Tietê River, southeastern Brazil, in March 1999 and July 1999. The total number of bacteria was measured by DAPI while bacterial community structures were estimated with fluorescent in situ hybridization (FISH) using oligonucleotide probes specific to ribosomal RNA of the domain Bacteria; the alpha, beta and gamma subclasses of the Class Proteobacteria; the Cytophaga-Flavobacterium group; the Order Planktomycetales; and the Domain Archaea. Denitrification was detected only where anoxia or low concentrations of dissolved oxygen were observed. Maximum in situ denitrification integrated in the water column ranged from 1.36 to 3.79 mmol-N2O m−2 day−1 in the rainy season and in the dry season, respectively, both at Station 1, the upstream portion of Barra Bonita Reservoir influenced by the sewage carried out by the river from São Paulo City. Bacterioplankton community analysis by FISH showed that the Alpha subclass of the class Proteobacteria was the main subgroup in the middle and low Tietê River (Fig. 3), represented by 10.3–19.2% of total, followed by the Beta Subclass of Proteobacteria and the Cytophaga/Flavobacterium group, represented by 8.3–13.3% and 3.4–10.9%, respectively). This result differs from the proportion of bacterial subgroups in water bodies of temperate regions, suggesting that bacterial communities of water bodies of the tropical region may differ from those of temperate regions.