Ivaneide Alves Soares da Costa

Zooplankton assemblages in eutrophic reservoirs of the Brazilian semi-arid

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.

Composition and abundance of zooplankton community of an impacted estuarine lagoon in Northeast Brazil

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.

Cyanobacterial occurrence and detection of microcystins and saxitoxins in reservoirs of the Brazilian semi-arid

Aim:The rapid spread of cyanobacteria in water sources and reservoirs has caused serious environmental damage and public health problems, and consists in a problem that challenges the institutions responsible for providing water to the population. In this study, the quantification of microcystin, saxitoxins and cyanobacteria levels was performed over 3 years in the semi-arid reservoirs of Rio Grande do Norte (Brazil). In addition, we analyzed the seasonal distribution of cyanotoxins and the percentage of cyanobacteria and cyanotoxins which were above the limit established by Brazilian law.MethodsThe study was conducted between 2009 and 2011 in four dams with six sites: Armando Ribeiro Goncalves (ARG) in Itaja, San Rafael (SR) and Jucurutu; Passagem das Trairas (PT); Itans and Gargalheiras (GARG). Cyanobacteria presence were quantified and identified and the presence of microcystins (MCYs) and saxitoxins (STXs) was investigated by ELISA.ResultsThe densities of cyanobacteria were found to be above the permitted in 76% of cases. The ELISA results showed that of the 128 samples analyzed, 27% were above the maximum allowed by the Brazilian Ministry of Health Order 2914/2011. A seasonal pattern for the presence of MCYs was found (0.00227 to 24.1954 µg.L–1), with the highest values in the rainy season. There was no clear seasonal pattern for STXs (0.003 to 0.766 µg.L–1).ConclusionsThis study showed the importance of establishing a water quality monitoring for human consumption and its potability standards since the concentration of MCYs in some samples was above the maximum limit allowed by Brazilian law, thus posing a risk to public health since the conventional water treatment is not able to eliminate these potent hepatotoxins.

Vertical and temporal dynamics of phytoplanktonic associations and the application of index assembly in tropical semi-arid eutrophic reservoir, northeastern Brazil

Objetivodeterminar a composicao e a biomassa dos grupos funcionais nos gradientes vertical e temporal, correlacionando com as condicoes ambientais e aplicar o indice Q num reservatorio usado para abastecimento humano.MetodosAmostras de agua foram coletadas mensalmente (n=92) entre 2009 e 2011, em dois pontos do reservatorio para analises fisicoquimicas e biologicas.ResultadosO pH, oxigenio dissolvido e temperatura da agua apresentaram diferencas significativas entre as zonas eufotica e afotica (p<0.05). A variacao vertical do de oxigenio dissolvido e temperatura da agua, mostrou um perfil de micro-estratificacao. A comunidade fitoplanctonica foi representada por 11 grupos funcionais: S1, M, H1, Lo, P, F, SN, J, W2, MP e R.ConclusoesVariacoes verticais foram menos pronunciadas do que as variacoes temporais na comunidade fitoplanctonica. O indice Q apontou ma qualidade da agua, que corresponde ao estado atual da eutrofizacao no reservatorio e foi sensivel a capacidade de resposta as mudancas ambientais e hidrodinâmicas do reservatorio, mostrando ser um instrumento adequado para monitoramento de reservatorios em regiao tropical semi-arido.

Can microcystins affect zooplankton structure community in tropical eutrophic reservoirs

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.

ZOOPLANKTON COMPOSITION IN EUTROPHIC RESERVOIRS OF THE SEMI-ARID REGION OF RIO GRANDE DO NORTE STATE (Northeast Brazil).

ZOOPLANKTON COMPOSITION IN EUTROPHIC RESERVOIRS OF THE SEMI-ARID REGION OF RIO GRANDE DO NORTE STATE (Northeast Brazil). Species composition and abundance of the zooplankton were studied in six eutrophic reservoirs of Rio Grande do Norte State, which showed high concentrations of total phosphorus, high phytoplankton biomass and dominance by cianobacteria. Sampling was carried out during dry, rainy and transitional periods. Zooplankton also showed quantitative patterns suggestive of eutrophic conditions, expressed by high densities. Moreover it was observed a spatial differentiation in the composition of zooplankton community. Rotifers (specially Keratella tropica, Brachionus havanensis e Keratella americana) were the dominant forms in the zooplanktonic community of Itans, Passagem das Traíras and Sabugi reservoirs, while Calanoid copepods (mainly Notodiaptomus cearensis) dominated in Armando Ribeiro, Gargalheiras and Parelhas reservoirs. The results obtained point out to new relationships in the composition of zooplanktonic community in eutrophic reservoirs of the tropical semi-arid, including the occurrence of large-sized herbivorous zooplankton such as Calanoid copepods, which must be considered in the establishment of zooplanktonic indicators of eutrophic conditions in reservoirs.