ABSTRACT:The relationship between the trophic state of 39 reservoirs located in the semi-arid region of north-east Brazil and their planktonic structure was examined by a sampling survey during the 1998 drought (September to November). A total of 30 environmental and biological parameters, with special attention paid to phytoplankton, were studied once at each reservoir to obtain a synoptic view at a state scale (Pernambuco State). The application of the chlorophyll a-total phosphorus standard relationship for grades of eutrophication revealed a classification in which 90% of the sites were eutrophic-hypertrophic. Among the 202 taxa identified in the phytoplankton assemblages, the cyanobacterium Cylindrospermopsis (Wolsz.) Seenayya et Subba Raju represented more than 80% of the total phytoplankton density in 10 reservoirs and more than 50% in 17 reservoirs. The rarity of other phytoplanktonic groups in the case of the Cylindrospermopsis dominance is the most significant biological feature of these reservoirs. Although rotifers were more closely linked to hypereutrophic conditions than copepods or cladocerans, this dominant group did not seem to play an efficient role in cyanobacterial control. A statistical approach based on the analysis of cross tables (co-inertia analysis) allows us to describe species-environment relationships with a special focus on the factors governing the presence of Cylindrospermopsis. As determined by hierarchical analysis, a major group of studied reservoirs (70%) corresponded to deeper, warmer and hypertrophic reservoirs characterized by the combination of (1) low ammonia concentration, high temperature and pH values, and (2) high percentages of Cylindrospermopsis abundances. Lack of water renewal in 1998 linked to the 1997 El Niño consequences seems to be a major determinant for both trophic conditions and Cylindrospermopsis dominance in the reservoirs studied.KEY WORDS: Bacteria · Phytoplankton · Zooplankton · Cylindrospermopsis · El Niño event · Reservoirs · Co-inertia analysis Resale or republication not permitted without written consent of the publisherAquat Microb Ecol 23: [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] 2000 Cyanobacteria are recognized as a critical problem worldwide and their blooms are typical phenomena in eutrophic lakes, often linked to external nutrient enrichment (Paerl 1988). The influence of local climatological factors (e.g. wind, light intensity, temperature) can accelerate these phenomena and modify the phytoplankton structure, as cyanobacteria are strongly driven by physical factors such as local weather conditions (e.g. Tóth & Padisák 1986, Fabbro & Duivenvoorden 1996. Other factors that potentially influence the biomass and composition of phytoplankton include a stable water column with a turbulence limitation defined as a high ratio between the mixing zone and the euphotic zone (Soranno 1997). In addition, cyanobacteria are inedible prey for many zooplankton organisms because of their large colony size, their toxic effects and low...

-(Inter-annual variations in the floristic and population structure of an herbaceous community of "caatinga" in Pernambuco, Brazil). The influence of climatic variations on the herbaceous component of the "caatinga" vegetation was examined in the state of Pernambuco, Brazil. A total of 105 1 × 1 m-plots were established, of which 35 were in a level micro-habitat, 35 in a riparian micro-habitat, and 35 in a stony microhabitat. During two consecutive years all herbaceous plants in these plots were counted, measured (height and diameter), and collected for identification. The Shannon-Wiener diversity index and the equitability were calculated for each year, as well as the density, frequency, dominance, total basal area and importance index for each species. The total annual pluviometric was 819.5 and 448.8 mm in 2002 and 2003, respectively. The herbaceous flora in the study area was composed of 71 species, of which 58 were sampled in the plots. The families with the greatest species richness were Malvaceae (8 species), Euphorbiaceae (7), Poaceae (6), Convolvulaceae (4), Fabaceae (4), and Portulacaceae (4). The diversity indices were 2.66 and 3.01 nats ind -1 in 2002 and 2003, respectively. The density, frequency, dominance and importance value of herbaceous populations, as well as, the height and diameter of plants were low in the dryer year. The riparian group was the most isolated of the microhabitats examined, both in terms of its floristic and its population structure. Annual seasonal climatic variations greatly modified these populations structure during the course of this study, emphasizing the fact that longterm studies are needed in order to better understand the dynamics of the herbaceous component of the "caatinga" vegetation.Key words -"caatinga", herbaceous component, phytosociology, seasonal climate changes, species richness RESUMO -(Variações interanuais na composição florística e estrutura das populações de uma comunidade herbácea da caatinga, Pernambuco, Brasil). Objetivou-se avaliar a influência das variações climáticas sobre o componente herbáceo em uma área de caatinga de Pernambuco. Foram estabelecidas 105 parcelas de 1 × 1 m, sendo 35 dispostas em micro-habitat plano, 35 em micro-habitat ciliar e 35 em micro-habitat rochoso. Durante dois anos consecutivos todas as ervas presentes nas parcelas foram contadas, medidas (altura e diâmetro) e coletadas para identificação taxonômica. Foram calculados o índice de diversidade Shannon-Wiener, a equabilidade e os parâmetros de densidade, freqüência, dominância, área basal total e índice de valor de importância. A precipitação pluviométrica anual registrada foi de 819,5 e 448,8 mm em 2002 e 2003, respectivamente. A flora herbácea registrada nas parcelas e fora delas foi representada por 71 espécies, sendo 58 amostradas. As famílias de maior riqueza de espécies foram Malvaceae (8), Euphorbiaceae (7), Poaceae (6), Convolvulaceae (4), Fabaceae (4) e Portulacaceae (4). As diversidades foram de 2,66 e 3,01 nats ind -1 em 2002 e 2003, respectivamente. ...

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Brazil has a history of blooms and contamination of freshwater systems by cyanobacterial toxins. The monitoring relevance of toxins from cyanobacteria in reservoirs for public supply is notorious given its high toxicity to mammals, included humans beings. The most recurrent toxins in Brazilian water bodies are microcystins (MC). However, the recent record of cylindrospermopsin (CyN) in northeastern Brazil, Pernambuco state, alerts us to the possibility that this could be escalating. This study reports occurrence of MC and CYN, quantified with ELISA, in 10 reservoirs, devoted to public drinking supply in northeastern Brazil. The composition and quantification of the cyanobacteria community associated with these water bodies is also presented. From 23 samples investigated for the presence of MC, and CyN, 22 and 8 out were positive, respectively. Considering the similarity of the cyanobacteria communities found in reservoirs from Pernambuco, including toxin-producing species associated to MC and CyN, we suggest that geographic spreading can be favored by these factors. These issues emphasize the need for increased monitoring of MC and CyN in drinking supply reservoirs in Brazil.

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