Longitudinal changes in composition, abundance, and distribution of copepods were studied at the transition zone of Paranapanema River-Jurumirim Reservoir (SP, Brazil). The interchange of biotic material between marginal lakes and the river system was also examined. Water samples were obtained from 6 stations along a stretch of 13 km of the Paranapanema River, from an upstream reach with high water velocity up to the river mouth into Jurumirim Reservoir. Two other sites in lateral lakes were also sampled. Nine copepod taxa were identified: 3 calanoids (Argyrodiaptomus furcatus Sars, Notodiaptomus iheringi Wright, and N. conifer Sars) and 6 cyclopoids (Eucyclops Claus, Microcyclops Claus, Mesocyclops longisetus Thiébaud, Thermocyclops decipiens Fischer, T. minutus Lowndes, and Paracyclops Claus). Harpacticoids were also collected. Calanoid and cyclopoid nauplii and copepodids, and harpacticoids were the most abundant organisms. In general, there was a longitudinal decrease in copepod abundance, whereas an increase was detected near the lakes. The abundance of most copepods was inversely correlated with current velocity and suspended solids. Higher abundance was observed in the river main course during the rainy season, during which there is a higher connectivity between the lakes and the main river. This promotes exportation of biologic material from marginal lakes to the river system, a biotic exchange reflecting the importance of marginal lakes to the river community structure.Key words: Copepoda, longitudinal distribution, river, lakes, floodplain. RESUMO Distribuição longitudinal de Copepoda na região de transição rio-reservatório (rio Paranapanema-Represa de Jurumirim, SP) e influência de duas lagoas lateraisO presente estudo foi realizado na zona de desembocadura do rio Paranapanema, na Represa de Jurumirim, visando a verificar as mudanças longitudinais na composição, abundância e distribuição dos Copepoda e a analisar a influência de lagoas laterais na exportação de material biótico para o rio. Foram amostrados 6 pontos no rio (trecho de 13 km), desde um local mais a montante, com alta velocidade da correnteza, até um local com características mais lênticas, na desembocadura do rio na represa, além de duas lagoas conectadas ao rio. Foram identificados 9 taxa: 3 Calanoida (Argyrodiaptomus furcatus Sars, Notodiaptomus iheringi Wright e N. conifer Sars) e 6 Cyclopoida (Eucyclops Claus, Microcyclops Claus, Mesocyclops longisetus Thiébaud, Thermocyclops decipiens Fischer, T. minutus Lowndes e Paracyclops Claus), além de representantes da ordem Harpacticoida. Braz. J. Biol., 64(1): 11-26, 2004 12 CASANOVA, S. M. C. and HENRY, R.Os organismos mais abundantes foram as fases de desenvolvimento nauplius e copepoditos, de Calanoida e Cyclopoida e os Harpacticoida. De forma geral, observou-se diminuição na abundância dos Copepoda, do ponto 1 ao ponto 5, aumentando, porém, no ponto 6 e nas lagoas marginais. A maioria dos Copepoda mostrou relação inversa com a velocidade da corrente e o material em suspensão...

Spatial and temporal variations on the primary productivity by the phytoplankton in Jurumirim Reservoir (Paranapanema River, São Paulo, Brazil)A study on the spatial and temporal variations of the primary productivity by phytoplankton was conducted in Jurumirim Reservoir (Paranapanema River, São Paulo, Brazil) from October, 1995 to July, 1996. Six sampling stations were selected, three in Paranapanema Arm, two in Taquari Arm and one in das Posses Arm. The C 14 method was used for measuring the primary production and a study on the correlated physical and chemical variables was made.In November, 1995 and in January-February, 1996 the T 2 station (transition region of Taquari Arm) presented the highest value of primary production (23.9 and 20.1 mgC.m , respectively) and in the other two studied periods (April and July, 1996), it was the second most productive station (6.0 and 10.2 mgC. .h -1 ), when compared with the other five stations. In Taquari Arm, an increase on the primary production occurred from the T 1 (riverine zone) to T 2 stations (transition region), in all the four studied periods. In Paranapanema Arm, an increase on the primary production was also observed from the P 1 (riverine zone) to P 2 (transition zone) and to P 3 stations (main water body zone) in October-November, 1995 and July, 1996. In January-February 1996, the increase in the three successive stations was low, while in April, 1996 no significant variation was observed on the primary production. A variance analysis showed that there were significant modifications in the suspended matter amounts, in the water conductivity and in the inorganic phosphate and nitrate concentrations in the different periods of the year.The seasonal variations can be attributed to the water precipitation, to the allochthonous loads of suspended solids, nitrogen and phosphorus introduced by the two tributaries, and to internal recycling of nutrients. The statistical analysis also showed significant differences between sampling stations on the primary productivity by phytoplankton, on the euphotic zones, on the water conductivity and on the silicate concentrations. The spatial differences of the primary productivity are due to the modifications on the amplitudes of the euphotic zones. The euphotic layer presents longitudinal variations, that can be attributed, besides the solar radiation intensities, to the different allochthonous material loads, the tripton sedimentation and the sediment ressuspension caused by the water circulation. The spatial differences in the silicate concentrations and in the water conductivity are due to the geological influences of the watershed of each tributary (Paranapanema, Taquari and das Posses Rivers). The ions and silicate inputs by the three rivers present a different dilution when introduced in each compartment of the reservoir.

a b s t r a c tRotifera density, biomass, and secondary production on two marginal lakes of Paranapanema River were compared after the recovery of hydrologic connectivity with the river (São Paulo State, Brazil). Daily samplings were performed in limnetic zone of both lakes during the rainy season immediately after lateral inflow of water and, in the dry period, six months after hydrologic connectivity recovery. In order to identify the factors that affect rotifer population dynamics, lake water level, volume, depth, temperature, transparency, dissolved oxygen, pH, alkalinity, conductivity, suspended solids, nutrients, and chlorophyll-a were determined. Variations of water physical and chemical factors that affect rotifer population were related to the lake-river degree of connection and to water level rising after drought. The water lateral inflow from the river resulted in an increase in lake water volume, depth, and transparency and a decrease in water pH, alkalinity, and suspended solids. The lake with the wider river connection, more frequent biota exchange, and larger amount of particulate and dissolved materials was richer and more diverse, while rotifer density, biomass, and productivity were lower in both periods studied. Density, biomass, and secondary production were higher in the lake with the smaller river connection and the higher physical and chemical stability. Our results show that the connectivity affects the limnological stability, associated to seasonality. Stable conditions, caused by low connectivity in dry periods, were related with high density, biomass and secondary production. Conversely, instability conditions in rainy periods were associated to elevated richness and diversity values, caused by exchange biota due to higher connectivity.

ABSTRACT. Spatial-temporal variation of Rotifera in an eutrophic reservoir in southern Brazil. We analyzed the spatial and temporal variation of rotifers in a small, shallow and eutrophic reservoir, with intense Cyanobacteria blooms, in seven sampling stations during 17 months (March/2002 to July/2003. Fifty-two taxa were identified, comprising 16 families. Brachionidae, Conochilidae, Synchaetidae, Lecanidae, Collothecidae, Trichocercidae, and Gastropodidae were the most commonly found. Collotheca sp. was abundant in the winter (dry period), while numbers of Conochilus coenobasis and Keratella cochlearis were low. The abundance of Brachionus mirus var. reductus, Filinia longiseta and Keratella lenzi peaked in the summer (rainy season), while for Kellicottia bostonensis, Ploesoma truncatum, Polyarthra remata, Polyarthra vulgaris and Ptygura sp., abundance was highest in the winter, mainly associated with atypical rainfall. Significant differences in the number of taxa and abundance of rotifers were observed during the sampling period. The canonical correspondence analysis explained 46% of the relationship between rotifer abundance and environmental variables, positively correlated with rainfall, nitrite, water temperature, organic nitrogen, nitrate and air temperature. Variations in rotifer abundance were observed a month after changes in the phytoplankton community. Taxa, such as Filinia longiseta, Keratella lenzi and Keratella cochlearis, showed a temporal variation similar to that of other eutrophic reservoirs, while the heterogeneous distribution pattern observed in most taxa could be due to the hydrodynamics of the recently built reservoir and the adverse climatic conditions. KEYWORDS.Water supply, eutrophication, Cyanobacteria. RESUMO.A variação espacial e temporal de rotíferos foi analisada em um reservatório pequeno, raso e eutrófico, com intensas florações de algas Cyanobacteria, em sete pontos de amostragem durante 17 meses (março/2002 a julho/2003). Foram identificados 52 táxons em 16 famílias, sendo Brachionidade, Conochilidae, Synchaetidae, Lecanidae, Collothecidae, Trichocercidae e Gastropodidae as mais frequentes. Collotheca sp. foi abundante no inverno (período seco), enquanto Conochilus coenobasis Skorikov, 1914 e Keratella cochlearis Gosse, 1851 apresentaram baixas abundâncias. Brachionus mirus var. reductus (Koste, 1972), Filinia longiseta (Ehrenberg, 1834) e Keratella lenzi (Hauer, 1953) apresentaram picos de abundância no verão (período chuvoso), e Kellicottia bostonensis (Rousselet, 1908), Ploesoma truncatum (Levander, 1894), Polyarthra remata (Skorikov, 1896), Polyarthra vulgaris Carlin, 1943 e Ptygura sp. no inverno, entretanto, relacionados a chuvas atípicas. Diferenças significativas do número de táxons e da abundância total dos rotíferos ocorreram entre os meses amostrados. A análise de correspondência canônica explicou 46% da relação da abundância dos rotíferos e variáveis ambientais, correlacionados com a pluviosidade, nitrito, temperatura da água, nitrogênio orgânico, nitrato e temp...

A descriptive analysis of the responses of plankton from lakes lateral to a river in its mouth zone into a tropical reservoir to water level variations is presented. Three situations were reported: 1) a comparison of species richness and diversity and of algae population abundance in prolonged drought and in periods of connection of lakes to the river, 2) the spatial distribution of abundance and richness of Rotifera species in four isolated water bodies formed by fragmentation of a lateral lake during a period of prolonged drought and in the same areas during a period of integrity as an ecosystem, 3) the variability of total zooplankton and Cladocera densities at the end of the isolation period of a lateral lake and after the recovery of connection with the river and in a year of continuous connection with the lotic ecosystem. Various idiosyncrasies were observed in connected lateral lakes, like the surface hydrologic connectivity, a primary factor in species richness modifications and a secondary controlling factor of plankton abundance. Underground hydrologic connectivity, through the river → lake water flux during the high-water period and lake → river during drought period, appears to have an important role in richness and abundance variations of planktonic populations in the lake isolated from the river.

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