Jurumirim is a large tropical reservoir with remarkable spatial gradients. This structure seems to be determined by a longitudinal gradient in the trophic conditions along the main axis of the reservoir. Nutrient‐rich waters enter from the main tributary river, Paranapanema, and towards the dam there is a lacustrine zone that is deeper and more oligotrophic. Additional variability is derived from two important lateral components: the entrance of the Taquari River, the second largest tributary, bringing waters with higher pH and alkalinity; and the Ribeirão das Posses arm, a sheltered bay where the hydrodynamic conditions promote a high growth of phytoplankton. However, such a spatial pattern is not static. It can become either more defined, during the dry season (late autumn and winter), or less evident, during the expansion of the lotic conditions in the rainy period (late spring and summer). Seasonal processes of stratification/destratification determine the temporal changes in the lacustrine zone but, unlike the upstream regions, the dam zone of the reservoir seems to be little affected by periodic pulses of modifications produced by intensive rains. The presence of extensive wetlands and oxbow lagoons in the mouth zones of the main rivers also constitutes an important source of spatial variability and should be considered in the future.

Brazil has a variety of aquatic ecosystems and rich freshwater biodiversity, but these components have been constantly damaged by the expansion of unsustainable activities. An array of different conservation strategies is needed, especially the creation of protected areas (PAs, hereafter). However, Brazil's PAs are biased towards terrestrial ecosystems and we argue that current PAs have limited efficacy in the protection of freshwater biodiversity. New PAs should better consider aquatic environments, covering entire basins, rivers and other freshwater habitats. We recommend ways to implement these PAs and provide guidance to avoid social impacts. Freshwater systems in Brazil provide essential goods and services but these ecosystems are being rapidly degraded and will be lost if not adequately protected.

The invertebrate colonization during decomposition of Eichhornia azurea was observed in a lateral lake in the mouth zone of Paranapanema River into Jurumirim Reservoir in two periods of the year. The litter bags method was used for measuring the decomposition rate as well as to evaluate the invertebrates colonization. Forty-two litter bags, measuring 15 × 20 cm in size and 2 mm mesh net, were incubated "in situ". Six litter bags (three for colonization and three for decomposition measurements) were removed after the 1 st , 3 rd , 7 th , 14 th , 28 th , 56 th and 72 nd days of incubation. After each day, the material was carefully cleaned for detritus removal and invertebrate sampling. The biological material was fixed with 4% formaline and then sorted and identified. The remaining plant material was dried in an oven (at 60 o C) and weighed. A fast material loss occurred during the first 24 hours and the decomposition rate was higher during the rainy season than in the dry season. A peak on invertebrate density (110 ind.g.DW -1 ) on the remaining detritus of Eichhornia azurea was recorded in the 56 th day of dry season, when the polyphenol concentration of plant detritus was 0.57 UDO.g.DW -1 . In the rainy season, higher density was found in the 28 th day of incubation, when the polyphenol concentration was 4.36 UDO.g.DW -1 . Apparently, the reduction in the polyphenol concentration was followed by an increase in invertebrate densities. The majority of the species observed in the detritus belongs to the collector group that was dominant after the 7 th and 14 th days in the rainy and dry seasons, respectively.Key words: decomposition, colonization, invertebrate, Eichhornia azurea, lake. RESUMO Decomposição de Eichhornia azurea e colonização por invertebradosA colonização por invertebrados durante o processo de decomposição de Eichhornia azurea foi examinada em duas épocas do ano na zona de desembocadura do Rio Paranapanema,

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...

The diversity of fish species in an transition zone between the River Paranapanema and the head mouth of the Jurumirim Reservoir was evaluated. Fish samples were collected from October 1995 to September 1996, by experimental fishing (gill-nets and sieve), in three marginal shallow lagoons and two channel river zones. Gill-net collections resulted in 21 taxons of native fishes. Detritivorous Characiformes such as Steindachnerina insculpta were predominant. Sieve collections resulted in 31 taxa and the Tetragonopterinae subfamily was the/most representative group, which included small species as Cheirodon stenodon. The equitability index characterized the high heterogeneity of fish numeric abundance, reflecting the dominance of a few groups. A significant relationship between biotic and abiotic variables was indicated by the first canonical function. In comparison with other regions of the drainage basin, the ecotone zone studied indicated a higher species richness and, in the case of some species, fishes in all stages of development. This study demonstrated the necessity to preserve the ecological zone for the fishing and fishery management in the reservoir.

ABSTRACTthe annual variability of the photosynthetic production (PP) by phytoplankton in the lacustrine zone of the Jurumirim reservoir (São Paulo, Brazil) was evaluated in a three-year study to identify recurrent patterns and their causes. Variability in PP was measured daily during two periods of the year (the dry and rainy seasons). An analysis of the PP data failed to identify a recurrent pattern, since the PP values showed no correlation with hydrological factors (rainfall, water level and discharge, and washout) nor, apparently, with the water's nutritional conditions. A principal component analysis revealed that the PP and assimilation ratio were higher when the Po 4 3-and n-nh 4 + contents were low and the z eu /z miX ratios were at their highest. Areal primary productivity can be predicted based on the ratio between the maximum volumetric productivity and the coefficient of vertical extinction of light. however, the biomass integrated for z eu was a poor predictor of areal primary productivity. no correlation was found between water temperature and areal and maximum volumetric productivity. thus, the three-year PP study indicated that the variability pattern is typically chaotic. As for the short-term measurements, the PP was found to be higher in the dry season than in the rainy, although both seasons showed an areal PP variability of 35 to 40%. this pattern was attributed to the daily variation in the nutritional conditions and the magnitude of light penetrating through the water, combined with the mixing of phytoplanktonic cells. A comment about the relationship between primary production by phytoplankton and fish yield is also briefly discussed here.Keywords: primary productivity, phytoplankton, variability, reservoir, light, nutrients. RESUMOVariabilidade anual e de curto prazo na produtividade primária pelo fitoplâncton e fatores abióticos correlatos na Represa de Jurumirim (São Paulo, Brasil)A variabilidade anual da produção fotossintética (PP) pelo fitoplâncton na zona da barragem da represa de Jurumirim (São Paulo, Brasil) foi medida após um estudo no período de três anos sucessivos, com o objetivo de identificar padrões recorrentes e suas causas. medidas da variabilidade da PP em escala diária foram obtidas em dois períodos do ano (estações seca e chuvosa). nenhum padrão recorrente foi verificado nos dados de PP, visto não haver relação de sua variabilidade com nenhum fator hidrológico (precipitação, nível e vazão de água e washout) nem, aparentemente, com as condições nutritivas da água. A análise de componentes principais revelou que a PP e a taxa de assimilação foram mais elevadas na época do ano em que o conteúdo de Po 4 3-e n-nh 4 + foi mais baixo e quando as razões z eu /z miX foram mais elevadas. A produtividade primária/área pode ser estimada pela razão entre a produtividade volumétrica máxima e o coeficiente de extinção vertical da luz. entretanto, a biomassa integrada na z eu foi um pobre preditor da produtividade primária/área. nenhuma correlação foi encontrada entre a temperatura d...

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.

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