Structure of the testate amoebae community in different habitats in a neotropical floodplain.

This study evaluated the differences in composition, abundance and morphology of testate amoebae among different habitats of the same aquatic environment (plankton, aquatic macrophyte and sediment) in the Upper Paraná River floodplain. Triplicate samplings were undertaken monthly at each habitat from April 2007 to March 2008. The structure of the community of testate amoebae was different among the habitats. The species typical for each habitat, according to Indval, were classified by their shell morphology. Arcella species together with Difflugia gramen and Difflugia pseudogramem were more abundant for plankton. Trinema and Phryganella stood out by their abundance and frequency in aquatic macrophytes. Centropyxis was an indicator of sediment. The results indicated a higher frequency of hemispherical and spherical shells in plankton and spherical and elongated shells in aquatic macrophytes. In the sediment, there was a high frequency of elongated species. Our results support the hypothesis that the community of testate amoebae has different structures among the habitats, refuting the idea that the organization of this community in plankton is guided by random events like the resuspension of organisms from the sediment and their displacement from marginal vegetation.

Effects of recurrent disturbances on the periphyton community downstream of a dammed watercourse.

We evaluate experimentally the effect of a sequential disturbance-desiccation-on the structure and dynamics of a periphytic algal community in a semilotic environment of the Upper Paraná River floodplain. We tested the hypothesis that the presence of recurrent disturbances have a direct negative effect on the attributes of the periphyton community. The sequential effect of desiccation on the periphytic community promoted its significant decrease in density, while the same was not observed in species richness. When desiccation was induced in a mature community, there was no difference in the community compared to control. The sequential disturbances on the community of periphytic algae in a mature stage, was characterised by greater stability. It is believed that the effects of variation in water levels caused by upstream reservoirs can likewise also modify the structure and stability of periphytic algae in the Upper Paraná River floodplain.

Effects of recurrent disturbances on the periphyton community downstream of a dammed watercourse / Efeitos de distúrbios sequenciais na comunidade perifítica à jusante de um curso de água represado

We evaluate experimentally the effect of a sequential disturbancedesiccationon the structure and dynamics of a periphytic algal community in a semilotic environment of the Upper Paraná River floodplain. We tested the hypothesis that the presence of recurrent disturbances have a direct negative effect on the attributes of the periphyton community. The sequential effect of desiccation on the periphytic community promoted its significant decrease in density, while the same was not observed in species richness. When desiccation was induced in a mature community, there was no difference in the community compared to control. The sequential disturbances on the community of periphytic algae in a mature stage, was characterised by greater stability. It is believed that the effects of variation in water levels caused by upstream reservoirs can likewise also modify the structure and stability of periphytic algae in the Upper Paraná River floodplain.(AU)

Avaliou-se experimentalmente o efeito de distúrbios sequenciais dessecamento na estrutura e na dinâmica da comunidade de algas perifíticas em um ambiente semilótico da Planície de Inundação do Alto Rio Paraná. Testou-se a hipótese de que a presença de distúrbios recorrentes tem efeito negativo direto nos atributos da comunidade de algas perifíticas. O efeito sequencial do dessecamento sobre a comunidade perifítica promoveu o decréscimo significativo da sua densidade, enquanto que, em relação à riqueza de espécies, o mesmo não foi observado. Quando o dessecamento foi aplicado em uma comunidade madura, em processo avançado de desenvolvimento, não houve diferença na comunidade em relação ao controle. As perturbações sequenciais sobre a comunidade de algas perifíticas em um estágio maduro foi caracterizada por maior estabilidade. Acredita-se que os efeitos da variação do nível da água, causada por reservatórios a montante, podem, do mesmo modo, também modificar a estrutura e a estabilidade de algas perifíticas na Planície de Inundação do Alto Rio Paraná.(AU)

Zooplankton community resilience and aquatic environmental stability on aquaculture practices: a study using net cages.

Fish farming in net cages causes changes in environmental conditions. We evaluated the resilience of zooplankton concerning this activity in Rosana Reservoir (Paranapanema River, PR-SP). Samples were taken near the net cages installed at distances upstream and downstream, before and after net cage installation. The resilience was estimated by the decrease in the groups' abundance after installing the net cages. The zooplankton community was represented by 106 species. The most abundant species were Synchaeta pectinata, S. oblonga, Conochilus coenobasis, Polyarthra dolichoptera and C. unicornis (Rotifera), Ceriodaphnia cornuta, Moina minuta, Bosmina hagmanni and C. silvestrii (Cladocera) and Notodiaptomus amazonicus (Copepoda). The resilience of microcrustaceans was affected in the growing points as this activity left the production environment for longer, delaying the natural ability of community responses. Microcrustaceans groups, mainly calanoid and cyclopoid copepods, had a different return rate. The net cage installation acted as a stress factor on the zooplankton community. Management strategies that cause fewer risks to the organisms and maximize energy flow may help in maintaining system stability.

Biodiversity of zooplankton communities in the Upper Paraná River floodplain: interannual variation from long-term studies.

We investigated the effect of interannual variation of hydrosedimentological regime and connectivity on the zooplankton biodiversity in the Upper Paraná River floodplain. Zooplankton samplings were undertaken between 2000 and 2007, in different environments of the floodplain, including connected and isolated floodplain lakes, backwaters, rivers and channels. The zooplankton included 541 species. Rotifers showed the highest species richness and abundance. Among the zooplankton species, 71 represent new occurrence records for the floodplain. The species accumulation curve showed a continuous increase in gamma diversity, demonstrating the importance of long-term research for accurate knowledge of biodiversity in heterogeneous and dynamic ecosystems, such as the floodplains. Interannual beta diversity among studied years indicated a lesser alteration in community composition in 2001, when a long limnophase period was observed. In most of the environments, the highest species richness values were related to the greatest flooding amplitudes. Flooding amplitude, which is associated with connectivity, favors faunal exchange amongst the environments and between the pelagic and littoral zones. This explains the occurrence of both planktonic and non-planktonic species within the community. On the other hand, mean zooplankton abundance values were higher when a long isolation period occurred. Differences between the potamophase and limnophase amplitude associated with connectivity among the environments were the most important factors for the structure and dynamics of the zooplankton community in the Upper Paraná River floodplain.

Exotic species of zooplankton in the Upper Paraná River floodplain, Daphnia lumholtzi Sars, 1885 (Crustacea: Branchiopoda).

The integrity of aquatic ecosystems is being challenged worldwide by invading species, which has been one of the frequent causes of biodiversity loss. The invader may cause extinctions of vulnerable native species through predation, grazing, competition and habitat alteration. Daphnia lumholtzi G. O. Sars, 1885, a native cladoceran from Australia, Southwestern Asia and North Africa, has recently been found in the Neotropical region. The D. lumholtzi records from the Upper Paraná River floodplain were restricted to the Pombas floodplain lake (22 degrees 47' 55.92" S and 53 degrees 21' 32.58" W) and Pau Véio Backwater (22 degrees 44' 50.76' S and 53 degrees 15' 11.16' W), in 2003 and 2008, respectively. This species can be distinguished from the other Daphnia species registered in Brazil by the conspicuous pointed fornix, the sizes of the tail spine and helmet, and a carapace ventral margin with strong spines. The high temperatures in the tropical region, as well as the increase in water transparency and the decrease in nutrient concentration observed in the environments of the Upper Paraná River floodplain due to the upstream retention by dams, may favor the development of D. lumholtzi populations. The development of populations of D. lumholtzi in natural environments of the Upper Paraná River floodplain may suggest that this species is establishing in the Neotropical region.

Biodiversity of zooplankton communities in the Upper Paraná River floodplain: interannual variation from long-term studies / Biodiversidade de comunidades de zooplâncton na planície de inundação do Alto Rio Paraná: variações interanuais em estudos de longa duração

We investigated the effect of interannual variation of hydrosedimentological regime and connectivity on the zooplankton biodiversity in the Upper Paraná River floodplain. Zooplankton samplings were undertaken between 2000 and 2007, in different environments of the floodplain, including connected and isolated floodplain lakes, backwaters, rivers and channels. The zooplankton included 541 species. Rotifers showed the highest species richness and abundance. Among the zooplankton species, 71 represent new occurrence records for the floodplain. The species accumulation curve showed a continuous increase in gamma diversity, demonstrating the importance of long-term research for accurate knowledge of biodiversity in heterogeneous and dynamic ecosystems, such as the floodplains. Interannual beta diversity among studied years indicated a lesser alteration in community composition in 2001, when a long limnophase period was observed. In most of the environments, the highest species richness values were related to the greatest flooding amplitudes. Flooding amplitude, which is associated with connectivity, favors faunal exchange amongst the environments and between the pelagic and littoral zones. This explains the occurrence of both planktonic and non-planktonic species within the community. On the other hand, mean zooplankton abundance values were higher when a long isolation period occurred. Differences between the potamophase and limnophase amplitude associated with connectivity among the environments were the most important factors for the structure and dynamics of the zooplankton community in the Upper Paraná River floodplain.

O objetivo deste trabalho foi investigar o efeito da variação plurianual do regime hidrosedimentológico e da conectividade sobre a biodiversidade zooplanctônica da planície de inundação do Alto Rio Paraná. As amostragens do zooplâncton foram realizadas entre os anos de 2000 a 2007, em distintos ambientes dessa planície de inundação, incluindo lagoas abertas, lagoas fechadas, ressacos, rios e canais. A comunidade zooplanctônica foi constituída por 541 espécies, sendo os rotíferos o grupo mais especioso e abundante. Dentre essas espécies, 71 representam novas ocorrências para a planície de inundação. A curva de acumulação de espécies mostrou um incremento continuo da diversidade gama evidenciando a importância de estudos de longa duração para o conhecimento da real biodiversidade em ecossistemas heterogêneos e dinâmicos, como são as planícies de inundação. Os resultados da diversidade beta entre os anos estudados mostraram uma menor alteração da composição da comunidade em 2001, quando foi observado um longo período de limnofase. A maior riqueza média de espécies foi associada à grande amplitude de alagamento na maioria dos ambientes. A duração da inundação, associada à conectividade, favorece o intercâmbio de fauna entre os ambientes, bem como entre as regiões pelágica e litorânea, propiciando a ocorrência de espécies planctônicas e não planctônicas na comunidade. Por outro lado, a abundância da comunidade zooplanctônica foi maior quando ocorreu um extenso período de isolamento. Diferenças entre a amplitude de potamofase e a limnofase associada à conectividade entre os ambientes foram fatores preponderantes para estruturação e dinâmica da comunidade zooplanctônica na planície de Inundação do Alto Rio Paraná.

Exotic species of zooplankton in the Upper Paraná River floodplain, Daphnia lumholtzi Sars, 1885 (Crustacea: Branchiopoda) / Espécie exótica de zooplâncton na planície de inundação do Alto Rio Paraná, Daphnia lumholtzi Sars, 1885 (Crustacea: Branchiopoda)

The integrity of aquatic ecosystems is being challenged worldwide by invading species, which has been one of the frequent causes of biodiversity loss. The invader may cause extinctions of vulnerable native species through predation, grazing, competition and habitat alteration. Daphnia lumholtzi G. O. Sars, 1885, a native cladoceran from Australia, Southwestern Asia and North Africa, has recently been found in the Neotropical region. The D. lumholtzi records from the Upper Paraná River floodplain were restricted to the Pombas floodplain lake (22º 47' 55.92" S and 53º 21' 32.58" W) and Pau Véio Backwater (22º 44' 50.76" S and 53º 15' 11.16" W), in 2003 and 2008, respectively. This species can be distinguished from the other Daphnia species registered in Brazil by the conspicuous pointed fornix, the sizes of the tail spine and helmet, and a carapace ventral margin with strong spines. The high temperatures in the tropical region, as well as the increase in water transparency and the decrease in nutrient concentration observed in the environments of the Upper Paraná River floodplain due to the upstream retention by dams, may favor the development of D. lumholtzi populations. The development of populations of D. lumholtzi in natural environments of the Upper Paraná River floodplain may suggest that this species is establishing in the Neotropical region.

A integridade dos ecossistemas aquáticos está sendo desafiada no mundo inteiro por espécies invasoras, as quais tem sido uma das causas freqüentes de perda de biodiversidade. Um invasor pode causar extinções de espécies nativas vulneráveis através de predação, herbivoría, competição e alteração de habitat. Daphnia lumholtzi G. O. Sars, 1885, cladócero nativo da Austrália, sudeste da Ásia e norte da África, recentemente tem sido registrado na região neotropoical. Os registros de D. lumholtzi na planície de inundação do Alto Rio Paraná foram restritos a lagoa das Pombas (22º 47' 55.92" S e 53º 21' 32.58" O) e Ressaco do Pau Véio (22º 44' 50.76" S e 53º 15' 11.16" O), em 2003 e 2008, respectivamente. Esta espécie pode ser diferenciada das demais espécies de Daphnia encontradas no Brasil pelos conspícuos fórnices pontiagudos, tamanho dos espinhos caudal e elmo, e margem ventral com espinhos fortes. As elevadas temperaturas na região tropical, o aumento da transparência da água e a redução das concentrações de nutrientes nos ambientes da planície de inundação do alto rio Paraná, devido aos represamentos a montante, podem estar favorecendo o desenvolvimento de populações de D. lumholtzi. O desenvolvimento de populações de D. lumholtzi em ambientes naturais da planície de inundação do alto rio Paraná pode representar o estabelecimento desta espécie na região neotropical.