Abstract Aquatic hyphomycetes are fungi with a fundamental ecological role in forested streams. These organisms are responsible for cycling of nutrients in aquatic environments. However, their structure and composition can be affected when exposed to certain pollutants. Arsenic (As) is a trace element with high toxicity for the aquatic biota. Here we evaluated the effects of different concentrations of Arsenite (AsIII) and Arsenate (AsV) on aquatic hyphomycetes assemblages. To test As toxicity, we conditioned Nectandra megapotamica leaves in a stream and after this period, we incubated leaf discs with stream water and different concentrations of AsIII and AsV. Species richness was negatively affected by both As form. Likewise, the hyphomycetes assemblages presented variation in the composition of species. However, the sporulation rates were not influenced by As. The As showed toxicity on species of hyphomycetes more sensitive, remaining only in species tolerant to its toxicity. In this way, As generated a change in the aquatic hyphomycetes composition. We observed that As had a negative effect on the aquatic hyphomycetes assemblages, regardless of the chemical form. Our results point to the toxicity of this element and its effects on a group that is fundamental to the streams ecosystems functioning.

The aims of this study were to: a) investigate the importance of environmental and/or spatial factors on the composition of the invertebrate community, and b) examine the alpha (α) and beta (β) diversities of the invertebrate community associated to the leaf breakdown process at three different spatial scales (stream reach, stream order and sub-basin). The abiotic variables and colonization of invertebrate community in two detritus (Eucalyptus cloeziana and Inga laurina) were evaluated in 14 sampling sites. For both detritus types, the communities were influenced by environmental matrix. High invertebrate α diversity was related to an increase in water flow velocity (outflow) and orthophosphate levels. High canopy openness and, consequently, high temperatures, showed negative effects on invertebrate α diversity. The α diversity in high-quality litter (E. cloeziana) was mainly influenced by stream order, while β diversity was mainly influenced by sub-basins. However, in low-quality litter (I. laurina), α diversity was mainly influenced by sub-basins, and the β diversity by sampling sites. These findings indicated that changes in detritus quality of the riparian vegetation resulted in significant changes of invertebrate α and β diversity in these communities.

El presente estudio tuvo por objetivos a) investigar la importancia de los factores ambientales o espaciales en la comunidad de invertebrados, y b) examinar las diversidades alfa (α) y beta (β) de la comunidad de invertebrados asociada al proceso de descomposición de hojas, en tres escalas espaciales (segmento de arroyo, orden del arroyo y sub-cuenca). Se evaluaron variables abióticas y la colonización de la comunidad de invertebrados en dos tipos de detritos (Eucalyptus cloeziana y Inga laurina) en 14 sitios de muestreo. En ambos detritos, las comunidades fueron influenciadas por la matriz ambiental. La mayor diversidad α de invertebrados se relacionó con un aumento en la velocidad del flujo de agua (flujo de salida) y con los niveles de ortofosfato. Mayores aperturas de dosel y, en consecuencia, altas temperaturas mostraron efectos negativos sobre la diversidad α de invertebrados. La diversidad α en detritos de mayor calidad química (E. cloeziana) fue influenciada principalmente por el orden del arroyo, mientras que la diversidad beta resultó mayormente influenciada por la sub-cuenca. Sin embargo, en detritos de menor calidad (I. laurina), la diversidad α fue más influenciada por la sub-cuenca, mientras que la diversidad beta, por los sitios de muestreo. Estos hallazgos indicaron que cambios en la calidad de detrito proveniente de la vegetación ribereña resulta en una significativa modificación de la diversidad α y β de invertebrados.

RESUMO Nós investigamos em experimento de campo e de laboratório os efeitos das características foliares e condicionamento microbiano de duas espécies de árvores na abundância, biomassa e preferência alimentar de um fragmentador típico. No experimento de campo, comparamos a associação do Phylloicus (Calamoceratidae, Trichoptera) entre duas espécies vegetais, comumente encontradas em zonas ripárias, que são representativas de alta e baixa qualidade nutricional, respectivamente: Nectandra megapotamica e Chusquea tenella. Em experimento de laboratório, investigamos a preferência alimentar de Phylloicus, usando folhas condicionadas e não condicionadas pelos fungos aquáticos. As mesmas espécies vegetais usadas no experimento de campo foram usadas em laboratório. Inicialmente, as folhas de C. tenella mostraram-se mais nutritivas e macias, enquanto que as de N. megapotamica foram mais duras e lignificadas. Os fragmentadores preferiram o detrito com menor dureza e condicionados pelos fungos (campo: C. tenella; laboratório: N. megapotamica, ambas condicionadas por 14 dias), ou seja, estes parecem ser os fatores determinantes para a escolha dos Phylloicus. Após 14 dias, as folhas de N. megapotamica apresentaram decréscimo na dureza, que está associado ao condicionamento microbiano, e que explicou o padrão de consumo por Phylloicus. Nós encontramos evidências em campo e em laboratório que os Phylloicus são seletivos em relação ao alimento e que as características foliares, especialmente relacionadas à estrutura da folha (ex. dureza foliar e lignina), determinam a associação e a preferência destes fragmentadores.

ABSTRACT Through field and laboratory experiments we investigated the effects of leaf traits of two tree species and microbial conditioning on the abundance, biomass, and feeding preference of a typical macroinvertebrate shredder. In the field, we compared the association of Phylloicus (Calamoceratidae, Trichoptera) with two tree species commonly found in riparian zones, which are representative of high and low nutritional quality, respectively: Nectandra megapotamica and Chusquea tenella. In the laboratory, we investigated the feeding preference of Phylloicus using unconditioned leaves and leaves conditioned by aquatic fungi. The same tree species used in the field experiment were used in the laboratory. Initially, C. tenella leaves were proved to be more nutritious and softer, while N. megapotamica leaves were harder and more lignified. The shredders preferred conditioned leaf detritus of reduced toughness (field: C. tenella; laboratory: N. megapotamica, both conditioned for 14 days). These leaf traits seem to be crucial for the choice process of Phylloicus. After 14 days, N. megapotamica leaves showed a decreased toughness associated with the microbial conditioning, which explained its consumption rate by Phylloicus. In both field and laboratory experiments, we found evidence that Phylloicus is a selective feeding shredder, and that the leaf traits, especially leaf structure (e.g., leaf toughness and lignin content), determine its association and preferences.

In small streams, aquatic community obtains energy mainly from leaves of the riparian vegetation. Processing these leaves involves physical, chemical and biological factors that may difer among leaf species. We assessed the efects of litter quality on leaf decomposition and colonization by aquatic invertebrates in a subtropical stream. Leaves from two native, highly represented tree species common in subtropical riparian areas, Ficus luschnathiana and Gasearía sylvestris, were incubated in coarse mesh bags in a stream. Bags were sampled weekly during an incubation of 28 days. The decomposition rates were higher in leaves of F. luschnathiana than in those of C. sylvestris. In the frst seven days of the experiment, leaves of F. luschnathiana lost ~60% of the initial mass, while Cascarla sylvestris lost around 30%. The leaves of C. sylvestris were initially more palatable than the leaves of F. luschnathiana, perhaps due to their lower lignin and cellulose content, and lignin to N ratio (Lignin:N). These structural compounds enhance leaf toughness thereby protecting them from herbivores and detritivores. However, leaves of F. luschnathiana were comparatively softer, which apparently facilitated fungal colonization and conditioning. Thus, leaves of F. luschnathiana attained high shredders density, which was refected in a higher leaf mass loss. Our results suggest that litter decomposition was sensitive to fungal biomass and leaf toughness. We observed that microbial conditioning, rather than the initial chemical quality of the leaf litter, decreased leaf toughness thereby stimulating further colonization by shredders and enhancing the decomposition process. The fungal community has a key-role in the degradation process within aquatic environments, breaking down even low-quality litter (i.e., F. luschnathiana) and promoting changes in the composition and structure of the invertebrate community.

En arroyos de bajo orden, la comunidad acuática obtiene energía principalmente del aporte de la hojarasca que proviene de la vegetación de la ribera. El procesamiento de las hojas implica medios físicos, químicos y factores biológicos que pueden diferir entre especies vegetales. En esta investigación se evaluó el efecto de la calidad del sustrato sobre el proceso de descomposición y sobre la colonización por invertebrados acuáticos asociados, en un arroyo subtropical. Las hojas de dos especies de árboles nativos, Ficus luschnathiana y Cascarla sylvestris, se incubaron en bolsas de malla gruesa en un arroyo durante 28 días, colectándose muestras semanalmente. Las tasas de descomposición fueron mayores en F. luschnathiana que en C. sylvestris. En los primeros siete días del experimento, F. luschnathiana perdió ~60% de la masa inicial, mientras que C. sylvestris perdió ~30%. Las hojas de C. sylvestris fueron inicialmente más palatables que las de F. luschnathiana, tal vez debido a su menor contenido de lignina y celulosa, y a su más baja relación Lignina:N. Estos compuestos estructurales le conferen rigidez a las hojas, las protegen de los herbívoros y las hacen más resistentes a los detritívoros. Sin embargo, la menor dureza de la hoja de F. luschnathiana facilitó la colonización fúngica, lo cual se refejó, a su vez, en una mayor colonización por invertebrados trituradores y, en general, una mayor pérdida de masa. Los resultados sugieren que la descomposición de la hojarasca fue sensible a la biomasa fúngica y a la dureza de las hojas. Se observó que la colonización microbiana y la disminución de la dureza de las hojas tienen un efecto más fuerte sobre la colonización por invertebrados trituradores y sobre el proceso de descomposición que la calidad química inicial de la hojarasca. La comunidad fúngica es clave en los procesos de degradación en el medio acuático, ya que actúa en la descomposición de la hojarasca, aun en aquella de baja calidad (i.e., F. luschnathiana), promoviendo cambios también en la composición y en la estructura de la comunidad de invertebrados colonizadores.

OBJETIVOS: o objetivo deste estudo foi avaliar a distribuição espacial e temporal dos Chironomidae em riachos subtropicais e investigar a importância dos preditores ambientais na distribuição deste grupo. MÉTODOS: As coletas foram realizadas nas quatro estações anuais entre 2010 e 2011, em dez riachos localizados em matriz agrícola no sul do Brasil, utilizando um amostrador Surber. Os organismos foram identificados até nível de gênero. Algumas variáveis ambientais foram analisadas nos locais de coleta dos Chironomidae. As variações entre abundância e riqueza foram comparadas por meio de uma ANOVA, enquanto que a composição da comunidade foi analisada por meio de uma MANOVA. Uma RDA foi utilizada para avaliar o efeito das variáveis ambientais sobre a comunidade de Chironomidae. RESULTADOS: foram identificados 7,349 indivíduos pertencentes a três subfamílias (Chironominae, Tanypodinae e Orthocladiinae) e 57 gêneros. A abundância e riqueza de Chironomidae foram similares entre os locais e estações do ano. No entanto, a composição variou espacial e temporalmente (p < 0.001). Temperatura da água, carbono orgânico total, nitrogênio total e relação carbono:nitrogênio foram as variáveis que influenciaram a comunidade de Chironomidae. Houve a indicação dos gêneros Thienemanniela, Pentaneura, Paratanytarsus, Parapentaneura, Parametriocnemus, Hudsonimyia, Labrundinea e Larsia para o verão, enquanto que: Parakiefferiella, Paramerina, Metriocnemus foram indicadores para a estação do inverno. CONCLUSÕES: a distribuição espacial dos Chironomidae esteve diretamente relacionada com as condições ambientais dos locais. A variação temporal observada na comunidade seguiu um padrão em relação à temperatura da água. As variáveis físicas e químicas avaliadas podem estar operando como filtros ambientais e com isso alteram a comunidade de Chironomidae.

AIMS: The aims of this study were (i) to evaluate the spatial and temporal distribution of chironomids in subtropical streams and (ii) to investigate the importance of environmental predictors in the distribution of this group. METHODS: Samples were collected in four annual seasons between 2010 and 2011, in 10 streams located in an agricultural matrix in southern Brazil, using a Surber sampler. Organisms were identified to the genus level. Some environmental variables were analysed in the sampling sites of the Chironomidae. The variations in abundance and diversity were compared by Analysis of Variance, whereas the community composition was analysed using Multivariate Analysis of Variance. A Redundance Analysis was used to evaluate the effect of environmental variables on the chironomid community. RESULTS: 7,349 individuals were identified, belonging to three subfamilies (Chironominae, Tanypodinae and Orthocladiinae) and 57 genera. The abundance and richness of the Chironomidae were similar between sites and seasons. However, the composition varied spatially and temporally (p < 0.001). Water temperature, total organic carbon, total nitrogen and carbon:nitrogen ratio were variables that influenced the chironomid community. The genera Thienemanniela, Pentaneura, Paratanytarsus, Parapentaneura, Parametriocnemus, Hudsonimyia, Labrundinea and Larsia were present in summer, whereas Parakiefferiella, Paramerina, Metriocnemus were indicators for winter. CONCLUSIONS: The spatial distribution of chironomids was directly related to the environmental conditions of the sampling sites. The temporal variation in the community followed a pattern in relation to water temperature. The variables physical and chemical operate as environmental filters and thereby alter the chironomid community.

OBJETIVO: O objetivo deste estudo foi testar se o macroconsumidor Aegla longirostri é capaz de modificar a comunidade de invertebrados associados ao folhiço em decomposição. MÉTODOS: O estudo foi realizado em riacho de primeira ordem na região central do Rio Grande do Sul. Foram colocados no riacho dois tipos de canais com pacotes de folhas de Ficus luschnathiana, um canal permitia o acesso dos eglídeos (PA) às folhas e outro restringia o seu acesso (AA), mas ambos permitiam o acesso dos insetos aquáticos. Além disso, foi utilizado um controle (C) onde não havia a presença dos canais. Após 3, 7, 11, 15 e 19 dias foi retirado um pacote de folhas de cada réplica de cada tratamento. RESULTADOS: Foram identificados 926 organismos pertencentes a 19 famílias. O táxon mais comum em todos os tratamentos foi Chironomidae, compreendendo 71% do total e foi representado por 16 gêneros. A presença dos eglídeos diminuiu a abundância total dos organismos em 89% e a riqueza taxonômica em 35%. A presença de A. longirostri modificou a composição taxonômica dos invertebrados e também a estrutura dos grupos tróficos funcionais, promovendo um decréscimo na abundância de todos os grupos, com exceção dos fragmentadores e predadores. O grupo funcional coletor-galhador foi o mais representativo (65%) tanto na presença quanto na ausência de A. longirostri. CONCLUSÃO: Nosso estudo demonstrou que A. longirostri, assim como outros macroconsumidores, é capaz de modificar a estrutura da comunidade de invertebrados que fica aderida às folhas no riacho, corroborando nossa hipótese inicial.

AIM: This study tested whether the macroconsumer Aegla longirostri is able to modify the invertebrate community associated with decomposing leaves. METHODS: The study was performed in a first-order stream located in central Rio Grande do Sul state. Two types of channels containing leaf litter of Ficus luschnathiana were placed in the stream; one type allowed aeglids to access the leaf litter (PA), and the other type did not (AA). Both types allowed aquatic insects to access the leaf litter. In addition, a control treatment (C) was established, in which no channel was used. After 3, 7, 11, 15 and 19 days, a litter bag was removed from each replicate of each treatment. RESULTS: A total of 926 organisms belonging to 19 families were identified. The most common taxon in all treatments was Chironomidae, which comprised 71% of the total and was represented by 16 genera. The presence of aeglids decreased the total abundance of organisms by 89% and the taxonomic richness by 35%. The presence of A. longirostri altered the taxonomic composition of the invertebrates and the structure of the trophic groups, causing a decrease in the abundance of all groups, except for shredders and predators. The gathering-collectors trophic group was the most important (65%), in both the presence and absence of A. longirostri. CONCLUSION: Our study showed that A. longirostri, as well as other macroconsumers, was able to modify the structure of the invertebrate community associated with decomposing leaves in the stream.

OBJETIVOS: O objetivo deste estudo foi avaliar os efeitos da urbanização sobre a ocorrência e distribuição de insetos aquáticos das ordens Ephemeroptera, Plecoptera e Trichoptera (EPT) em seis riachos subtropicais; MÉTODOS: Os organismos foram coletados com um amostrador Surber, durante os anos 2005 e 2006, abrangendo dois ciclos hidrológicos. Foram analisados os valores de abundância, riqueza taxonômica, diversidade Shannon-Wiener e equitabilidade de Pielou. Uma Análise de Componentes Principais (ACP) foi aplicada para avaliar a variabilidade ambiental dos riachos. Uma Análise de Correspondência Canônica (ACC) foi realizada para avaliar os possíveis efeitos das variáveis ambientais sobre os organismos; RESULTADOS: A ACP ordenou os riachos de acordo com sua qualidade, sendo que os riachos Suzana e Nadua apresentaram maiores concentrações de nutrientes. Baetidae (Ephemeroptera) foi a família com maior número de gêneros, 18. Perissophlebiodes Savage, 1983 e Americabaetis Kluge, 1992 foram os gêneros mais frequentes. Anacroneuria Klapálek, 1909 foi o mais abundante dentre os plecópteros coletados e Smicridea Mclachlan, 1871 foi dominante para Trichoptera. A ACC demonstrou que as variáveis pH, condutividade elétrica e velocidade de correnteza foram positivamente correlacionadas ao 1° eixo, enquanto que oxigênio dissolvido foi negativamente correlacionadas o eixo 1; CONCLUSÕES: Os resultados mostram que a distribuição dos insetos aquáticos é afetada por alterações físicas e químicas causadas por atividades urbanas. No entanto, os níveis de perturbação não são suficientemente severos para causar a eliminação de EPT.

AIMS: The objective of this study was to evaluate the effects of urban environments on the distribution and occurrence of aquatic Ephemeroptera, Plecoptera and Trichoptera (EPT) insects in six urban subtropical streams; METHODS: Organisms were collected with a Surber sampler in 2005 and 2006, over two hydrological cycles. We analyzed abundance values, taxonomic richness, Shannon-Wiener diversity and Pielou's evenness. A principal components analysis (PCA) was performed to evaluate the environmental variability of streams. A canonical correspondence analysis (CCA) was performed to evaluate the possible effects of environmental variables; RESULTS: The PCA ordered the streams according to their quality, and Suzana and Nadau streams had higher concentrations of nutrients. The Baetidae (Ephemeroptera) was the family with the highest number of genera (18). Perissophlebiodes Savage, 1983, and Americabaetis Kluge, 1992, were the most common genera. Anacroneuria Klapálek, 1909, was the most abundant Pleocoptera, and Smicridea McLachlan, 1871, was the dominant Trichoptera genus. In the CCA, pH, electrical conductivity and stream velocity were positively correlated with axis 1, whereas dissolved oxygen was negatively correlated with axis 1; CONCLUSIONS: Our results show that the distribution of EPT in urban streams is affected by changes in water physicochemical characteristics. However, these changes are not sufficiently severe to cause the elimination of EPT.

This study evaluates the effects of agricultural and urban activities on the structure and composition of benthic communities of streams in the state of Rio Grande do Sul, Brazil. Benthic macroinvertebrates were collected in streams influenced by urbanization and agriculture and in streams with no anthropogenic disturbances (reference streams). Organism density was superior in urban streams when compared with streams in the other two areas. The taxonomic richness and Shannon diversity index were higher in reference streams. The benthic fauna composition was significantly different among land uses. The classification and ordination analyses corroborated the results of variance analyses demonstrating the formation of clusters corresponding to streams with similar land use. Seasonality was also found to influence the benthic community, though in a lesser degree than land use.