ABSTRACT In low-order streams, the processing of allochthonous leaf litter is essential in the carbon/energy flow dynamics. Benthic macroinvertebrates, such as chironomids, play critical roles in the breakdown of allochthonous materials, because their larvae take part in intricate trophic networks and have varied trophic ecologies. We evaluated the effects of intra-annual variability on the input of allochthonous leaf litter, and the interactions of leaf-detritus on the succession of Chironomidae assemblages in the dry, rainy, and transition seasons (rainy-dry and dry-rainy). The study took place in a stream in the Brazilian Cerrado. Leaves were incubated in the stream to ascertain the colonization process by Chironomidae and the loss of leaf litter mass after 90 days. Functional feeding groups (FFG) were less rich and less abundant in the dry and dry-rainy seasons, than in the other seasons. The FFG composition of Chironomidae demonstrated that temporal variation between seasons was affected by the exposure time of the leaf-detritus in the stream, and there was more segregation during the dry and rainy seasons. In conclusion, the colonization of leaf-detritus by Chironomidae larvae depended on how long allochthonous plant material remained in the stream, and the variability of the organic matter dynamics input into the stream.

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.

Abstract We evaluated the worldwide trends in studies of the active and dormant forms of microcrustaceans in rice fields, and the potential of this environment as a stock of diversity through a scientometric analysis. Web of Science and Scopus databases were used to compile the 77 studies published before 2019. Publications were distributed over 35 years, with a positive correlation between the number of studies and the year of publication (rho = 0.34). The identified studies were from 18 countries, and 58.4% were conducted in Japan, Italy, the United States, and Spain. Most studies addressed more than two groups of microcrustaceans (37.6%), followed by those focused on Cladocera (27.2%) and Ostracoda (18.1%). We quantified 301 species from six groups of microcrustaceans, the majority of which were Cladocera (41.5%) and Ostracoda (39.8%). The greatest richness of microcrustaceans identified in studies were found in Italy, Thailand, Malaysia, Spain, France, Japan, and Brazil. Of the studies, 87% were centered on the active forms of microcrustaceans rather than dormant forms. We found that 15.5% of the countries that grow rice have identified the richness of microcrustaceans, and even though they are artificial environments, rice fields have high potential to store a high diversity of microcrustaceans.

ABSTRACT Stream insects use in different ways the stream habitats which affect patterns of species occurrence on stream. The nestedness is one of these patterns being an ecological mechanism that generates beta diversity. In this study, we verify the effects of temporal environmental variations on nestedness patterns of Chironomidae assemblages on subtropical streams. We collected chironomid larvae during winter and summer during three years (2010, 2011 and 2012) in Brazilian Subtropical low-order streams (Erechim, state of Rio Grande do Sul, Brazil). We measured environmental variables in each stream. To assess if assemblages will show nested patterns intra- and interannual we used a NODF metric. We observed nestedness only in one year, this pattern was due to variation of limnological factors, which are directly associated with climatic conditions (precipitation and water temperature) and agricultural management (e.g. dissolved oxygen and nutrients). Climatological events affect Chironomidae community through the time. The variations on precipitation values could be one of the mainly factors that influence nestedness for this community. Finally, studies on nesting on time scales should consider inter-annual comparisons, as climatic variations are more evident.

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.

ABSTRACT Changes in the landscape where watersheds are located may affect the stream biota in different ways. In order to explore this idea, we collected freshwater crabs of the genus Aegla Leach, 1820 in subtropical region of southern Brazil. We also measured a number of landscape features and physico-chemical variables in the collection streams and surroundings in order to ascertain which factors affect the occurrence of these crustaceans. A total of 167 individuals of Aegla were collected in 21 streams. The collection was comprised of three species: A. odebrechtii, A. platensis, and A. singularis. The occurrence of A. platensis was influenced by physico-chemical variables (total carbon and total organic carbon) and stream morphometry factors (level curves sum). The occurrence of A. singularis was influenced by land use (pasture and exposed soil and agriculture) and the stream morphometry (level curves sum). Only a small number of A. odebrechtii were collected and their occurrence was influenced by land use (pasture and exposed soil and agriculture). The topography of the area studied limits the types of land use and areas that are less favorable for agriculture (more hilly areas) are have more riparian vegetation (or less anthropic stress). As a result, these areas are less subject to changes in water quality, which is reflected in the distribution of Aegla species.

RESUMEN Los cambios en el paisaje donde se ubican las cuencas hidrográficas pueden afectar la corriente de diferentes maneras. Con el fin de explorar esta idea, se recogieron los cangrejos de agua dulce del género Aegla Leach, 1820 en la región subtropical del sur de Brasil. También se midió una serie de características del paisaje y las variables físico-químicas en los arroyos de colección y el entorno con el fin de determinar qué factores afectan la ocurrencia de estos crustáceos. Un total de 167 individuos de Aegla fueron recolectados en 21 arroyos. La colección estaba compuesta por tres especies: A. odebrechtii, A. platensis y A. singularis. La ocurrencia de A. platensis estuvo influenciada por variables fisicoquímicas (carbono total y carbono orgánico total) y morfometría (suma de curvas de nivel). La ocurrencia de A. singularis estuvo influenciada por el uso de la tierra (pastos y suelo expuesto y agricultura) y la morfometría (suma de curvas de nivel). Sólo un pequeño número de A. odebrechtii fueron recolectados y su ocurrencia fue influenciada por el uso de la tierra (pastos y suelo expuesto y la agricultura). La topografía del área estudiada limita los tipos de uso de la tierra y las áreas menos favorables para la agricultura (zonas más montañosas) tienen más vegetación ribereña (o menos estrés antrópico). Como resultado, estas áreas están menos sujetas a cambios en la calidad del agua, lo que se refleja en la distribución de las especies de Aegla.

ABSTRACT Streams in urban areas are strongly impacted by the input of organic matter and metals, for instance copper (Cu) and zinc (Zn). These metals are essential for the aquatic biota, but when absorbed in excess they are toxic. In Chiro nomidae larvae, the deleterious effects of heavy metals can be ascertained by analyzing the morphological deformities of the larval mentum, a structure of the oral cavity. In this study, we evaluated I) the bioavailability of Cu and Zn in urban stream sediments and II) the relationship between Cu and Zn concentrations and the incidence of deformities in the mentum of Chironomus larvae. Chironomid flies were collected from four locations in two streams at an urban area in southern Brazil. They were identified and the incidence of deformities in the mentum was quantified. Sediment samples were collected at the same locations where larvae were collected, to quantify the bioavailable fractions of Cu and Zn. The concentrations of Cu in the sediment were similar between the collection sites. However, Zn concentrations varied among sites, being greater in the stretch directly influenced by the input of the organic waste. In total, 2,895 Chironomid larvae were collected. The incidence of deformities in the mentum was above 30% and was correlated with the concentrations of Cu (r = 0.68) and Zn (r = 0.87). This correlation indicates that the municipal waste that is thrown into the city’s streams has influenced the occurrence of deformities.

The structure and composition of stream benthic communities are strongly influenced by spatial and temporal factors. This study evaluated the intra and inter-annual variations in Chironomidae communities in subtropical streams. The organisms were sampled from 10 small-order streams during the summer and winter of 2010-2012. The number of chironomid specimens sampled was 7,568, distributed in 49 genera. Chironomid abundance and richness varied intra and inter-annually and community composition varied intra-annually (2010 and 2011). Water temperature, total organic carbon, nitrogen, and rainfall were correlated with chironomid community composition. The intra-annual variation of the community was dependent on climatic variations (temperature and rainfall) and changes caused by intensive agricultural use. We conclude that the temporal variation observed in the Chironomidae community correlates with climatic variations (rainfall) and changes in the total organic carbon and total nitrogen, caused by intensive agricultural land use.

Trabalhos com ecologia de riachos tem buscado compreender os padrões de distribuição das comunidades aquáticas procurando responder de que forma os fatores locais e regionais, infuenciam na ocorrência e persistência de determinadas espécies nesses ecossistemas. Este estudo investigou a infuência dos usos e ocupação da terra sobre a comunidade de Chironomidae em riachos em duas áreas de drenagem no sul do Brasil. Larvas de Chironomidae foram coletadas em riachos de 1a e 2a ordens. A zona ripária dos riachos (30 m em ambas as margens) teve sua paisagem analisada utilizando técnicas de geoprocessamento e diferentes usos e ocupação da terra foram classifcados e quantifcados. Os usos e ocupação da terra foram diferentes entre as duas áreas de drenagem estudadas. Da mesma forma, a composição da comunidade de Chironomidae nos riachos foi diferente entre as duas áreas de drenagem. Dentre os diferentes usos e ocupação da terra quantifcados, a comunidade foi infuenciada principalmente pela agricultura e vegetação arbórea nativa. As variações na paisagem demonstraram que o aumento na área de agricultura e a diminuição da área de vegetação ripária são os principais atributos da paisagem que infuenciam as comunidades de Chironomidae.

Landscape integrity and influence on Chironomidae composition assemblages in small order streams: Studies in stream ecology are aimed at understanding the patterns of distribution of aquatic communities, trying to answer how local and regional factors influence the occurrence and persistence of species in these ecosystems. This study investigated the influence of land use on the Chironomidae community in streams in two drainage areas in southern Brazil. Chironomid larvae were collected in1st and 2nd orders. The riparian zone of streams (30 m on both sides) had its landscape analyzed using GIS techniques, and land uses classified as consistent and non-consistent. The land use influence was different between the two drainage areas. Likewise, the composition of Chironomidae community in streams was different between the two drainage areas. Among the different land uses, the community was influenced mainly by agriculture and arboreous vegetation. We conclude that the aquatic communities respond to environmental changes not only at local scale but also at broader scales, such as landscape features of the surrounding areas.

O material alóctone da mata ripária é fonte importante para a cadeia alimentar detritívora em riachos florestados. Este estudo teve como objetivos i) estimar a perda de massa foliar de Salix humboldtiana Willd., ii) analisar as alterações na composição química dos detritos durante o período de perda de massa, e iii) avaliar a assembleia de invertebrados colonizadoresem um córrego arenoso na planície costeira sul do Rio Grande do Sul (Brasil), com a hipótese de que os detritos de S. humboldtiana constituem habitat favorável a colonização por invertebrados, e que estes contribuem para sua degradação. Foram incubadas 28 bolsas de folhiço na superfície do sedimento do córrego, com retiradas em sete datas amostrais. Mudanças na composição química e a abundância, riqueza e grupos trófi cos funcionais de invertebrados durante a perda de peso foram analisadas. Aos 184 dias foi registrada a perda de 70% da biomassa dos detritos (k=0.0066 dia-1). Foram registrados 14197 organismos, distribuídos em 36 táxons. Oligochaeta (43.6%), Hydrobiidae (16.6%), Chironominae (11.3%) e Hydracarina (6.6%) foram os mais representativos. O desenvolvimento do biofi lme, observado por meio do incremento das concentrações de nitrogênio e fósforo totais nos detritos, pode ter favorecido a colonização por raspadores na fase fi nal do experimento. A hipótese inicial foi corroborada em parte, pois considerando a baixa abundância de potenciais fragmentadores, a contribuição da comunidade de invertebrados para a degradação dos detritos é reduzida, sendo os coletores - catadores o grupo trófi co funcional mais abundante da assembleia.

Aquatic invertebrates associated with Salix humboldtiana litter in a subtropical stream: Allochthonous material from riparian forest is an important source for detritivore food chain in streams. This study aimed to: i) estimate the leaf mass loss of Salix humboldtiana Willd., ii) analyze the changes in the detritus chemical composition during mass loss, and iii) analyze the invertebrate colonizers assemblage of a sandy stream in south coastal plain of the Rio Grande do Sul state (Brazil). We hypothesized that S. humboldtiana debris constitute favorable habitat for colonization by invertebrates, which in turn contribute to debris degradation. Twenty eight bags were incubated on the sediment surface of the stream in seven sampling dates. During the decomposition process we analyzed changes of detritus chemical composition and the abundance, richness and functional trophic groups of invertebrates. After 184 days we recorded an average loss of 70% of debris (k=0.0066 day-1) and counted a total of 14197 invertebrate individuals, distributed in 36 taxa. Oligochaeta (43.6%), Hydrobiidae (16.6%), Chironominae (11.3%) and Hydracarina (6.6%) were the most representative. The biofi lm development, observed through increased concentrations of total phosphorus and nitrogen in the debris, may have favored colonization by scrapers at the end of the decomposition period. The initial hypothesis was partially corroborated as the abundance of potential shredders was low, the contribution of invertebrates assemblage to litter decomposition was low, and the gathering-collectors were the most abundant group.

La partición aditiva de la diversidad de especies es un enfoque prometedor para el análisis de los patrones de diversidad en las comunidades de moluscos, especialmente su distribución espacial. Nuestros objetivos fueron evaluar la distribución de las comunidades de moluscos en los arroyos en el Sur de Brasil, y evaluar la partición de diversidad de la comunidad en diferentes escalas espaciales. El muestreo se llevó a cabo en cuatro cuencas del curso inferior del río Toropi, Brasil. Todas las especies encontradas, y también la comunidad en su conjunto mostraron una distribución agregada. La partición aditiva de la riqueza de especies mostró que la riqueza observada en menor escala (α=dentro de los arroyos) representó el 20.7%, y entre los arroyos (β1) representó el 10.5% de la riqueza total. La riqueza y diversidad de Shannon observadas en escala alfa (α=dentro de los arroyos) fueron mayores que las observadas en el primer nivel de escala de la diversidad beta (β1=entre los arroyos). La mayor variación en las grandes escalas de análisis, con la participación de los componentes entre- órdenes y entre-microcuencas (β2 y β3, respectivamente) fue la esperada, ya que el aumento de la distancia conduce a mayores diferencias de riqueza (mayor diversidad beta). En conclusión, nuestros resultados muestran que la dispersión agregada tuvo influencia en la partición de la diversidad de las comunidades de moluscos en los arroyos estudiados. Los métodos de dispersión y tolerancia a las variaciones de los factores abióticos también juegan un papel importante para determinar la diversidad alfa. Así, la conservación de los arroyos a nivel local contribuirá a la conservación de la cuenca y al mantenimiento de la diversidad regional (gamma).

Additive partitioning of species diversity is a promising approach for analyzing patterns of diversity in mollusk communities, especially their spatial distribution. Our aims were to assess the distribution of mollusk communities in Southern Brazilian streams, and to evaluate the partitioning of community diversity at different spatial scales. The study was carried out in the lower course of the Toropi River, one of the main tributaries of the Ibicuí River Basin, in Southern Brazil. Four microbasins were considered: Sertão da Mata, Ribeirão, Tororaipi and Chiniquá, and sampling were undertaken in autumn, April and May 2009. Six sites were sampled in each stream: two in 1st-order segments, two in 2nd-order segments, and two in 3rd-order segments. All species found and the community as a whole, exhibited a clumped distribution. However, the variance-to-mean ratios for the Drepanotrema kermatoides and Heleobia bertoniana were higher than those of other species, suggesting a higher degree of aggregation. The additive partitioning of the species richness showed that the observed richness at smallest scale (α=within streams) represented 20.7%, and among-streams (β1) represented 10.5% of the total richness. The richness and Shannon diversity index observed at the alpha scale, were higher than those observed at the first level of beta diversity scale (β1=among-streams). The interaction between passive dispersal, tolerance to changes in some environmental variables, abiotic factors, and clumped distribution might have determined the spatial distribution of the communities studied. The greatest variation at the larger scales of analysis, involving among-orders and among-microbasins (β2 and β3, respectively) components, was expected, considering that the increase in distance leads to greater differences in richness (higher beta diversity). In conclusion, our results showed that the clumped distribution influenced the partition of the diversity of the mollusk communities in the streams studied. Dispersal methods and tolerance to variations in abiotic factors also have important roles in determining high alpha diversity. The partitioning of diversity showed that to preserve limnetic mollusks, it is important to preserve local areas, i.e., streams. Accordingly, conservation of streams on a local scale will contribute to conservation of the entire basin and maintenance of regional diversity (gamma).