The effect of arsenic on the structure and composition of stream hyphomycetes assemblages.

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.

Microcrustaceans in rice fields: A scientometric analysis from 1977 to 2019.

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.

Latitude dictates plant diversity effects on instream decomposition.

Running waters contribute substantially to global carbon fluxes through decomposition of terrestrial plant litter by aquatic microorganisms and detritivores. Diversity of this litter may influence instream decomposition globally in ways that are not yet understood. We investigated latitudinal differences in decomposition of litter mixtures of low and high functional diversity in 40 streams on 6 continents and spanning 113° of latitude. Despite important variability in our dataset, we found latitudinal differences in the effect of litter functional diversity on decomposition, which we explained as evolutionary adaptations of litter-consuming detritivores to resource availability. Specifically, a balanced diet effect appears to operate at lower latitudes versus a resource concentration effect at higher latitudes. The latitudinal pattern indicates that loss of plant functional diversity will have different consequences on carbon fluxes across the globe, with greater repercussions likely at low latitudes.

Effects of land use and limnology variables on the dissimilarity of common and rare aquatic insects in Atlantic Forest streams / Efectos del uso del suelo y limnología sobre la disimilitud de los insectos acuáticos comunes y escasos en arroyos del bosque atlántico

Abstract Lotic ecosystems are altered at various spatial scales leading to the simplification of water bodies and the dominance or exclusion of certain organisms. In streams, species may have limitations generated by the environment that result in a more abundant or rare occurrence. Thus, the aim of this study was to evaluate the influence of water physical-chemical variables and land use in the drainage basin on the composition of Ephemeroptera, Plecoptera and Trichoptera (EPT) assemblages in the streams of Atlantic Forest. We collected water samples and aquatic insects from 18 streams in Atlantic Forest in southern Brazil. We evaluated the relationship between physical-chemical variables of water and land use and the dissimilarity of EPT assemblages in three different situations: (i) matrix with all organisms collected, (ii) matrix containing only common genera and (iii) matrix containing only the rare genera. We collected 6 023 EPT larvae from 41 genera; 62 % of the individuals belonged to the order Trichoptera, 32 % to the order Ephemeroptera and 6 % to the order Plecoptera. The most common organisms (10 genera) accounted for 86 % of the total abundance of identified individuals. On the other hand, rare genera corresponded to 76 % of the total richness, but only 6 % of the total abundance. For the three matrices studied, the pH, electrical conductivity and riparian vegetation were correlated with the dissimilarity matrix of the three biological datasets used. In our study, we observed that the pH, electric conductivity, exposed soil and riparian vegetation variables were the most important for the dissimilarity of the EPT assemblages. In addition, our results demonstrated that variables at different scales (stream and riparian zone) structure stream insect assemblages. Rev. Biol. Trop. 66(3): 1223-1231. Epub 2018 September 01.

Resumen Los ecosistemas lóticos se alteran a diversas escalas espaciales que conducen a la simplificación de los cuerpos de agua y a la dominancia o exclusión de ciertos organismos. El objetivo de este estudio fue evaluar la influencia de las variables físico-químicas del agua y el uso del suelo en la porción alta de la cuenca del Río Uruguay sobre la composición de los órdenes Ephemeroptera, Plecoptera y Trichoptera (EPT), en los arroyos del bosque atlántico. Se recogieron muestras de agua e insectos acuáticos de 18 arroyos en el bosque atlántico del sur de Brasil. Se evaluó la relación entre las variables físico-químicas del agua y uso del suelo así como la disimilitud de las agrupaciones de EPT en tres situaciones diferentes: (i) matriz con todos los organismos, (ii) matriz que contiene solo géneros comunes y (iii) géneros raros. Se recolectaron 6 023 larvas EPT de 41 géneros; 62 % de los individuos pertenecían al orden Trichoptera, 32 % a Ephemeroptera y 6 % Plecoptera. Los organismos más comunes (10 géneros) representaron el 86 % de la abundancia total de individuos identificados. Por otro lado, la riqueza de géneros raros correspondía al 76 % de la riqueza total, pero sólo al 6 % de la abundancia total. Para las tres matrices estudiadas, el pH, la conductividad eléctrica y la vegetación ribereña se correlacionaron con la matriz de disimilitud de los tres conjuntos de datos biológicos utilizados. En nuestro caso observamos que las variables de pH, conductividad eléctrica, suelo expuesto y vegetación de ribera fueron las más importantes por la disimilitud de los ensamblajes de EPT. Además, nuestros resultados demostraron que las variables a diferente escala (arroyo y zona ribereña) pueden estructurar insectos acuáticos en los arroyos.

Incorporation of zinc and copper by insects of different functional feeding groups in agricultural streams.

Metals from agricultural areas are responsible for soil contamination and are carried into aquatic ecosystems. In this context, we evaluated the incorporation of zinc and copper via three feeding strategies (shredding, herbivory and predators) in assemblages of stream insects. We collected aquatic insects in five agricultural streams and five natural streams in Atlantic forest biome to investigate the accumulation of copper and zinc in insects with different feeding strategies. We found no significant differences in the concentrations of copper and zinc between stream types among all insect-feeding groups compared. However, we observed that copper accumulate concentrations differed significantly among the shredders and predators in relation to their resource in streams, while zinc concentrations differed in the two feeding strategy. Therefore, the investigation of the transfer of copper and zinc by different feeding strategies in streams can contribute to the understanding of changes in aquatic insect assemblages related to agricultural activities around streams.

Plant litter dynamics in the forest-stream interface: precipitation is a major control across tropical biomes.

Riparian plant litter is a major energy source for forested streams across the world and its decomposition has repercussions on nutrient cycling, food webs and ecosystem functioning. However, we know little about plant litter dynamics in tropical streams, even though the tropics occupy 40% of the Earth's land surface. Here we investigated spatial and temporal (along a year cycle) patterns of litter inputs and storage in multiple streams of three tropical biomes in Brazil (Atlantic forest, Amazon forest and Cerrado savanna), predicting major differences among biomes in relation to temperature and precipitation regimes. Precipitation explained most of litter inputs and storage, which were generally higher in more humid biomes (litterfall: 384, 422 and 308 g m-2 y-1, storage: 55, 113 and 38 g m-2, on average in Atlantic forest, Amazon and Cerrado, respectively). Temporal dynamics varied across biomes in relation to precipitation and temperature, with uniform litter inputs but seasonal storage in Atlantic forest streams, seasonal inputs in Amazon and Cerrado streams, and aseasonal storage in Amazon streams. Our findings suggest that litter dynamics vary greatly within the tropics, but point to the major role of precipitation, which contrasts with the main influence of temperature in temperate areas.

Arsenic in stream waters is bioaccumulated but neither biomagnified through food webs nor biodispersed to land.

Human activities such as mining have contributed substantially to the increase of metals in aquatic environments worldwide. These metals are bioaccumulated by aquatic organisms and can be biomagnified along trophic webs. The dispersal of contaminants from water to land has been little investigated, even though most aquatic invertebrates in streams have aerial stages. We used field and laboratory approaches to investigate the effects of arsenic pollution on stream invertebrate assemblages, and its bioaccumulation, biomagnification and trophic transfer from aquatic to terrestrial environments by emergent insects. We conducted the study in an arsenic-impacted stream (40µgL-1 As at the most polluted site) and a reference stream (0.3µgL-1 As). Invertebrate abundance and richness were lowest at the most impacted site. Arsenic in biofilm and in invertebrates increased with the arsenic content in the water. The highest arsenic accumulators were bryophytes (1760µgg-1), followed by the biofilm (449µgg-1) and shredder invertebrates (313µgg-1); predators had the lowest arsenic concentration. Insects emerging from water and spiders along streambanks sampled from the reference and the impacted stream did not differ in their body arsenic concentrations. In the laboratory, the shredder Sericostoma vittatum had reduced feeding rates when exposed to water from the impacted stream in comparison with the reference stream (15.6 vs. 19.0mg leaves mg body mass-1 day-1; p<0.05), but they grew faster in the polluted water (0.16±0.04% day-1vs. 0.05±0.01% day-1, p<0.05). S. vittatum exposed to contaminated stream water accumulated arsenic from food, not through contact with water. We concluded that although arsenic is bioaccumulated, mainly by food ingestion, it is not biomagnified through food webs and is not transported from the aquatic to terrestrial environment when insects leave the stream water.

Distribution and additive partitioning of diversity in freshwater mollusk communities in Southern Brazilian streams.

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 Ibicui 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 (alpha=within streams) represented 20.7%, and among-streams (beta1) 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 (beta1=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 (beta2 and beta3, 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).

Distribution and additive partitioning of diversity in freshwater mollusk communities in Southern Brazilian streams / Distribución y partición aditiva de la diversidad de las comunidades de moluscos de agua dulce en arroyos del Sur de Brasil

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).

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).