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The use of bioindicators requires environmental information and a detailed knowledge of the biota to which it is assign a sensitivity value. The objective of this work was assessing the sensitivity of chironomids to several water quality variables. We used multivariate analysis and occupancy modelling to understand the relationship between abundance and occupancy of chironomid taxa and water quality. The study was performance in 43 sites of eight Pampean streams of Argentina during the fall in 2012 and 2015. We determined the association between 21 taxa of the chironomid assemblage and five variables of water quality (i.e., conductivity, dissolved oxygen, 5-days biochemical oxygen demand, concentrations of phosphate and dissolved inorganic nitrogen). We identified taxa associated to low water quality (e.g., Chironomus calligraphus) and high-water quality (e.g., Rheotanytarsus). In some chironomid taxa their potential as bioindicator increased as the taxonomic level decreased (e.g. Chironominae). However, in other taxa this potential as bioindicator of water quality remains at subfamily level (e.g. Orthocladiinae). The occupancy of Parachironomus sp. and Chironomus calligraphus increased in the sites with the lowest concentration of dissolved oxygen, while Rheotanytarsus sp. and Onconeura analiae behaved in an inverse way. C. calligraphus and O. analiae occupied sites with high values of both, conductivity and 5-days biochemical oxygen demand. C. calligraphus was the single species showing a positive relationship between its occupancy and concentration of phosphate. The occupancy of Allocladius neobilobulatus and Cricotopus sp. were negatively related to the increase of the concentration of nutrients. The description of species sensitivity in terms of occupancy, offers a new methodology to understand how species shows a pattern along abiotic gradient. Further studies about sensitive of local chironomid species to different types of stressors will allow researchers to generate more accurate biotic indices based on these taxa. The water quality of lowland streams would be inferred from the occupancy of chironomid taxa. Fil: Cortelezzi, Agustina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tandil; Argentina. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Exactas. Instituto Multidisciplinario de Ecosistemas y Desarrollo Sustentable; Argentina Fil: Simoy, Maria Veronica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tandil; Argentina. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Exactas. Instituto Multidisciplinario de Ecosistemas y Desarrollo Sustentable; Argentina Fil: Siri, Augusto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Limnología "Dr. Raúl A. Ringuelet". Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Limnología; Argentina Fil: Donato, Mariano Humberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Limnología "Dr. Raúl A. Ringuelet". Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Limnología; Argentina Fil: Cepeda, Rosana Esther. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Exactas. Instituto Multidisciplinario de Ecosistemas y Desarrollo Sustentable; Argentina Fil: Marinelli, Claudia Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tandil; Argentina. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Exactas. Instituto Multidisciplinario de Ecosistemas y Desarrollo Sustentable; Argentina Fil: Berkunsky, Igor. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tandil; Argentina. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Exactas. Instituto Multidisciplinario de Ecosistemas y Desarrollo Sustentable; Argentina

Presentamos el primer registro de Batrachochytrium dendrobatidis infectando poblaciones amenazadas del sapito de panza roja de Tandil (Melanophryniscus aff. montevidensis). Obtuvimos muestras de hisopados de piel de 32 individuos cuyos resultados indicaron una prevalencia del 35.5% y niveles de infección que variaron entre 0.34-915 equivalentes genómicos de Batrachochytrium dendrobatidis. Este hallazgo representa una nueva amenaza que, conjuntamente con la alta fragmentación del hábitat, podría estar afectando la viabilidad de las poblaciones estudiadas. We present the first record of Batrachochytrium dendrobatidis (Bd) infecting endangered populations of the Tandilean Red-belly toad (Melanophryniscus aff. montevidensis). We obtained skin swab samples of 32 individuals. The prevalence was 35.5% and the infection levels varied between 0.34 and 915 Bd-genomic equivalents. This finding represents a new threat that could be affecting, in conjunction with the high habitat fragmentation, the viability of the studied populations. Fil: Agostini, Maria Gabriela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentina Fil: Cortelezzi, Agustina. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Exactas. Instituto Multidisciplinario de Ecosistemas y Desarrollo Sustentable; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Berkunsky, Igor. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Exactas. Instituto Multidisciplinario de Ecosistemas y Desarrollo Sustentable; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Soler, Gabriela. Instituto Superior de Formación Docente y Técnica Nº 10 “Dr. Osvaldo Zarini”; Argentina Fil: Burrowes, Patricia. Universidad de Puerto Rico; Puerto Rico

The objective of the present article is to propose an index that allows the assessment of the fluvial habitat quality in lowland streams that run through urbanized areas, by the use of metrics related to the quality of the watercourse, the river banks, the riparian zone and the fluvial geomorphology. The metrics retained in the index (USHI, Urban Stream Habitat Index) include the cover percentage and quality of the aquatic vegetation; the main features of the river banks; the presence of exotic trees, of litter, of permanent structures (such as buildings) in the riparian zone and other major geomorphological alterations, such as dredging or channelization. The index is related to physical-chemical parameters that are linked to water quality, the imperviousness of the watershed and to other biotic descriptors, particularly the macroinvertebrate and diatom assemblages. The values of the index for the sites in the studied area revealed that 41.2% have a bad or very bad habitat quality, 27.8% a moderate habitat quality, while 31% have a good or very good habitat quality. The main issue detected in the studied sites involved the dredging or partial channelization of the reaches. Unlike other indices that evaluate the quality of the physical habitat through the use of the diatoms or macroinvertebrate communities, the USHI can be interpreted as a measure of the overall quality of the habitat, and uses indicators that do not require the identification of taxa, making it more accessible to non-specialists. Therefore it provides with a tool to evaluate the fluvial habitat quality of lowland streams that can be easily applied, particularly by professionals that take part in the management and decision making process regarding urbanized watersheds., Instituto de Limnología "Dr. Raúl A. Ringuelet"

The selection of breeding sites in response to temporary pond characteristics has been frequently documented in several anuran species. Small and shallow temporary ponds are usually preferred. The Tandilean red-belly toad, Melanophryniscus aff. montevidensis, is an endemic species that breeds in temporary ponds of remnants of highland grasslands in Tandilia mountain system, Buenos Aires Province, Argentina. The goals of this work are to characterize breeding sites of Tandilean red-belly toad, and to assess the availability of potential breeding sites at remnants of highland grasslands. Tandilean red-belly toad was observed using ponds and temporary creeks in valleys and slopes of mountains. The median of dimensions for the breeding sites was 8m length, 4m wide and 10cm depth (n = 40). The majority of the breeding sites were circular and of natural origin. The dominant breeding site substrates were mud and vegetation. We found 115 potential breeding sites in grassland remnants of surroundings of Tandil city, giving a density of 7.1 potential breeding sites/km2. The density of potential breeding sites in highland grasslands of Tandilia Mountains was similar in most surveyed remnants. Therefore, our results suggest that size of remnant is not affecting the breeding habitat availability., Facultad de Ciencias Naturales y Museo

One of the most important effects derived from the intensive land use is the increase of nutrient concentration in the aquatic systems due to superficial drainage. Besides, the increment of precipitations in South America connected to the global climate change could intensify these anthropic impacts due to the changes in the runoff pattern and a greater discharge of water in the streams and rivers. The pampean streams are singular environments with high natural nutrient concentrations which could be increased even more if the predictions of global climate change for the area are met. In this context, the effect of experimental nutrient addition on macroinvertebrates in a lowland stream is studied. Samplings were carried out from March 2007 to February 2009 in two reaches (fertilized and unfertilized), upstream and downstream from the input of nutrients. The addition of nutrients caused an increase in the phosphorus concentration in the fertilized reach which was not observed for nitrogen concentration. From all macroinvertebrates studied only two taxa had significant differences in their abundance after fertilization: Corbicula fluminea and Ostracoda. Our results reveal that the disturbance caused by the increase of nutrients on the benthic community depends on basal nutrients concentration. The weak response of macroinvertebrates to fertilization in the pampean streams could be due to their tolerance to high concentrations of nutrients in relation to their evolutionary history in streams naturally enriched with nutrients. Further research concerning the thresholds of nutrients affecting macroinvertebrates and about the adaptive advantages of taxa in naturally eutrophic environments is still needed. This information will allow for a better understanding of the processes of nutrient cycling and for the construction of restoration measures in natural eutrophic ecosystems., Uno de los efectos más importantes derivados del uso intensivo de la tierra es el aumento de la concentración de nutrientes en los sistemas acuáticos debido al escurrimiento superficial. Además, el incremento de las precipitaciones en América del Sur vinculado al cambio climático global podría intensificar estos impactos antrópicos debido a los cambios en los patrones de escurrimiento y una mayor descarga de agua en los arroyos y ríos. Los arroyos pampeanos son ambientes particulares, con altas concentraciones basales de nutrientes, que podrían incrementarse aún más si las predicciones del cambio climático global se cumplen. En este contexto, se estudió el efecto de la adición experimental de nutrientes en un arroyo pampeano sobre los macroinvertebrados. Los muestreos se llevaron a cabo entre marzo de 2007 y febrero de 2009 en dos tramos seleccionados, aguas arriba y aguas abajo de la entrada de nutrientes. La adición de nutrientes causó un aumento en la concentración de fósforo en el tramo fertilizado, lo que no se observó para la concentración de nitrógeno. De todos los macroinvertebrados estudiados sólo dos taxa tuvieron diferencias significativas en su abundancia después de la fertilización: Corbicula fluminea y ostrácodos. Nuestros resultados revelaron que la perturbación causada por el aumento de nutrientes en una comunidad bentónica depende de la concentración basal de nutrientes. La respuesta débil de macroinvertebrados a la fertilización en las corrientes pampeanas podría ser debido a su tolerancia a altas concentraciones de nutrientes de acuerdo a su historia evolutiva en arroyos enriquecidos naturalmente con nutrientes. Se necesitan nuevas investigaciones sobre los umbrales a partir de los cuales los macroinvertebrados podrían verse afectados y sobre las ventajas adaptativas de los taxones en ambientes eutróficos naturales. Esta información nos permitirá comprender mejor los procesos de reciclaje de nutrientes y así poder pensar medidas de restauración de ecosistemas eutróficos naturales., Facultad de Ciencias Naturales y Museo, Instituto de Limnología "Dr. Raul A. Ringuelet"

We assessed the effects of nutrient enrichment on three stream ecosystems running through distinct biomes (Mediterranean, Pampean and Andean). We increased the concentrations of N and P in the stream water 1.6–4-fold following a before–after control–impact paired series (BACIPS) design in each stream, and evaluated changes in the biomass of bacteria, primary producers, invertebrates and fish in the enriched (E) versus control (C) reaches after nutrient addition through a predictive-BACIPS approach. The treatment produced variable biomass responses (2–77% of explained variance) among biological communities and streams. The greatest biomass response was observed for algae in the Andean stream (77% of the variance), although fish also showed important biomass responses (about 9–48%). The strongest biomass response to enrichment (77% in all biological compartments) was found in the Andean stream. The magnitude and seasonality of biomass responses to enrichment were highly site specific, often depending on the basal nutrient concentration and on windows of ecological opportunity (periods when environmental constraints other than nutrients do not limit biomass growth). The Pampean stream, with high basal nutrient concentrations, showed a weak response to enrichment (except for invertebrates), whereas the greater responses of Andean stream communities were presumably favored by wider windows of ecological opportunity in comparison to those from the Mediterranean stream. Despite variation among sites, enrichment globally stimulated the algal-based food webs (algae and invertebrate grazers) but not the detritus-based food webs (bacteria and invertebrate shredders). This study shows that nutrient enrichment tends to globally enhance the biomass of stream biological assemblages, but that its magnitude and extent within the food web are complex and are strongly determined by environmental factors and ecosystem structure., Instituto de Limnología "Dr. Raúl A. Ringuelet"