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Riparian areas of riverine plains develop extensive floodable areas named riverine wetlands, which are essential to the water cycle balance and ecosystem dynamics. In this study, we contrasted the hydrological and physicochemical variables of riverine wetlands of both peri-urban areas impacted by intensive farming and those of rural areas with the indicators of the biotic structure (taxonomic richness, Shannon diversity and total density) of benthic diatoms, phytoplankton, zooplankton, macroinvertebrates, chironomids, fishes, turtles, and birds. The study was performed on riverine waters of the Pampean plain, Argentina, with four seasonal samplings conducted in 2017–2018. Our results showed that the significant deepening of the groundwater level caused by aquifer overexploitation in peri-urban areas, as well as the declining surface water quality with higher phosphorus and total nitrogen concentrations, affected the taxonomic richness, diversity, and total density of the biotic assemblages of riverine wetlands. The taxonomic richness of birds, turtles, phytoplankton, chironomids, and fishes was the most sensitive to land use. Phytoplankton, chironomid, and fish diversity showed the greatest differences between rural and peri-urban riverine waters, while the total density of chironomids and birds showed the greatest differences according to land use. The results suggest that the socioeconomic development in those riverine wetlands that still maintain conditions close to the natural ones needs to be subject to guidelines derived from integrated basin management and sustainable urban planning.

El río Chico, ubicado en el centro de Santa Cruz, recorre 600 km desde sus nacientes hasta su desembocadura. En su tramo medio, se encuentra la localidad de Gobernador Gregores (48°45'3"S, 70°14'54"O), que ejerce su influencia sobre el río a través de las actividades agropecuarias y el vertido de efluentes urbanos. Con el objetivo de conocer el grado de impacto sobre la calidad del agua del río, se realizó un análisis de la comunidad de macroinvertebrados bentónicos y se calculó el índice Biotic Monitoring Patagonian Streams (BMPS). En marzo de 2017, se efectuó un primer relevamiento en seis estaciones de muestreo dispuestas en un diseño de gradiente de impacto, con dos estaciones control aguas arriba de la localidad y cuatro estaciones aguas abajo. En cada estación se tomaron muestras de agua para análisis fisicoquímicos, se registraron datos ambientales mediante sonda multiparamétrica y se recolectaron cuatro muestras de macrobentos utilizando una red Surber con malla de 0,5 mm de abertura. Los organismos recolectados fueron identificados y contabilizados bajo microscopios estereoscópico y óptico. Para cada muestra se calculó el número de taxones (S), la abundancia total (N), la diversidad (H’) y la equitatividad (J); los datos de abundancia se analizaron utilizando estadística multivariada. Se identificaron 25 taxones, siendo los mejor representados los oligoquetos Naididae, los hirudíneos, los moluscos Chilinidae y Lymnaeidae, y los insectos Chironomidae, Baetidae y Glossosomatidae. En las estaciones ubicadas aguas abajo más cercanas a la localidad, la comunidad se encontró dominada ampliamente por oligoquetos y quironómidos, y presentó los valores más bajos de S, H’ y J. Los valores de BMPS en esas estaciones indicaron la existencia de aguas contaminadas a fuertemente contaminadas. En las estaciones control y las más alejadas aguas abajo, los valores de S, H’ y J aumentaron significativamente y el índice BMPS indicó mejores condiciones en la calidad ambiental del río. The Chico river, located in the center of Santa Cruz, runs 600 km from its source to its mouth. In its middle reaches, is the town of Gobernador Gregores (48° 45' 3"S, 70° 14' 54" W), which exerts influence on the river through agricultural activities and the discharge of urban sewages. In order to know the degree of impact on the water quality of the river, the analysis of the community of benthic macroinvertebrates was carried out and the Biotic Monitoring Patagonian Streams (BMPS) index was calculated. A first survey was performed in March 2017 at six sampling stations arranged in a gradient design, with two control stations upstream and four stations downstream of the town. At each station, water samples were taken for physicochemical analysis, environmental data were recorded with a multiparameter probe, and four samples of macrobenthos were collected using a Surber network with 0.5 mm mesh. The collected organisms were identified and counted under optic and stereoscopic microscopes. For each sample, species richness (S), total abundance (N), diversity (H’) and evenness (J) were calculated, and the abundance data were analyzed using multivariate statistics. A total of 25 taxa were identified. The best represented were the oligochaetes Naididae, the hirudineans, the mollusks Chilinidae and Lymnaeidae, and the insects Chironomidae, Baetidae and Glossosomatidae. At the stations located downstream closest to the town the community was dominated by oligochaetes and chironomids, and presented the lowest values of S, H’ and J. The values of BMPS at these stations indicated the existence of polluted to heavily polluted water. At the control and the furthest downstream stations, the values of S, H’ and J increased significantly, and the BMPS index indicated better conditions in the environmental quality of the river. Fil: Torres, Santiago Hernan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro de Investigaciones y Transferencia de Santa Cruz. Universidad Tecnológica Nacional. Facultad Regional Santa Cruz. Centro de Investigaciones y Transferencia de Santa Cruz. Universidad Nacional de la Patagonia Austral. Centro de Investigaciones y Transferencia de Santa Cruz; Argentina. Universidad Nacional de la Patagonia Austral. Unidad Académica San Julián; Argentina Fil: Martin, Juan Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro de Investigaciones y Transferencia de Santa Cruz. Universidad Tecnológica Nacional. Facultad Regional Santa Cruz. Centro de Investigaciones y Transferencia de Santa Cruz. Universidad Nacional de la Patagonia Austral. Centro de Investigaciones y Transferencia de Santa Cruz; Argentina. Universidad Nacional de la Patagonia Austral. Unidad Académica San Julián; Argentina Fil: Gárgano, Lucía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro de Investigaciones y Transferencia de Santa Cruz. Universidad Tecnológica Nacional. Facultad Regional Santa Cruz. Centro de Investigaciones y Transferencia de Santa Cruz. Universidad Nacional de la Patagonia Austral. Centro de Investigaciones y Transferencia de Santa Cruz; Argentina Fil: Armendáriz, Laura Cecilia. 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. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo; Argentina

With the purpose of collecting macroinvertebrates for benthic studies of hill streams of the Argentinean Pampean ecoregion, a sampling program was performed in different seasons during 2015. The ingolfiellid crustaceans described in this paper were found only in May 2015 in a sector of the rithron of the Ventana Stream located below the point of the upwelling of hyporheic water, 50 m upstream where the stream is covered by larger conglomerates. The specimens (5 females and 4 males) were measured and photographed, and some were dissected and mounted in Euparal. Appendages of head, pereion and pleon were illustrated. The analysis of the examined material allowed us to conclude that it constitutes a new taxon, Yacana ventania n. gen. n. sp., enlarging the distribution of the family Ingolfiellidae in South America. Characteristics: body long and thin; without eyes; short antennae; inner seta of the outer lobe of maxilla1 is bi-dentate, vestigial molar process and serrations on one side, three spine row elements decreasing in size and the last one toothed; labium present; gnathopod 1 and 2 with a notch on the inner side of the carpus, the carpus of gnathopod 1 has three spines, the proximal one is on the top of a finger-shaped process, while the carpus of gnathopod 2 presents just two spines, propodus in both gnathopods with finger-shaped process at its distal end, a tiny spine and a seta; pereiopods dissimilar, with seta and terminal claw; pereiopod 7 differs from the others in size, number and arrangement of its setae. Uropod 2 longer than uropod 1, uropod 3 small and uniramous; sexual dimorphism clearly present in pleopods and uropod 2 because the females present more rows of setae than males, and probably in the setation of pereiopod 7. Sizes of specimens varied between 3– 8.8 mm. The cladistic analysis (TNT) demonstrates that Yacana ventania n. gen. n. sp. is closely related to South African genera because of the vestigial mandibular palp, also the new taxon here described shared the sexual dimorphism with Stygobarnardia and Trogloleleupia, its discovery gaining relevance on biogeographical aspects and providing new evidence to the theory of continental drift. Type specimens are deposited in the Carcinology Collection of the División Zoología Invertebrados, Museo de La Plata, Argentina., Instituto de Limnología "Dr. Raúl A. Ringuelet"

The city of La Plata, Argentina, is situated in a low alluvial zone, with streams having insufficient drainage into the Río de la Plata estuary. In April 2013, a prodigious storm front caused unprecedented flooding in the city and environs that resulted in extensive loss of life and property, especially in the Del Gato stream basin. Through an analysis of water quality and the conditions of the habitat on the basis of the macroinvertebrates present as bioindicators of environmental quality, this work aims to contribute to a reevaluation of the role of the marshes adjacent to the stream as flood-alleviation elements, and then propose alternatives for flooding management in the basin. Consequently, quantitative seasonal samples of vegetation, sediments, and benthic organic matter were taken and limnologic parameters measured in three sectors of the basin having different land uses: rural, periurban, and urban-industrial. The macroinvertebrate assemblages, as analyzed through the application of ecological indices, exhibited a marked decline in richness and in the Pampean Biotic Index towards the low-lying basin. Principalcomponents analysis associated Site 1 with the dissolved-oxygen concentration, Site 2 with high nitrate values, and Site 3 with oxygen demands. Redundancy analysis indicated a positive relationship between Baetidae and Aeolosomatidae with the dissolved-oxygen concentration and between Enchytraeidae and Stratiomyidae with the conductivity. These marshes are fundamental in maintaining good environmental conditions and attenuating the effects of the flooding that is predicted to become increasingly catastrophic in this region as the climate changes., La ville de La Plata, en Argentine, est située dans une zone alluvionnaire, avec des cours d’eau ayant un écoulement insuffisant dans l’estuaire du Río de la Plata. En avril 2013, un front de tempête exceptionnel a causé des inondations sans précédent dans la ville et dans les environs, qui a entraîné des pertes en vie humaine et en propriétés, en particulier dans le bassin de Del Gato. Grâce à une analyse de la qualité de l’eau et des conditions de l’habitat sur la base des macroinvertébrés présents en tant que bioindicateurs de la qualité de l’environnement, ce travail vise à contribuer à une réévaluation du rôle des marais adjacents à la rivière en tant qu’éléments d’atténuation des inondations et propose ensuite des solutions alternatives pour la gestion des inondations dans le bassin. Simultanément des échantillons saisonniers quantitatifs de végétation, de sédiments et de matières organiques benthiques ont été pris et des paramètres limnologiques mesurés dans trois secteurs du bassin ayant des utilisations de terres différentes : rurales, périurbaines et urbaines-industrielles. Les différences de macroinvertébrés, analysées par l’application d’indices écologiques, ont montré un déclin marqué de la richesse et de l’indice biotique Pampean vers l’aval. L’analyse en composantes principales associe le site 1 avec la concentration en oxygène dissous, le site 2 avec des valeurs élevées de nitrate et le site 3 avec des demandes en oxygène. L’analyse de redondance a indiqué une relation positive des Baetidae et Aeolosomatidae avec la concentration en oxygène dissous et des Enchytraeidae et Stratiomyidae avec la conductivité. Ces marais sont fondamentaux pour maintenir de bonnes conditions environnementales et atténuer les effets des inondations qui devraient devenir de plus en plus catastrophiques dans cette région à mesure que le climat change., Facultad de Ciencias Naturales y Museo

The Puna de Atacama plateau (South America; altitude 3800 m)dwith its endorheic basins and containing one of the principal deposits of lithium worldwidedis one of the most extensive tablelands on the planet. Information on the invertebrates of those internal catchment areas, however, is scarce and fragmentary. We describe here for the first time the structure and composition of the invertebrate assemblage of the Olaroz Salar (Argentina), analyze the spatial-temporal changes, and examine the relationships between the organisms and their environment. Samplings of the sediment and aquatic vegetation were carried out in three affluent streams of the salar during the wet season and the limnologic variables were measured in situ. Of the 26 taxa collected, the most highly represented were Nematoda, Harpacticoida, Paranais litoralis, and Limnocythere sp.; while Heterocypris incongruens registered the highest abundance. The total density was correlated with the sediment organic matter and differed among the streams. The abundance, richness, and diversity decreased upon proximity to the salar. The invertebrate assemblage varied spatially, with the conductivity gradient being one of the principal conditions influencing the distribution. Redundancy-detrended analysis demonstrated that within these environments the conductivity, amount of organic matter, and vegetation were the principal determinants of benthic development. The insularity, fragility, and low resilience of these wetlands necessitate adequate administration policies for their long-term management and utilization, particularly in view of the growing demand for mineral exploitation in the region. Fil: Rodrigues Capitulo, Alberto. 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: Spaccesi, Fernando Gustavo. 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: Armendáriz, Laura Cecilia. 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

One of the possible consequences of climatic change for streams and rivers in the pampean region of South America is an increment in nutrient loads. To analyze this possible perturbation on a biological scale, the response of oligochaetes to an experimental eutrophication of the La Choza Stream, Argentina was studied. We proposed that the addition of nutrients could increase the abundance, biomass, and species composition of the stream. Two stretches (Control and Treatment sites) were selected, with bimonthly samples being taken (March 2007 through February 2009) in two habitat types: the sediments and the aquatic vegetation. On each sampling occasion the environmental variables were measured. The nutrient addition consisted in the continuous dissolution of a commercial fertilizer. The oligochaete mean density and total biomass, the taxonomic richness, the Shannon diversity (H'), and the evenness (E) were calculated and the BACI ANOVA design used to compare the differences between the sites. Thirty-three species of the families Naididae (Naidinae, Pristininae, Tubificinae, and Rhyacodrilinae), Opistocystidae, Enchytraeidae plus Aphanoneura Aeolosomatidae were collected. The oligochaete abundance and biomass increased significantly in the sediments and on the aquatic vegetation, especially among the Naidinae and Pristininae during their asexual reproductive phase. The diversity and evenness varied significantly in the sediments with the nutrient addition. Significant differences in the species richness and diversity were found on the aquatic vegetation, with both increasing at the treatment site after the fertilization. A significant correlation (Spearman) was observed between the oligochaete density in the sediments and the NO 3-N and NH 4-N concentration in the water. The increment in the naidines resistant to the fertilizer throughout the experiment could be explained by the greater nutrient availability, their mode of reproduction, and their short life cycles. The results of our study suggested that the incorporation of nutrients modified the composition of the oligochaete assemblage in favor of herbivores and detrivores. The usefulness of these indicator organisms in monitoring freshwater systems is subsequently discussed., Instituto de Limnología "Dr. Raul A. Ringuelet", Facultad de Ciencias Naturales y Museo

The oligochaete assemblage on the Argentine coast of the Rio de la Plata estuary was sampled seasonally within environments having different types of disturbances. Three habitats were sampled: sediments free of vegetation, sediments within bullrush stands and substrates with Limnoperna fortunei. The species richness, evenness and Shannon–Wiener diversity values were different among those habitats. The only dominant species (according to the Kownacki index) was Nais variabilis. Mean density values varied between 400 and 199,500 ind./m2. Organic matter, ammonium and phosphates correlated positively with the mean oligochaete abundance, but not with the granulometry. Physicochemical variables and nutrient levels were measured and their relation to the sampling sites assessed through a principal component analysis (41.8% cumulative variance). The canonical correspondence analysis (41.2% cumulative variance) indicated that the oligochaetes distributed along both a eutrophication–pollution gradient and a turbidi...

We investigated the responses of the assemblage of Oligochaeta and Aeolosomatidae to organic pollution; comparing taxonomic richness, diversity, abundance, and diet of the individuals inhabiting two lowland streams with different degrees of anthropic impact (the Rodríguez and the Carnaval) belonging to the Río de la Plata basin, Argentina. The physicochemical parameters in the Rodríguez Stream indicated a strong deterioration of the water quality compared to that of the Carnaval. A canonical-correlation analysis indicated that the Tubificinae, Megadrili, Enchytraeidae, and Rhyacodrilinae were more closely associated with the Rodríguez Stream; whereas the Naidinae, Pristininae, and Opystocystidae were more highly represented in the Carnaval. The diversity and taxonomic richness in the Rodríguez Stream exhibited significant differences from those of the Carnaval (P, Facultad de Ciencias Naturales y Museo, Instituto de Limnología "Dr. Raul A. Ringuelet"

Specimens of Uca uruguayensis were collected (n = 1200, 216 megalopae, 984 undifferentiated and adults), counted and classified as males, females or undifferentiated individuals. Each was measured (total carapace width, CW) and weighed (dry weight, DW). The crabs were analyzed and separated into cohorts by the conversion of polymodal width-frequency distributions into normal curves. Six cohorts were recruited during the study period. Two cohorts coexisted in September and December 2001, and April and October 2002, and three in March and June 2001, December 2002, and February 2003. Ovigerous females were captured in December 2001 and 2002, and February 2003; on this last date, megalopal settlement was registered at all the sampling sites. The correlation between CW and DW was analyzed and the growth pattern was modelled by applying the power function (DW = a CWb). Males, females and undifferentiated individuals were examined separately and all together as a group. The data were fitted, indicating a positive allometry for DW, males showing the highest allometric values. To estimate the annual production we used a size-frequency method. Mature individuals, in particular those included in the 10–11.99 mm size class, contributed most to production. On the other hand, few individuals belonged to the size class prior to puberty. Total biomass (expressed in DW) varied between 20 and 611 mg m–2 and the highest values were recorded during summer.

The megalopa stage of the fiddler crab endemic to the Neotropical region, Uca uruguayensis, is redescribed, measured and illustrated from 216 specimens collected at Channel 1, Samborombon Bay, Argentina, the southernmost permanent population of the species. Special attention is given to the description of the types of setae, which are compared to those cited for U. uruguayensis and other fiddler crab megalopae reared in the laboratory. The differences are given in the outline of the carapace, the plumose spines of the telson, and also in the following appendages: antennule, antenna, mandible, maxillule, maxilla, first, second and third maxillipeds. These cited differences could be due to: the origin of the organisms, caught in the field from their settlement area versus reared in the laboratory, and/or the sampling locality. The purpose of the present paper is to provide a detailed description of the megalopa that may allow resolution of taxonomic and phylogenetic relationships within this complex genus.

En esta contribución se cita la fauna de Ostracoda (Crustácea) hallada en los ambientes leníticos interiores de la Isla Martín García, Río de la Plata, Argentina. Se registraron tres especies de Cyprididae; Chlamydotheca incisa (Claus, 1892 ), Strandesia bicuspis bicuspis (Claus, 1892) y S. trispinosa trispinosa (Pinto & Purper, 1965) y una de Cypridopsidae: Cypridopsis vidua (Müller, 1776), siendo el primer registro para la Argentina de S. t. trispinosa y las demás, nuevas citas., In this paper we describe the fauna of Ostracoda (Crustacea) found in lentic water bodies on the island of Martin Garcia in the Rio de la Plata River, Argentina. Three species of Cyprididae are registred: Chlamydotheca incisa (Claus, 1892) Strandesia bicuspis bicuspis (Claus, 1892) and Strandesia trispinosa trispinosa (Pinto & Purper, 1965) and one of Cypridopsidae, Cypridopsis vidua (Müller, 1776). This is the first record of S. t. trispinosa for Argentina and for the other species, new records., Facultad de Ciencias Naturales y Museo

Population dynamics of Stylaria lacustris were analyzed over 2 years in a pond located at Los Talas, Argentina. In both years, the peak in abundance, due to intense asexual reproduction, fell at the end of winter, and was followed by mature individuals. The species was not collected during summer. Temperature was the main factor regulating the population through both sexual and asexual reproduction. In the second year, density was lower and correlated with a lower water level and a reduced vegetation development. Individuals were randomly distributed in periods of high abundance and contagious when density was low. Generation time was 15 days.

An analysis was made of specific richness (S), specific diversity (H), equitability (J), frequency (F), dominance (Dm) and density (D) of the macroinvertebrates associated with the invasive species Limnoperna fortunei (Dunker, 1857), was made. Limnoperna fortunei caused an increase in the specimen number on the rocky environment studied. The species richness and abundance of different taxa of macroinvertebrates, except mollusks was positively related to the presence and density of L.fortunei. Autochthonous gastropod species conversely, tended to be displaced.

The external ultrastructure of Manayunkia speciosa Leidy, 1858 from specimens collected at the lower Uruguay River, South America is described using scanning-electron-microscopy. The branchial crown has a pair of semicircular lateral lobes, a pair of mediodorsal radioles and a pair of medioventral ones. Radiolar surfaces are ciliated. The faecal groove is observed on peristomium middorsally. The anterior margin of the anterior peristomial ring formed a rectangular lobe, with a ciliated band. Chaetal shape exemplifies the basic type of tapering cylinder. Two types of thoracic notochaetae: one wider distally, with a smooth handle, and covered on the surface by denticles, and other are significantly finer at the base and covered by thin structures with a free distal end. These structures were not previously recorded in Fabriciidae. Rows of 3 aligned uncini anteriorly projected are found in the thorax. Each uncinus presents a long manubrium which connects with the crest, extending to a main fang. The teeth of the crest are equal in size. The abdomen present 4 types of neurochaetae: one of small size than the other 3. In the abdomen 10-14 uncini form dense dorsal-transverse-lines. Each uncinus presents a short manubrium. The crest is covered with teeth of similar size., Se describe la ultraestructura externa mediante el uso de SEM de especímenes de Manayunkia speciosa Leidy, 1858, colectados en el Río Uruguay, Sudamérica. La corona branquial presenta un par de lóbulos laterales semicirculares, un par de radiolos en posición mediodorsal y otro medioventral. La superficie de las pínulas es ciliada. Sobre el peristomio se observa un surco fecal mediodorsal. El margen anterior del anillo peristomial anterior está formado por un lóbulo rectangular con una banda ciliada. Las setas son de tipo cilíndrico ahusado. Existen 2 tipos de notosetas torácicas: unas anchas distalmente con mango liso, cubiertas por dentículos sobre su superficie; y otras significativamente más delgadas en la base, cubiertas por extensiones delgadas con extremo distal libre. Estas estructuras son registradas por primera vez en Fabriciidae. El tórax presenta grupos de 3 uncinos alineados, proyectados anteriormente, cada uno presenta un manubrio largo, cresta y diente principal. Los dientes de la cresta son similares en tamaño. En el abdomen se registraron 4 tipos de neurosetas: una pequeña y 3 de mayor tamaño. El abdomen presenta de 10 a 14 uncinos agrupados en una línea transversal dorsal. Cada uncino posee un manubrio corto. La cresta está cubierta por dientes de tamaño similar., Facultad de Ciencias Naturales y Museo, Instituto de Limnología "Dr. Raul A. Ringuelet"

Aim: This study evaluated the use of oligochaetes at different levels of taxonomic resolution as environmental indicators in Argentine lowland streams affected by different land uses. Methods: Sampling sites were grouped based on the physicochemical and habitat characteristics (low-, moderate-, and high-impact disturbance). Collection of the oligochaetes samples was carried out seasonally in sediment and vegetation habitats. Results: The increases in nutrients and organic matter produced elevated densities of the Oligochaeta, but when the disturbance also involved changes in the physical habitat or enhancements in toxic substances, the abundance decreased significantly to values even lower than those of non-impacted environments. The responses of Naidinae and Tubificinae were similar. The density of the Pristininae decreased with increasing impact, but those of the Enchytraeidae and Rhyacodrilinae increased at the most highly impacted sites. The Opistocystidae were not recorded in high-impact sites. Species richness and diversity (H’) were lower in high-impact sites and even lower in sediments. Some species presented no restrictions in the habitat type or with the contamination level: Limnodrilus hoffmeisteri, Dero furcatus, D. digitata, D. pectinata, Pristina longiseta, and P. aequiseta. Moreover, Trieminentia corderoi, Slavina appendiculata, and Aulodrilus pigueti exhibited the highest abundances at low-impact sites and were not registered in high‑impact sites. Conclusions: The Oligochaeta show a relatively wide ecological valence through their extensive number of species. Although lower taxonomic levels can give information about environmental status, test-species’ sensitivities to different types and degrees of contamination will be of utmost relevance to the evaluation of ecological quality., Objetivo: Este estudo analisou as uso de oligoquetos em diferentes níveis de resolução taxonômica como indicadores ambientais em rios de planície Argentina afetadas por diferentes usos da terra. Métodos: Os sítios de amostragem foram agrupados com base nas características físico-químicas e habitat (perturbação baixa, moderada ou alta). Amostras de oligoquetos foram coletadas sazonalmente em habitats de sedimentos e vegetação. Resultados: Os aumentos de nutrientes e matéria orgânica resultaram em densidades elevadas de Oligochaeta, mas quando a perturbação também envolveu mudanças no habitat físico ou incrementos em substâncias tóxicas, a abundância diminuiu de forma significativa para valores ainda mais baixos que os de ambientes naõ perturbados. As respostas dos Naidinae e Tubificinae foram semelhantes. A densidade de Pristininae diminuiu com o aumento da perturbação, mas as densidades de Enchytraeidae e Rhyacodrilinae aumentaram nos locais mais altamente perturbados. Os Opistocystidae não ocorreram em locais de alta perturbação. A riqueza de espécies e a diversidade (H’) foram menores em locais de perturbação elevada e ainda mais baixos nos sedimentos. Algumas espécies não apresentaram restrições no tipo de habitat ou com o nível de contaminação: Limnodrilus hoffmeisteri, Dero furcatus, D. digitata, D. pectinata, Pristina longiseta e P. aequiseta. Além disso, Trieminentia corderoi, Slavina appendiculata e Aulodrilus pigueti exibiram uma maior abundância em locais de baixa perturbação e não foram registrados em locais com elevadas perturbações. Conclusões: Os Oligochaeta apresentaram uma valência ecológica relativamente ampla, através de seu extensivo número de espécies. Embora os níveis taxonômicos mais baixos podem dar informações sobre o status ambiental, testes com espécies com diferentes sesibilidades para diferentes tipos e graus de contaminação serão da maior relevância para a avaliação da qualidade ecológica., Instituto de Limnología "Dr. Raúl A. Ringuelet"

Se estudio el ciclo de vida (marzo de 1996-marzo de 1997) de Dero (Aulophorus) costatus en un cuerpo de agua vegetado de la localidad de Los Talas, Argentina. Fue el naidineo dominante en el ambiente estudiado al modificarse la cobertura vegetal _desarrollandose Azolla sp_ y desplazando la poblacion de Allonais lairdi. Se colectaron individuos inmaduros, maduros y en reproduccion asexual formando cadenas de dos zooides. Se registraron medidas de longitud, peso humedo y peso seco (a 65 °C, 24 h) de los organismos. La disposicion espacial de los individuos, analizada mediante el Indice de Morisita, presento una distribucion al azar. La densidad poblacional presento una gran fluctuacion (1,58 a 101,97 ind./g.d.w.vegetal.m2) debido a la reproduccion de tipo asexual, registrandose dos picos de densidad: en abril, luego de un periodo de intensa reproduccion asexual y en diciembre. La abundancia estuvo correlacionada con la temperatura del agua (coeficiente de Pearson r = 0,5906, p< 0,05) y principalmente con la biomasa vegetal (r = 0,9211, p< 0,001). Los individuos sexualmente maduros fueron hallados en primavera y comienzos del verano (desde octubre hasta enero), comprendiendo una baja proporcion (4,86 %) de la poblacion. En base a la talla y peso de los individuos se estimo la sucesion de tres cohortes: la primera desde octubre a noviembre (incluyendo el periodo de madurez sexual de los organismos), una segunda desde diciembre hasta febrero y la ultima en marzo.

The aim of the present work conducted at the Refugio de Vida Silvestre Bahía Samborombón is to analyse the most relevant aspects of the fecundity of Chasmagnathus granulatus and Uca uruguayensis. Samplings were carried out from March 2001 to February 2003. Ovigerous females of U. uruguayensis (N = 13) and C. granulatus (N = 25) were found during spring and summer, their sizes (CW) varied from 9.1 to 11.7 mm for the former species and from 22.8 to 32.4 mm for the latter. The egg diameter in U. uruguayensis ranged from 245 to 260 ?m for embryos in the early stage of development and from 250 to 345 ?m for those in mid-developmental stage, while in C. granulatus from 250 to 345 μm and from 260 to 365 ?m respectively. Fecundity varied from 1126 to 6745 eggs/brood in U. uruguayensis and 15688-57418 eggs/brood in C. granulatus. For those females with broods in mid-developmental stage, several relationships were made. For U. uruguayensis the best correlation coefficients were obtained for the relationships: female weight vs. egg mass weight and carapace width vs. egg mass weight; for C. granulatus the best association was obtained between female size and the egg number and the egg mass weight., Facultad de Ciencias Naturales y Museo

The experiments carried out with S. lacustris showed that the temperature plays a role of importance in the rate of asexual reproduction, as for the number of zooids produced by individual, as well as to the size reached by them. On the other hand, it would regulate the rate of growth and the sexual reproduction, giving place to the maturity of the individuals when temperature increases. The life time of the immature individuals was estimated in 15 days, being this independent of the temperature used in the cultures. The mature individuals lived on the average 37 days. The survival in S. lacustris was falling gradually, following a curve of type lll. Life expectancy presented its major value at the age of 16 days and stayed approximately constant up to an age of 28 days, after then falled persistently until the last reached age. The individual growth according to von Bertalanffy equation, was estimated for the organisms maintained at 23 ± 2 °C and at 14 ± 1 °C. Those individuals cultivated at higher temperature attained a bigger size, although their rate of growth was smaller than those maintained at 14 °C., Los cultivos realizados con S. lacustris demostraron que la temperatura juega un papel de importancia en la tasa de la reproducción, en cuanto al número de zooides producido por individuo así como también al tamaño alcanzado por los mismos. Por otro lado, regularía la tasa de crecimiento y la reproducción sexual, dando lugar a la madurez de los individuos cuando aumenta la temperatura. El tiempo de vida promedio de los individuos inmaduros se estimó en 15 días, siendo este valor independiente de la temperatura utilizada en los cultivos. Los individuos maduros vivieron en promedio 37 días. La supervivencia en S. lacustris fue decreciendo gradualmente, según una curva de tipo lll. La expectativa de vida presentó su pico a la edad de 16 días y se mantuvo aproximadamente constante hasta una edad de 28 días a partir de la cual fue decreciendo en forma persistente hasta la última edad alcanzada. Se estimó el crecimiento individual, según la ecuación de von Bertalanffy, para los organismos mantenidos a 23 ± 2 °C y a 14 ± 1 °C. En aquellos individuos cultivados a mayor temperatura se registró una mayor talla, aunque su tasa de crecimiento fue menor que la de los individuos mantenidos a 14 °C., Facultad de Ciencias Naturales y Museo

Secondary production of Chasmagnathus granulatus was calculated at the Refugio de Vida Silvestre Bahía Samborombón, Argentina (36° 16′ S and 57° 06′ W). Sampling was conducted on nine occasions between March 2001 and February 2003, crabs were collected by hand, physico-chemical variables, granulometry and organic matter contents of the sediments were registered. Crabs were classified as male, female and undifferentiated, measured (total carapace width: CW) and weighed (wet and dry weight: DW at 60 °C, during 48 hours). A correlation analysis between CW and DW was made. Morphometric growth of C. granulatus was by the application of the power function (y = a x b), where the carapace width (CW) was used as an independent variable. Males, females and undifferentiated individuals were analysed separately as well as all together as a group. The data were fitted indicating a positive allometry (constant of allometry b > 3), the males showing the greatest allometric value. The individuals (n = 957 juveniles and adults) were separated in cohorts by the polymodal width-frequency distribution converted into normal curves. Three cohorts were found during the whole study period, and two cohorts coexisting in each sampling date. Ovigerous females were caught on December 2001, 2002 and February 2003. The size-frequency method was used to estimate the annual production. The major contribution to production was carried out by the mature individuals, in particular those with size between 25 and 30 mm, but on the other hand, only few individuals measuring from 10 to 20 mm were collected. The annual production of C. granulatus was estimated in 7.76 g.m-2. The biomass (expressed as total dry weight) varied between 0.55 and 1.85 g.m-2, with the greater values being registered during autumn and spring, and the lower values during summer., Facultad de Ciencias Naturales y Museo

En este trabajo se da a conocer la fauna de Annelida Oligochaeta, particularmente Naididae de los cuerpos de agua interiores de la Isla Martín García, Río de la Plata Superior, Argentina. Se citan 16 especies de Naididae por primera vez para este sitio, pertenecientes a los géneros Dero (Dero), Dero (Aulophorus), Pristina, Pristinella, Alionáis, Nais, Chaetogaster y Slavina-, una especie de Tubiflcidae Bothrioneurum americanum y dentro de la clase Aphanoneura una especie del género Aeolosoma., In this paper we describe thefauna of Annelida Oligochaeta, particularly Naididaefound in lentic water bodies from Isla Martín Garcia, upper Rio de la Plata estuary, Argentina. Sixteen species ofNaididae are registeredfor the first time in this site belonging to the genera Dero (Dero), Dero (Aulophorus), Pristina. Pristinella. Alionáis, Nais, Chaetogaster and Slavina,- it is also cited one species of Tubiflcidae, Bothrioneurum americanum and a genus belonging to the Class Aphanoneura, Aeolosoma., Facultad de Ciencias Naturales y Museo

The aim of the present work conducted at the Refugio de Vida Silvestre Bahía Samborombón, Argentina, is to analyse the most relevant aspects of the life cycles of Chasmagnathus granulatus and Uca uruguayensis: their abundance, size distribution and sex ratio in order to be used for make management purposes. A total of 1200 individuals of U. uruguayensis (megalopae, juveniles and adults) and 957 individuals of C. granulatus (juveniles and adults) were collected from March 2001 to February 2003. U. uruguayensis had a maximun density of 42 ind./m2 in February 2003, while the maximun density of C. granulatus was 52 ind./ m2 in June 2001. Minimun density was zero individual for both species in July 2002. Each environmental factor sampled (temperature of water, salinity and pH) was correlated with the abundance of each species by Pearson’s linear correlation analysis. Sex ratio did not significantly differ from the expected Mendelian ratio, except for U. uruguayensis in December 2002 (male-biassed) and C. granulatus in June and December 2001, April 2002 and February 2003 (female-biassed). Ovigerous females of U. uruguayensis and C. granulatus were found during the summer., Facultad de Ciencias Naturales y Museo

The objective of this paper is to provide data on the distribution and ecology of oligochaetes and aphanoneurans occurring in the Rio de la Plata, Argentina, including details regarding, their densities, faunal characteristics, species richness, diversity and equitability. Between 1995 and 1997, a total of five stations on the Rio de la Plata were sampled on eight different occasions. The taxocenosis of Oligochaeta and Aphanoneura included 30 species belonging in six families: Naididae, Tubificidae, Narapidae, Enchytraeidae, Lumbricidae and Aeolosomatidae. The density varied between 44495 ind m−2 and 57 ind m−2. Species richness varied between 1 and 17, the diversity ranged from 0.07 to 2.55, and equitability varied between 0.08 and 0.64. According to dominance and frequency, the dominant, constant and widely distributed species were: Nais variabilis, Stephensoniana trivandrana, Amphichaeta leydigi, Chaetogaster diastrophus, Limnodrilus hoffmeisteri, Aulodrilus pigueti, Narapa bonettoi and the species of Enchytraeidae and Aeolosomatidae.