Metals contents in two fishes of different feeding behaviour in the Lower Paraná River and Río de la Plata Estuary

Cd, Cr, Cu and Pb concentrations were measured in the water and these plus Zn were measured in the diet, muscle and liver of the detritivorous fish Prochilodus lineatus and the omnivorous fish Pterodoras granulosus at two sites (Lower Paraná River and Río de la Plata right margin) located upstream and downstream, respectively, from Buenos Aires, an important source of xenobiotics. Cu and Cr concentrations in water were higher in the Río de la Plata coastal waters, while Cd and Pb were below detection limits. The stomach contents of P. lineatus showed a higher metal content at the estuary, attaining concentrations within the range reported for contaminated sediments. However, metals in fish tissue were not higher at the estuary and, except for Cd in liver, were lower than in the organic fraction of the stomach content. Thus, only Cd was accumulated. The P. granulosus diet was composed mainly of river vegetation debris and clams, Corbicula fluminea, at the estuary. Cd, Cu and Pb in liver were higher at the estuary while only Cu was higher in the diet at this site. The different nature of the diet seems associated with a differential bioavailability of its metal content. P. granulosus accumulates Cu at both sites and Cd at the estuary. Both fishes showed higher metal content in liver than in muscle. Cr in liver was below detection limits. No relation was found between metal content and fish size. Overall, metal content in fish tissues were low, except for Cu in P. granulosus and Cd in P. lineatus, similar to those of uncontaminated sites, suggesting that homeostatic mechanisms prevent metal accumulation.     

Dynamics of pleustonic ostracod populations in small ponds on the Island of Martín García (Río de la Plata,Argentina)

The biogeography and ecological preferences of Neotropical freshwater ostracods are poorly known, and more so the dynamics of populations and habitat selection of species living in pleustonic environments of temporary ponds. In the present survey we analyze the population changes of ostracods living in pleustonic environments of small freshwater bodies on Martín García Island (Río de la Plata, Argentina). Between June 2005 and June 2007, monthly samples of floating vegetation from eight different ponds on the island were collected, and limnological parameters were measured in situ. The results of multivariate logistic regression showed that the presence of ostracods was significantly related to high dissolved oxygen content and high water temperature. In addition, multivariate regression analysis indicated that, when ostracods were present, their total abundance was negatively related to floating vegetation dry weight. Four ostracod species were found: Strandesia bicuspis, Chlamydotheca incisa, Cypridopsis vidua, and Bradleytriebella trispinosa. The seasonal variation in abundances indicated that populations of the most common species, S. bicuspis and C. incisa, were denser during the summer and autumn months. The results of canonical correspondence analysis showed that individuals of S. bicuspis were more abundant at higher temperatures and lower conductivity than C. incisa. Further research is needed to clarify the observed negative correlation between floating vegetation dry weight and ostracod density and the possible differential thermal preference of the two species studied.     

Aquatic Oligochaeta in some tributaries of the Río de La Plata,Buenos Aires,Argentina

The Oligochaeta of some streams flowing into the Rio de La Plata, Buenos Aires, Argentina, were investigated. Twenty nine taxa (twenty four naidids, five tubificids) were identified. Most species are cosmopolitan, but Dero evelinae, Pristina leidyi, Slavina isochaeta and Bothrioneurum sp. are neotropical. Bratislavia unidentata, Haemonais waldvogeli and Nais pardalis are reported for the first time in Argentina. Variants occurr in the shape of the distal end of the penial sheaths of Limnodrilus hoffmeisteri. The dominant Naidid genera are Dero and Pristina. In the polluted El Gato stream only L. hoffmeisteri and L. claparedeianus were found.     

Dispersion and Ecological Impact of the Invasive Freshwater Bivalve Limnoperna fortunei in the Río de la Plata Watershed and Beyond

Limnoperna fortunei is a freshwater bivalve that invaded South America through Río de la Plata estuary in 1989 and has since become a major macrofouling pest. Along the Paraná-Paraguay waterway, which hosts intense boat traffic, L. fortunei has moved upstream at an average rate of of 250 km per year. In contrast, along the Uruguay river, where boat traffic is restricted to the lowermost 200 km section, upstream colonization is almost 10-times slower. This suggests that attachment to vessels is by far the most important dispersion mechanism. It is suggested that the Amazon, Orinoco and Magdalena basins are under high risk of invasion by this mussel, especially through their estuarine gateways. All South American basins host innumerable water bodies with favorable conditions for L. fortunei’s colonization. Known ecological tolerance limits of the mussel also suggest that it may colonize much of the area from Central America to Canada, including waters that due to their low calcium contents, high temperature and pollution levels, and low oxygen are inadequate for the survival of Dreissena polymorpha. Despite it’s remarkable geographic expansion and its extremely high population densities, L. fortunei’s ecological effects have received very little attention so far. It is suggested that the 2.4-fold increase in Argentine landings of freshwater fish between 1992–1993 and 2000–2001 may be associated with the introduction of this prey species.     

Shell growth of the golden mussel, Limnoperna fortunei (Dunker, 1857) (Mytilidae), in the Río de la Plata, Argentina

The golden mussel, Limnoperna fortunei, is an invasive freshwater bivalve. Since its introduction to Argentina, it had caused damage to the native fauna as well as economic damage to industries of the region. Here, we describe the growth of L. fortunei in a natural temperate environment in Argentina. Age was estimated according to the modal progression method. The constants in the von Bertalanffy growth model were adjusted by an iterative algorithm. Three annual cohorts had similar growth rates. The estimated t ₀ for each cohort showed a temporary displacement in relation to the spawning period.     

A food web analysis of the Río de la Plata estuary and adjacent shelf ecosystem: trophic structure,biomass flows,and the role of fisheries

This article performed a comprehensive assessment of the structure and functioning of the Río de la Plata estuary and adjacent shelf ecosystem, including the effect of fishing. A formerly implemented 37 trophic groups’ mass-balance model (Ecopath) was used to (1) evaluate the particular role of individual biotic components on the ecosystem; (2) characterize the ecosystem in terms of aquatic food web theory; and (3) assess the role of diverse fishing fleets on the ecosystem. Our results indicate a trophic structure and functioning common to other estuaries, where outstanding primary production exceeds consumption, and detritus accumulates in the system. Moreover, our analysis revealed an elevated total system throughput, herbivory outweighing detritivory, and an intermediate state in terms of ecosystem growth and development. Fisheries analyses showed widespread impacts produced by industrial bottom trawl fleets, and specific impacts produced by artisanal fisheries over several groups. Unexpectedly, the evaluation of the effects of fishing showed minor ecosystem consequences by the loss of secondary production and suggests exploitation rates at sustainable levels. This study sets up the basis for temporal ecosystem-level monitoring of the state of the Río de la Plata estuary and adjacent shelf ecosystem.     

Biomass structure and dry matter dynamics of subtropical alluvial and exotic Ligustrum forests at the Río de la Plata,Argentina

Biomass, litterfall, litter standing crop, and decomposition was studied in a native subtropical alluvial forest locally known as Selva Marginal (SM) and an exotic Ligustrum lucidum forest (LF) at the Reserva Integral de Punta Lara, Buenos Aires Province, 34°47S and 58°1W. The alluvial forest site was at the southern limit of distribution of subtropical forests in South America. The Ligustrum forest was invading disturbed areas. Total biomass was 147.7 Mg/ha (86% aboveground and 14% belowground) in the SM, and 71.4 Mg/ha (93% and 7%, respectively) in the LF. Litterfall was 10.3 Mg/ha·yr and 13.8 Mg/ha·yr respectively. Annual leaf decomposition rate was greater for Ligustrum (k=4.07) than for SM species (k=1.48). The mean residence time of aboveground biomass was 12 yr for the SM and 5 yr for the LF. The k₁ values (litterfall/standing crop) were 1.9 and 2.0 for SM and LF respectively. The influence of coastal road and wall in the hydroperiod, native forested wetland ecosystem survival and exotic forest invasion is discussed.     

Phylogeography and Pleistocene demographic history of the endangered marsh deer (Blastocerus dichotomus) from the Río de la Plata Basin

The marsh deer is the largest neotropical cervid with morphological and ecological adaptations to wetlands and riparian habitats. Historically, this now endangered species occupied habitats along the major river basins in South America, ranging from southern Amazonia into northern Argentina to the Paraná river delta. This particularly close association with wetlands makes marsh deer an excellent species for studying the effects of Pleistocene climatic changes on their demographic and phylogeographic patterns. We examined mitochondrial DNA variation in 127 marsh deer from 4 areas distributed throughout the Río de la Plata basin. We found 17 haplotypes in marsh deer from Brazil, Bolivia and Argentina that differed by 1–8 substitutions in a 601 bp fragment of mitochondrial control region sequence, and 486 bp of cytochrome b revealed only 3 variable sites that defined 4 haplotypes. Phylogeny and distribution of control region haplotypes suggest that populations close to the Pantanal area in central Brazil underwent a rapid population expansion and that this occurred approximately 28,000–25,000 years BP. Paleoclimatic data from this period suggests that there was a dramatic increase for precipitation in the medium latitudes in South America and these conditions may have fostered marsh deer’s population growth.     

The distribution and ecology of littoral Oligochaeta and Aphanoneura (Annelida) of the Natural and Historical Reserve of Isla Martín García,Río de la Plata River,Argentina

The objective of this paper is to provide data on the distribution and ecology of oligochaetes and aphanoneurans occurring in the Río 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 Río 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.     

HISH–SIMS analysis of bacterial uptake of algal-derived carbon in the Río de la Plata estuary

One of the main goals of microbial ecologists is to assess the contribution of distinct bacterial groups to biogeochemical processes, e.g. carbon cycling. Until very recently, it was not possible to quantify the uptake of a given compound at single cell level. The advent of nano-scale secondary-ion mass spectrometry (nanoSIMS), and its combination with halogen in situ hybridization (HISH) opened up this possibility. Despite its power, difficulties in cell identification during analysis of environmental samples might render this approach challenging for certain applications. A pilot study, designed to quantify the incorporation of phytoplankton-derived carbon by the main clades of heterotrophic aquatic bacteria (i.e. Alphaproteobacteria, Gammaproteobacteria, Bacteroidetes), is used to exemplify and suggest potential solutions to these technical difficulties. The results obtained indicate that the main aquatic bacterial clades quantitatively differ in the incorporation of algae-derived organic matter. From the methodological point of view, they highlight the importance of the concentration of the target cells, which needs to be sufficient to allow for a rapid mapping under the nanoSIMS. Moreover, when working with highly productive waters, organic and inorganic particles pose a serious problem for cell recognition based on HISH–SIMS. In this work several technical suggestions are presented to minimize the above mentioned difficulties, including alternatives to improve the halogen labeling of the cells and proposing the use of a combination of FISH and HISH along with a mapping system. This approach considerably enhances the reliability of cell identification and the speed of the subsequent nanoSIMS analysis in such complex samples.     

Mechanical aquatic weed management in the lower valley of the Río Negro, Argentina

A major irrigation system in the Lower Valley of the Rió Negro, Argentina, has been invaded by aquatic plants, with Potamogeton illinoensis Morong dominant in irrigation channels and Potamogeton pectinatus L. dominant in drainage channels. Although several other macrophytes are present, problems are largely caused by the dominant species. Results are presented for plant biomass response to weed control treatments using a chain-cutting method in the principal irrigation channel of the system. Peak above-ground biomass of Potamogeton illinoensis was reduced by about 38% by this physical control regime. The treated populations regrew rapidly after spring clearance, but did not regrow after subsequent mid- and late-season clearance operations, even though untreated population biomass remained high during this period. The highest density of Potamogeton illinoensis ramets was found in treated areas. Chain- cutting produced no discernible effect on dissolved oxygen, water temperature, water conductivity, pH or light extinction coefficient compared with untreated check sectors of the channel.     

Field observations of the golden-mantled tamarin, Saguinus tripartitus, on the Río Curaray, Peruvian Amazonia

During a primatological survey on the Río Curaray in north-eastern Peruvian Amazonia, observations on the ecology and behaviour of the golden-mantled tamarin, Saguinus tripartitus, were made. Two groups consisting of 6 and 9 individuals were observed. The diet of one group that was observed in some detail consisted of fruit, insects (tettigoniid orthopterans) and gums. Patterns of height use were very similar to those observed in saddle-back tamarins, Saguinus fuscicollis. This similarity and the lack of evidence for sympatry with either S. fuscicollis or S. nigricollis lead to the suggestion that S. tripartitus should be reconsidered as a subspecies of S. fuscicollis rather than a species on its own; alternatively, other subspecies of S. fuscicollis should be raised in taxonomic rank.     

Yearly reproductive activity of Limnoperna fortunei (Bivalvia) as inferred from the occurrence of its larvae in the plankton of the lower Paraná river and the Río de la Plata estuary (Argentina)

Densities of planktonic larvae of the Asian freshwater invasive pest bivalve Limnoperna fortunei (Dunker) were monitored weekly between 19 September 1997 and 22 January 1999 at two sites: the Paraná de las Palmas river, ca. 130 km north of Buenos Aires (33°57.5 S, 59°12.5 W), and a coastal station on the Río de la Plata estuary, in Buenos Aires (34°33.5 S, 58°24.5 W). Very variable but generally high (up to 25000–35000 ind. m^–3) concentrations were recorded at both sites in September 1997-April 1998, and again in August 1998–January 1999, suggesting continuous reproduction during these months. In May through July 1998 larval densities were generally below 100-200 ind. m^–3. The threshold temperature level associated with the onset and termination of reproduction was ca. 16–17 °C. With the exception of August-September 1998, when Río de la Plata temperatures were below 16.7 °C and larval concentrations less than 1000 ind. m^–3, whereas those of the Paraná were above 16.7 °C, with 1300–13000 larvae m^–3, coupling between the two sites investigated was generally good. Since its invasion in Argentina around 1990, L. fortunei has rapidly become a major nuisance for industrial and power plants located along the lower Paraná and Río de la Plata. The fact that the mollusc produces larvae during 9 months per year greatly hinders its control.     

Detection of Peptidic Sequences in the Ancient Acidic Sediments of Río Tinto,Spain

Biomarkers are molecules that are produced by or can be associated with biological activities. They can be used as tracers that give us an idea of the ancient biological communities that produced them, the paleoenvironmental conditions where they lived, or the mechanism involved in their transformation and preservation. As a consequence, the preservation potential of molecules over time depends largely on their nature, but also on the conditions of the environment, which controls the decomposition kinetics. In this context, proteins and nucleic acids, which are biomolecules bearing biological information, are among the most labile molecules. In this research, we report the presence of short-chained peptides obtained from extracts of ferruginous sedimentary deposits that have been produced under the acidic and oxidizing solutions of Río Tinto, Spain. These preliminary results go against the paradigmatic idea that considers the acidic and oxidizing environments inappropriate for the preservation of molecular information.     

Farming,fishing, and fire in the history of the upper Río Negro region of Venezuela

Studies of Río Negro subsistence farming and fishing activities are used to estimate the human carrying capacity for the region and the likely pattern of human land-use during prehistory. Ceramic evidence suggests human presence in the region more than 3000 years ago. Traditional farming is labor intensive and relatively unproductive. Nevertheless, farmers achieve an energy return of 15.21, and produce 2600 kcal per work hour. Fish are the major protein source, but fish catch per unit of effort and fish yield per hectare of floodplain are very low; fishermen are probably exploiting local fish resources very close to their limit. The low human population density would suggest that the Río Negro forest has been relatively undisturbed. Nevertheless, charcoal is widespread and abundant in forest soils. This charcoal is probably from anthropogenic or natural wildfires. These results suggest a much more complex history for Amazonia than previously thought.K. Clark is a free-lance biologist residing in Lima, Peru     

Impacts of two invasive mollusks, <Emphasis Type="Italic">Rapana venosa</Emphasis> (Gastropoda) and <Emphasis Type="Italic">Corbicula fluminea</Emphasis> (Bivalvia), on the food web structure of the Río de la Plata estuary and nearshore oceanic ecosystem

This paper quantifies the impacts of two invasive species, Rapana venosa (Gastropoda, Muricidae) and Corbicula fluminea (Bivalvia, Corbiculidae), in the food web of the Río de la Plata estuary and adjacent nearshore oceanic ecosystem. We analyzed certain functional traits of these mollusks assessed by a mass balance trophic model previously constructed for the years 2005–2007. This model incorporates 37 functional groups: three marine mammals species, one coastal bird, 17 fishes, 12 invertebrates, two zooplankton, one phytoplankton, and detritus. The model also includes 5 fishing fleets operating in the area. The results showed that the two invasive species affect multiple ecosystem components both directly and indirectly. R. venosa and the whitemouth croaker, Micropogonias furnieri, exhibited a high level of niche overlap (91%), while C. fluminea exhibited a high level of niche overlap with Mytilidae (94%), which suggests in both cases high levels of competition for similar resources. R. venosa had mixed trophic impacts but exhibited a predominantly top down effect on most bivalves. R. venosa could be a threat to natural resources in the area including to the fishing fleets. C. fluminea negatively influenced phytoplankton and detritus biomass and its positive effects on higher trophic level groups suggest a central bottom-up role in the food web as a bentho-pelagic coupler. Both species had negative impacts on the five fleets modeled, showing that the effects of these invasive species could extend to the socio-economic sector.     

Land use effects on erosion and carbon storage of the Río Chimbo watershed, Ecuador

Background and aims

Soil carbon storage is an important component of global carbon cycling. Andean Andisols have high carbon content and are vulnerable to erosion because of agricultural intensification and deforestation. This study examines the effects of land use on erosion and soil carbon storage in the Río Chimbo watershed of Ecuador.

Methods

Soil carbon content, age, and erosion estimated from ¹³⁷Cs inventories was measured along an elevational transect under annual cropping, natural forest, páramo, pasture, and tree plantations.

Results

Land use, particularly annual cropping, affected ¹³⁷Cs levels in the upper soil layers, but did not have an impact on total carbon storage to a depth of 1 m. Relative erosion rates estimated from ¹³⁷Cs inventories at sites under annual cropping averaged 27 t ha^?1?y^?1 over the erosion rate of non-cultivated sites. A linear relationship was observed between soil carbon age (determined by ¹⁴C levels) and ¹³⁷Cs levels, where pasture sites had lower ¹³⁷Cs and older carbon compared to natural forest sites.

Conclusions

The effects of land use on soil loss in the Río Chimbo watershed suggest a loss and/or removal of soil carbon, particularly under annual cropping.     

Microbial community structure across the tree of life in the extreme Río Tinto

Understanding biotic versus abiotic forces that shape community structure is a fundamental aim of microbial ecology. The acidic and heavy metal extreme Río Tinto (RT) in southwestern Spain provides a rare opportunity to conduct an ecosystem-wide biodiversity inventory at the level of all three domains of life, because diversity there is low and almost exclusively microbial. Despite improvements in high-throughput DNA sequencing, environmental biodiversity studies that use molecular metrics and consider entire ecosystems are rare. These studies can be prohibitively expensive if domains are considered separately, and differences in copy number of eukaryotic ribosomal RNA genes can bias estimates of relative abundances of phylotypes recovered. In this study we have overcome these barriers (1) by targeting all three domains in a single polymerase chain reaction amplification and (2) by using a replicated sampling design that allows for incidence-based methods to extract measures of richness and carry out downstream analyses that address community structuring effects. Our work showed that combined bacterial and archaeal richness is an order of magnitude higher than eukaryotic richness. We also found that eukaryotic richness was highest at the most extreme sites, whereas combined bacterial and archaeal richness was highest at less extreme sites. Quantitative community phylogenetics showed abiotic forces to be primarily responsible for shaping the RT community structure. Canonical correspondence analysis revealed co-occurrence of obligate symbionts and their putative hosts that may contribute to biotic forces shaping community structure and may further provide a possible mechanism for persistence of certain low-abundance bacteria encountered in the RT.     

Distribution,status and biology of the tortoise,Geochelone chilensis,in Río Negro Province,Argentina

Morphometric and meristic data from 32 specimens from Río Negro Province do not allow differentiation between G. donosobarrosi and G. chilensis. The significance of morphological and genetic differentiation among Argentinian tortoises is yet to be determined; southern Chaco tortoises undergo ontogenetic and sexual dichromatism. Geochelone chilensis has an extensive latitudinal range (Map 1). Field investigations indicate that Chaco tortoises occupy, and apparently excavate, burrows in the southern portion of the range, prior reports of the species’ southern limit are evaluated and the link between tortoise distribution and “monte”; vegetation is discussed. The season of reproduction and clutch size are noted. Extensive internal pet traffic has markedly affected tortoise populations in some areas; near the southern limit of the range, however, there is little commercial collecting.     

A new species of Paracreptotrema (Digenea,Plagiorchiformes, Allocreadiidae) infecting two species of poeciliids in Río Malila of the Río Pánuco basin,Hidalgo, México,with a key to the species of the genus

Paracreptotrema rosenthali sp. n. was discovered in the intestine of Xiphophorus malinche and Pseudoxiphophorus jonesii, collected from the headwaters of Río Malila, tributary of Río Conzintla, in the Río Pánuco basin, Hidalgo, México, during 2008–2009. The new species differs from the five known species of Paracreptotrema Choudhury, Pérez-Ponce de León, Brooks & Daverdin, 2006 by having vitelline follicles that extend from a level anterior to the pharynx to mid-testes, the seminal vesicle which is more extensively folded, and a wider cirrus sac. The new species resembles Paracreptotrema heterandriae in the length of its ceca, which surpasses the posterior margin of the ovary but do not reach the testes. A key to the species of Paracreptotrema is provided.