Mesofauna relacionada a la vegetación acuática en una laguna del valle del alto Paraná argentino

This is a contribution to the knowledge of population structure of that mesofauna related to Paspalum repens and Salvinia herzogii. Samples have been colected in the Laguna Sirena channel monthly, in the period June 1979 - April 1980. It consisted of vegetation and associated fauna sampled with a 250 microns width mesh net. being the sampling area of 1 570 square cm. Peaks of maximun abundance of mesofauna were registered in August 1979 and April 1980, and have been mainly caused by fluctuations in Copepoda, the most numerous group. Similar behaviour was performed by Cladocera. Insecta and Acarina were the same in April. Diptera, chiefly Chironomidae, was a significant fraction of Insecta. Other orders less significant than Diptera, had only a few specimens. Although Planorbidae was the most abundant group of Mollusca. no dense concentrations of this family has been found. This is a contribution to the knowledge of population structure of that mesofauna related to Paspalum repens and Salvinia herzogii. Samples have been colected in the Laguna Sirena channel monthly, in the period June 1979 - April 1980. It consisted of vegetation and associated fauna sampled with a 250 microns width mesh net. being the sampling area of 1 570 square cm. Peaks of maximun abundance of mesofauna were registered in August 1979 and April 1980, and have been mainly caused by fluctuations in Copepoda, the most numerous group. Similar behaviour was performed by Cladocera. Insecta and Acarina were the same in April. Diptera, chiefly Chironomidae, was a significant fraction of Insecta. Other orders less significant than Diptera, had only a few specimens. Although Planorbidae was the most abundant group of Mollusca. no dense concentrations of this family has been found.&nbsp

Invertebrados asociados a los macrófitos sumergidos de los esteros del Iberá (Corrientes, Argentina)

The Iberá system is a waterlogged flatland of 12,000 km2 with several shallow lakes sourrounded by extensive cattail, bulrushed and reedswamps. The area occupied by macrophytes covered about 50% of the total lake area. This contribution reports the quantitative characteristics and the taxonomicstructure of invertebrates associated with five plant species of sumerged macrophytes. Seasonal samples Mere collected with a net of 962 cm2 in area and 125 µm mesh size. The total density of invertebrates showed significant differences in the different species of macrophytes: Cabomba australis, Egeria naias, Ceratophyllum deaersua, Potaangeton sp. y Najas marina. Themost abundant groups were Oligochaeta (particulary in summer time) and Insecta (Quironomidae). The mayority of the invertebrate species occured on most of the plant species, but some were abundant in sedimenta with large deposita of organic matter. As regards the food source and feeding mechanism, the col lectora gatherers or filterers predominated, followed by predatory.The Iberá system is a waterlogged flatland of 12,000 km2 with several shallow lakes sourrounded by extensive cattail, bulrushed and reedswamps. The area occupied by macrophytes covered about 50% of the total lake area. This contribution reports the quantitative characteristics and the taxonomicstructure of invertebrates associated with five plant species of sumerged macrophytes. Seasonal samples Mere collected with a net of 962 cm2 in area and 125 µm mesh size. The total density of invertebrates showed significant differences in the different species of macrophytes: Cabomba australis, Egeria naias, Ceratophyllum deaersua, Potaangeton sp. y Najas marina. Themost abundant groups were Oligochaeta (particulary in summer time) and Insecta (Quironomidae). The mayority of the invertebrate species occured on most of the plant species, but some were abundant in sedimenta with large deposita of organic matter. As regards the food source and feeding mechanism, the col lectora gatherers or filterers predominated, followed by predatory

Distribución de invertebrados asociados a plantas acuáticas en arroyos del Chaco Oriental

This study of invertebrates was restricted to four streams. Their vegetated littoral zone was sampled once a season (in august 1984 and October 1984). Two sampies were collected at six sites with a net of 962 cm2 with a mesh size of 225 microns. Macrophytes and associated invertebrates shortly remain in this water bodies during low water periods.  Different groups of invertebrates on the basis of chosen species according with their highest abundance and special distribution, were determined: I-Stream species group represented by Simulium sp. and Rheotanytarsus sp. II-Species living either in lentic and lotic environments (euryoecious species).III-Species occuring in high salinity waters. Besides, the relative abundance of each group is discussed.This study of invertebrates was restricted to four streams. Their vegetated littoral zone was sampled once a season (in august 1984 and October 1984). Two sampies were collected at six sites with a net of 962 cm2 with a mesh size of 225 microns. Macrophytes and associated invertebrates shortly remain in this water bodies during low water periods.  Different groups of invertebrates on the basis of chosen species according with their highest abundance and special distribution, were determined: I-Stream species group represented by Simulium sp. and Rheotanytarsus sp. II-Species living either in lentic and lotic environments (euryoecious species).III-Species occuring in high salinity waters. Besides, the relative abundance of each group is discussed

Utilización de Lactuca sativa y Panagrellus redivivus para el estudio ecotoxicológico de los ríos Salado y Negro (Chaco, Argentina)

Los ríos Salado y Negro corren por la planicie del Chaco Oriental. El primero atraviesa campos naturales usados para la ganadería donde la ocupación humana es baja. El segundo, un afluente del río Paraná altamente poblado, recibe efluentes urbanos e industriales. La inundación en la región es distintivamente estacional dependiendo de las lluvias de verano. En aguas bajas ambos ríos tienden a ser poco profundos y la concentración salina aumenta. En este estudio usamos bioensayos con Lactuca sativa y Panagrellus redivivus para determinar la toxicidad de los sedimentos y del agua de ambos ríos durante aguas altas y bajas. El bioensayo con lechuga está basado en la habilidad de las semillas para germinar y producir raíces al entrar en contacto con la solución problema. En el ensayo con nemátodos, el crecimiento y desarrollo de los organismos es lento o se detiene bajo condiciones adversas del medio. En Puerto Tiro! (río Negro) hubo decrecimiento de la maduración de los nemátodos y de la elongación de la raíz respecto del control (efectos subletales) usando agua sin tratamiento, extracto de sedimentos y agua concentrada (5 veces). En el río Salado los efectos subletales fueron medidos sólo en la fase de aguas bajas usando agua concentrada y extracto de sedimentos. Se discute la utilidad de ambos bioensayos en ríos que presentan fases de aguas bajas con alta salinidad

Descomposición de macrófltos en bañados de la planicie inundable del río Paraná

This paper deais with foliar decomposition of three macrophytes species from Paraná river non forested wetlands (27°27'S-58°57'W). Loss of both dry weight and nutríent was measured using litter contalners submerged near the sediments. Decomposition rates (k) for Typha latifolia, Thalla multiflora and Paspalum repans were 0,0051; 0,0055 and 0,0092 ct1 respectively. After 170 days, 7 to 8% of the nitrogen initial mass disappearedwhile the percentage loss for the other nutrients were minor than 2%.The abundance of invertebrates per g remaining was approximatety the same from the different plants. Nevertheless, between 30 and 96 days the greatest number of individuáis was recorder in the P. repens litter. In this time, collectors (filterers and gatherars) accounted more than 46% of the macroinvertebrates fbund in the litter containers. This paper deais with foliar decomposition of three macrophytes species from Paraná river non forested wetlands (27°27'S-58°57'W). Loss of both dry weight and nutríent was measured using litter contalners submerged near the sediments. Decomposition rates (k) for Typha latifolia, Thalla multiflora and Paspalum repans were 0,0051; 0,0055 and 0,0092 ct1 respectively. After 170 days, 7 to 8% of the nitrogen initial mass disappearedwhile the percentage loss for the other nutrients were minor than 2%.The abundance of invertebrates per g remaining was approximatety the same from the different plants. Nevertheless, between 30 and 96 days the greatest number of individuáis was recorder in the P. repens litter. In this time, collectors (filterers and gatherars) accounted more than 46% of the macroinvertebrates fbund in the litter containers.&nbsp

The role of vegetated areas on fish assemblage of the Paraná River floodplain: effects of different hydrological conditions

In this paper, we analyze the changes in composition and abundance of fish assemblages in seven vegetated floodplain wetlands with different connectivity across different hydrologic conditions: after a prolonged connection of the floodplain with the main channel, during receding water, and after a prolonged isolation. We also investigated the size and abundance of large-sized migratory species found in these wetlands and the food resources exploited by the dominant fish. Fishes were captured by diurnal seining (8.0 m x 1.50 m, 5 mm mesh) along macrophyte banks. Despite the high total number of species registered (100), sample species richness varied between 7 and 31, depending on the sampling site and the sampling date. Cluster analysis indicated low similarity between sites during both the isolation and the prolonged connection. Species turnover decreased from high water (β = 40.33) to low water (β = 33.83), with the minimum value of beta diversity index obtained during the isolation of the floodplain wetlands (β = 26.83). Our results indicated that different dominant populations of fish occur in different hydrological conditions, even though high water and isolation phases occur in the same season of different years. The ordination (NMDS) indicated the importance of hydrologic conditions in structuring fish assemblages in the studied floodplain. Small-sized characids, typically associated with macrophytes, dominated the fish assemblages, whereas the younger stages of large sized migratory species were found in low abundance. The maximum standard length of the fish captured was 28 cm and for large migratory fish, standard length varied between 1.6 and 25.0 cm. The dominant fish used several food resources, but littoral macrophytes-associated organisms had a high frequency of occurrence in the three hydrologic conditions. The high species richness of fish in the small, vegetated lakes was related to the high spatial heterogeneity during different hydrological conditions. Disturbances in the hydrological pulses could reduce the biodiversity by modifying the connectivity of the floodplain with the river channel. Conservation of these vegetated wetlands requires maintenance of actual width range of connectivity that provide diverse habitat along the time

The role of vegetated areas on fish assemblage of the Paran\ue1 River floodplain: effects of different hydrological conditions

In this paper, we analyze the changes in composition and abundance of fish assemblages in seven vegetated floodplain wetlands with different connectivity across different hydrologic conditions: after a prolonged connection of the floodplain with the main channel, during receding water, and after a prolonged isolation. We also investigated the size and abundance of large-sized migratory species found in these wetlands and the food resources exploited by the dominant fish. Fishes were captured by diurnal seining (8.0 m x 1.50 m, 5 mm mesh) along macrophyte banks. Despite the high total number of species registered (100), sample species richness varied between 7 and 31, depending on the sampling site and the sampling date. Cluster analysis indicated low similarity between sites during both the isolation and the prolonged connection. Species turnover decreased from high water (β = 40.33) to low water (β = 33.83), with the minimum value of beta diversity index obtained during the isolation of the floodplain wetlands (β = 26.83). Our results indicated that different dominant populations of fish occur in different hydrological conditions, even though high water and isolation phases occur in the same season of different years. The ordination (NMDS) indicated the importance of hydrologic conditions in structuring fish assemblages in the studied floodplain. Small-sized characids, typically associated with macrophytes, dominated the fish assemblages, whereas the younger stages of large sized migratory species were found in low abundance. The maximum standard length of the fish captured was 28 cm and for large migratory fish, standard length varied between 1.6 and 25.0 cm. The dominant fish used several food resources, but littoral macrophytes-associated organisms had a high frequency of occurrence in the three hydrologic conditions. The high species richness of fish in the small, vegetated lakes was related to the high spatial heterogeneity during different hydrological conditions. Disturbances in the hydrological pulses could reduce the biodiversity by modifying the connectivity of the floodplain with the river channel. Conservation of these vegetated wetlands requires maintenance of actual width range of connectivity that provide diverse habitat along the time

Trophic ecology of the freshwater prawn, Pseudopalaemon bouvieri (Decapoda: Palaemonidae) in Northeastern Argentina, with remarks on population structure.

Freshwater decapod crustaceans are important components of food webs in these environments, but little is known about the diet of species that live in tropical waters. We studied the feeding ecology of the prawn Pseudopalaemon bouvieri and its population structure in two different areas with six lagoons, with a different composition and abundance of aquatic macrophytes. At each site of macrophytes banks, 18 prawns sample was collected with a hand net (1mm mesh size) from 1m². In the laboratory, prawns cephalothorax length was measured, sex determined, and a total of 208 stomachs were examined for food items. Our results showed that the population abundance varied between 10 ind/m2 and 1 411 ind/m2. The cephalothorax length ranged between 6mm and 21mm, and the male:female ratio varied between 0.3 and 1.0, with a higher proportion of ovigerous females (21%) in area one than area two. P. bouvieri is omnivorous, and its diet was principally based on algae, plant remains, Protozoa, Rotifera, Oligochaeta, Crustacea, Insecta, detritus and other items. The analysis of the stomach content did not reveal any significant difference in the diet between juveniles and adults, and males and females of both areas consumed a similar diet (Kruskal-Wallis test p=0.8273). We concluded that the dietary items consumed by prawns and the niche breadth were similar between the two areas, although the proportion of items consumed varied between lagoons of both areas. The density of P. bouvieri was different between areas, but the size of cephalothorax (CL) was similarLos crustáceos decápodos de agua dulce son un componente importante de la cadena trófica, pero poco se sabe sobre la dieta de las especies que viven en aguas tropicales. Nosotros estudiamos la ecología alimentaria del camarón Pseudopalaemon bouvieri y la estructura de su población en dos áreas diferentes con seis lagunas, con una diferente composición y abundancia de macrófitas acuáticas. En cada sitio poblado con macrófitas, se tomaron 18 muestras con una red manual (1mm de tamaño de malla) de 1m². En laboratorio, se midió la longitud de cefalotórax de los camarones y se determinó el sexo. Asimismo, fueron examinados un total de 208 estómagos para determinar su alimentación. Nuestros resultados mostraron que la abundancia de la población varió entre 10 ind/m2 y 1 411 ind/ m2. La longitud de cefalotórax osciló entre 6 y 21mm, y la razón macho:hembra varió entre 0.3 y 1.0, con una mayor proporción de hembras ovígeras (21%) en el área 1 que en el área 2. P. bouvieri es omnívoro y su alimentación se basa principalmente en algas, restos de plantas, protozoos, rotíferos, Oligochaeta, crustáceos, Insecta, detrito y otros ítems. El análisis del contenido estomacal no reveló ninguna diferencia significativa en la dieta entre juveniles y adultos, y los machos y hembras de ambas áreas consumieron una dieta similar (Kruskal-Wallis, p=0.8273). Nosotros concluimos que los ítems alimentarios consumidos por los camarones y la amplitud de nicho fueron similares entre las dos áreas, aunque la proporción de ítems consumidos varió entre lagunas de ambas áreas. La densidad de P. bouvieri fue diferente entre áreas, pero el tamaño del cefalotórax (CL) fue similar

Trophic ecology of the freshwater prawn, Pseudopalaemon bouvieri (Decapoda: Palaemonidae) in Northeastern Argentina: with remarks on population structure

Freshwater decapod crustaceans are important components of food webs in these environments, but little is known about the diet of species that live in tropical waters. We studied the feeding ecology of the prawn Pseudopalaemon bouvieri and its population structure in two different areas with six lagoons, with a different composition and abundance of aquatic macrophytes. At each site of macrophytes banks, 18 prawns sample was collected with a hand net (1mm mesh size) from 1m². In the laboratory, prawns cephalothorax length was measured, sex determined, and a total of 208 stomachs were examined for food items. Our results showed that the population abundance varied between 10 ind/m² and 1 411 ind/m². The cephalothorax length ranged between 6mm and 21mm, and the male:female ratio varied between 0.3 and 1.0, with a higher proportion of ovigerous females (21%) in area one than area two. P. bouvieri is omnivorous, and its diet was principally based on algae, plant remains, Protozoa, Rotifera, Oligochaeta, Crustacea, Insecta, detritus and other items. The analysis of the stomach content did not reveal any significant difference in the diet between juveniles and adults, and males and females of both areas consumed a similar diet (Kruskal-Wallis test p=0.8273). We concluded that the dietary items consumed by prawns and the niche breadth were similar between the two areas, although the proportion of items consumed varied between lagoons of both areas. The density of P. bouvieri was different between areas, but the size of cephalothorax (CL) was similar