Susana José de Paggi

Zooplankton in the Paraná River Floodplain (South America) Before and After the Invasion of Limnoperna fortunei (Bivalvia)

The Asian freshwater invasive bivalve, Limnoperna fortunei (Dunker 1857), was introduced into South America through the Rio de la Plata estuary (Argentina) at the beginning of the 1990s. Between 1995 and 1996, the bivalve was first observed in the middle reaches of Paraná River, 600 km upstream from its original point of entry to the system. Here, we describe the present zooplankton communities of two secondary channels of the Middle Paraná River floodplain (Colastiné and Santa Fe rivers) and contrast them with pre-invasion communities using zooplankton data obtained during 1974–1975 (Sante Fe River) and 1971–1973/1981–1982 (Colastiné River). In both floodplain rivers, total zooplankton and rotifer abundance during low water were significantly lower in the post-invasion period than they were pre-invasion. Prior to invasion, mean zooplankton abundance in low water was greater than in high water, while post-invasion mean zooplankton abundances during low and high water were similar. The rotifer Keratella was significantly more abundant prior to mollusc invasion. Zooplankton abundance and chlorophyll-a concentration declined compared to the pre-invasion period and were not correlated with post-invasion physical factors. Nutrient concentrations increased post-invasion from increased human development, but did not stimulated zooplankton or phytoplankton.

Vertical distribution and diel migration of rotifers in a Parana River floodplain lake

The vertical distribution of zooplankton rotifers in the open waters of Laguna El Tigre was investigated. Rotifers showed a relatively uniform distribution throughout the water column. This pattern of distribution was maintained during the year and did not show variations in relation to hydrologic phases of inundation and isolation of the lake. Diel vertical migration of rotifers from the limnetic and the littoral area was investigated too. In littoral area rotifers exhibited a reverse migration, whereas in the limnetic the movements were less conspicuous. Horizontal migration was observed too, and there were interactions between horizontal and vertical distribution. Predation and competition offer a possible explanation.

Estudio sinóptico del zooplancton de los principales cauces y tributarios del valle aluvial del Río Paraná: Tramo Goya‐Diamante (II Parte)

During a period of high water level, samples of Zooplankton from the main course of Parana river, side‐arms and tributaries were obtained (25 sampling stations). The main course, characterized by high discharge and current velocity of water, showed a small number of species, most of them planktonic, and a low abundance of organisms (X: 10 720 ind m3). The side‐arms and tributaries showed lower discharge and current velocity, together with both a higher number of species and abundance (X: 15 190 and 320 435 ind m3, respectively). In the tributaries, with their high concentrations of salts, a particular faunistic composition was registered. The similarities among these environments were calculated and the data of this study are compared with the other study carried out during a mean water level.

A simple and inexpensive trap-tube sampler for zooplankton collection in shallow waters

The paper describes a new type of zooplankton sampler, which combines the concepts of the Pennak core sampler and the Schindler-Patalas plankton trap. The new sampler, called Trap Tube Sampler, consists of a PVC water pipe (1.5–2.0 m, long; 10 cm diameter) provided, at the bottom end, of a filtering unit and closing mechanism which alternatively closes the mouth of the tube and the mouth of the filtering unit. The new device is particularly suitable for collecting samples from the entire water column in shallow vegetated water bodies, fish ponds and mesocosm tanks.

Diversity of rotifera (Monogononta) in wetlands of Río Pilcomayo National Park, Ramsar Site (Formosa, Argentina)

The rotifers at this Ramsar site were inventoried for the first time. A total of 114 taxa, belonging 30 genera were found in samples collected from four aquatic habitats in the Río Paraguay basin, in northern Argentina. The rotifer fauna is characterized by a large proportion of cosmopolitan and tropicopolitan species and few species endemic to the Neotropical Region (5%). In the list, 22% of the taxa are new to the Argentine fauna. Colurella sinistra Carlin is a new record to the Neotropical fauna. Ecological and distributional notes on selected species are included.The rotifers at this Ramsar site were inventoried for the first time. A total of 114 taxa, belonging 30 genera were found in samples collected from four aquatic habitats in the Río Paraguay basin, in northern Argentina. The rotifer fauna is characterized by a large proportion of cosmopolitan and tropicopolitan species and few species endemic to the Neotropical Region (5%). In the list, 22% of the taxa are new to the Argentine fauna. Colurella sinistra Carlin is a new record to the Neotropical fauna. Ecological and distributional notes on selected species are included.

The effect of an invading filter-feeding bivalve on a phytoplankton assemblage from the Paraná system: a mesocosm experiment

The effect of different concentrations of the bivalve Limnoperna fortunei on the algal density and structure and its filtration rate was estimated in a mesocosm experiment. The experiment was carried out using containers of 200 L and three treatments: Control (without bivalves), C1 (with 128 individual bivalves), and C2 (with 256 individual bivalves). Decrease in phytoplankton density was detected in bivalve treatments after 6 h. A decrease of 52% and 86% of the initial density was measured in C1 and C2, respectively, after 48 h. All algae groups showed substantial decrease in densities (>60%) and the composition of the algae assemblages changed in the presence of the bivalve. In particular, there was an increase in the density of Flagellates. The maximum estimated bivalve filtration rate was 357 mL ind−1 h−1 at 28°C. Our results suggest that the invading bivalves could significantly affect both the plankton density and assemblage structure in natural systems.

Horizontal distribution of rotifers in a subtropical shallow lake (Paraná floodplain, Argentina)

Fil: Jose, Susana Beatriz. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Santa Fe. Instituto Nacional de Limnologia. Universidad Nacional del Litoral. Instituto Nacional de Limnologia; Argentina

Vulnerability of microcrustaceans to predation by the invasive filter-feeding mussel Limnoperna fortunei (Dunker)

Limnoperna fortunei is an Asian mussel introduced to South America around 1990. One of the most important impacts of this invader is probably its grazing on the plankton. In this study we evaluate the vulnerability of several planktonic microcrustaceans from the Paraná River floodplain to predation by adult L. fortunei. We conducted 2-h laboratory feeding experiments where the bivalves were offered microcrustaceans differing in overall body shape, size, and locomotive abilities. Ingestion and clearance rates for each taxon were estimated. Results suggest that, in addition to detritus and phytoplankton, microcrustaceans may be a very important food item for this invasive mollusc. Limnoperna fortunei can prey on larger organisms (up to 1100 µm) than Dreissena polymorpha, the European and North American invasive mussel.

New Data on the Distribution of Kellicottia bostoniensis (Rousselet, 1908) (Rotifera: Monogononta: Brachionidae): Its Presence in Argentina

Abstract The discovery of this species in plankton samples taken at five stations in the Iguazu River and Uruguay River (in a reservoir and an affluent) is reported. Data on the morphology and measurements of individuals collected are shown. This species had previously been registered in Brazil, South America, where it has dispersed widely. The Iguazu River, tributary of the Parana River, and the Uruguay River could constitute an important dispersal path from Brazilian territory to aquatic environments of Del Plata basin which contains 85% of the freshwater of Argentina.

Zooplankton richness, abundance and biomass of two hypertrophic shallow lakes with different salinity in central Argentina

The zooplankton of lakes is controlled by biological and physico-chemical parameters. Among the former, predation by fish can determine the replacement of large-sized species by small-sized ones and among the latter, salinity exerts negative effects on richness and abundance. Since it has been suggested that saline lakes without fishes have higher zooplankton biomass than low salinity ones, the aim of this study was to determine the richness, abundance and biomass of zooplankton in two lakes with different salinity and test the hypothesis that in the presence of zooplanktivorous fishes and at equal concentrations of nutrients and chlorophyll-a, saline lakes have higher biomass than those with low salinity. The study was conducted in two shallow lakes of the Province of La Pampa (central Argentina): a subsaline lake and a hyposaline lake, which shared high concentrations of chlorophyll-a and total phosphorus, reduced transparency and presence of planktivorous fish. Zooplankton richness was different and higher in the subsaline lake, whereas abundance and total biomass were similar, even when the taxonomic groups were considered separately. It is suggested that the presence of a halotolerant planktivorous fish controlled the size of zooplankton due to the predation on larger species and prevented the development of higher biomass in the saline lake, which is an important difference from previously recorded situations. This study shows that, regardless of the differences in salinity, the top-down effect in the food chain may have been a factor that equalized the zooplankton biomass by allowing only the development of small species and highlights the possible importance of fish predation in determining chlorophyll-a concentrations and water transparency.