ABSTRACT. Temporary water bodies can remain active as such for varying periods. However, they are reservoirs (as "egg banks") of species adapted to these special conditions. In central Argentina, there are numerous temporary lakes, which have only recently begun to be studied. The aim of this work was to describe the succession of changes in diversity, abundance and biomass of zooplankton as well as in the environment, over a period of eleven months, as from the filling of a temporary saline lake, and test the hypothesis that i) salinity affects negatively the richness and abundance but positively the biomass, and ii) due to changes in environmental conditions produced by advancing the hydroperiod, different species emerge from the egg bank at different times. At the beginning, when salinity was reduced and the concentration of chlorophyll-a was higher, we recorded the highest diversity, due mainly by less tolerance species. Later, as salinity increased, the macrophyta Ruppia cirrhosa developed and covered 90% of the surface of the lake, the concentration of chlorophyll-a decreased and the water transparency increased. The zooplankton richness decreased and the community was integrated only by halotolerant species. In the first two months, there was an increased replacement of species, indicated by the high value of Whittaker's beta diversity index (0.63), the density was high, with a predominance of microzooplankton, so the registered biomass was relatively reduced. Then, abundance decreased markedly, and was mostly dominated by macrozooplankton, so the biomass increased. When salinity exceeded 11 g L -1 , there was a predominance of the halophilic cladoceran Daphnia menucoensis, a species of ecological importance because it's high grazing pressure on phytoplankton. In this study, in addition to the modulating effect of salinity on the richness, abundance and zooplankton biomass, it was verified that the diversity present in the egg bank of temporary saline lakes is higher than that recorded in the water column at any time during hydrophases. Keywords: temporary lakes, saline lakes, Daphnia menucoensis, egg bank, central Argentina.Diversidad zooplanctónica y su relación con cambios ambientales luego del llenado de una laguna salina temporaria de la región semiárida de La Pampa, Argentina RESUMEN. Los cuerpos de agua temporarios pueden permanecer activos durante períodos variables, pero son reservorios ("bancos de huevos") de especies adaptadas a estas especiales condiciones. En el centro de Argentina existen numerosos lagos temporarios, que sólo recientemente han comenzado a ser estudiados. El objetivo de este trabajo fue describir la sucesión de cambios en la diversidad, abundancia y biomasa de zooplancton y en los parámetros ambientales, durante once meses, a partir del llenado de un lago salino temporario y probar las hipótesis de que i) la salinidad afecta negativamente la riqueza y abundancia pero positivamente a la biomasa y ii) debido a los cambios ambientales producidos al avanzar el hidroperíodo, difer...

Moina macrocopa is common in eutrophic water bodies. Two subspecies have been described: M. macrocopa macrocopa (Straus, 1820), whose original distribution was restricted to the Old World, and M. macrocopa americanaGoulden, 1968, recorded only in North America. In 1994, the species was found in Bolivia, and in 1997 it was found in the northeast of Argentina. As the specimens belonged to M. macrocopa macrocopa in both cases, the authors suggested that it may have been introduced from the Old World by anthropogenic means. The aim of this study was to assess the distribution of M. macrocopa in La Pampa (Argentina), and provide information on its population characteristics under natural conditions. The species was recorded in six out of more than 100 water bodies surveyed; the specimens belong to M. macrocopa macrocopa. Although this species is not considered halophilic, the water bodies where it was found present high salinity (5.7 to 21.8 g.L–1). All are shallow, temporary and hypertrophic due to the agricultural activities carried out in their basins. Densities were between 1 and 312.6 ind.L–1. Size varied between 0.6 and 1.8 mm and some specimens were larger than those of other places. The parthenogenetic fraction predominated and the number of eggs ranged between 2 and 23. No correlations were found between density, size, or number of eggs and the environmental parameters studied. The presence of M. macrocopa in Pampean lakes could be due to the introduction of fish from hatcheries in the province of Buenos Aires, where it is used as food. Considering that the invasive character ofM. macrocopa has been recognized and that this study found that it is tolerant to a wide range of environmental conditions, attention should be paid to a possible displacement of its native congeneric species, typical of saline and temporary water bodies 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.

Boeckella poopoensis Marsh, 1906 is the dominant copepod in saline lakes from northern Patagonia to southern Peru. It is a tolerant species, which has been registered at salinities between 20 and 90 g.L -1 , and is important because it integrates the diet of flamingos and fishes of commercial and sport interest. The aims of this study were to analyze the characteristics of populations of B. poopoensis in the central region of Argentina and to establish their relationships with environmental parameters. Monthly samples during 2007 were taken in four temporary lakes of La Pampa province. Environmental parameters and density, size, biomass, number and size of eggs were determined. The salinity ranged between 13.38 and 32.90 g.L -1. In three lakes that had previously continuously contained water, B. poopoensis was registered throughout the whole study. In the fourth lake, which was filled in January, it was present only when salinity exceeded 15 g.L -1. The population of the lake that was filled differed from that of the other lakes in terms of the density and biomass of adults and copepodites. The number of ovigerous females represented a higher percentage of the population during the colonization of the lake that had been dried and these produced the highest number of eggs. In the three lakes in which B. poopoensis was always recorded, its characteristics were more influenced by the availability of food than by temperature or salinity. It was found that the strategies of the species vary throughout the hydroperiod; at the beginning, thrives when the salinity rises and impedes the presence of less tolerant species. At this point, the production of relatively small eggs is high, allowing rapid colonization. When the lakes become relatively stable, B. poopoensis allocates more energy to reach larger sizes and although egg production is not so high, they are larger, allowing it to maintain stable populations. Keywords: Boeckella poopoensis, halophilic copepods, saline lakes, temporary lakes. Resumen: Boeckella poopoensis Marsh, 1906 es el copépodo dominante en lagos salinos desde el norte de Patagonia hasta el sur del Perú. Es una especie halotolerante registrada con salinidades entre 20 y 90 g.L -1 y es importante dado que integra la dieta de flamencos y de peces de interés comercial o deportivo. El objetivo del estudio fue analizar características de poblaciones de B. poopoensis en la región central de Argentina y establecer sus relaciones con los parámetros ambientales. Durante 2007 se tomaron muestras mensuales en cuatro lagos temporarios de la provincia de La Pampa. Se determinaron parámetros ambientales y la densidad, espectro de tallas, biomasa, número y tamaño de los huevos. La salinidad varió entre 13,38 and 32,90 g.L -1. En tres lagos que habían contenido agua en forma continua, B. poopoensis se registró durante todo el estudio. En el cuarto, que se llenó en enero, sólo estuvo presente cuando la salinidad superó 15 g.L -1. La densidad y biomasa de los adultos y copepoditos de la población del la...

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