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

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.Fil: Echaniz, Santiago Andrés. Universidad Nacional de La Pampa. Facultad de Ciencias Exactas y Naturales; ArgentinaFil: Vignatti, Alicia María. Universidad Nacional de La Pampa. Facultad de Ciencias Exactas y Naturales; ArgentinaFil: Cabrera, Gabriela Cecilia. Universidad Nacional de La Pampa. Facultad de Ciencias Exactas y Naturales; ArgentinaFil: Jose, Susana Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnología; Argentin

Dynamics of the limnological parameters and zooplankton of La Brava, a shallow lake of the Atuel-Salado-Chadileuvú-Curacó system (La Pampa, Argentina)

La Brava is a shallow lake that is different from others of La Pampa, as it is part of the fluvial system of Desaguadero-Atuel-Salado-Chadileuvú-Curacó rivers. However, dams built upstream disrupt runoff, so water only enters when excessive snowfall in the Andes mountains forces the reservoirs to be opened. Once water enters, it is slowly lost through evaporation, which can lead to drying of the lake. As the ecology of La Brava is unknown, the objective of this study was to determine the limnological parameters, density and taxonomic composition of zooplankton during a period that contained water and salinity increased by evaporation. Samples between January 2009 and November 2010 were taken. The maximum depth (2.1 m) was recorded in October 2009 but declined and in November 2010 was 0.66 m. Na+ and Cl- predominated in ionic composition and the salinity rose from 15.83 to 49.89 g.L-1. The mean transparency was 0.65 m (±0.12) and despite the high concentration of nutrients (TP: 6.02 ±2.87; TKN: 11.17 ±5.92 mg.L-1) the phytoplankton chlorophyll-a concentration was reduced (1.29 ±1.27 mg.m-3). One cladoceran, four copepods and eight rotifers were registered. The greatest diversity was observed during the first month, specially provided by rotifers, when the group reached its greatest density (385.8 ind.L-1), especially given by Brachionus plicatilis Müller, 1786. Increasing salinity affects the diversity, so in June and August 2009 the copepod Boeckella gracilis (Daday, 1902) was recorded, later replaced by the halotolerant Boeckella poopoensis Marsh, 1906. October 2009 was the only occasion when the cladoceran Daphnia menucoensis Paggi, 1996 was registered, in low density (5.7 ind.L-1). Despite their differences with other Pampean environments, in La Brava the typical zooplankton association of the center of the country and northern Patagonia was found, but it differs from another lake of Curacó system where only the halophilic anostracan Artemia persimilis Piccinelli & Prosdocimi, 1968 was registered.Fil: del Ponti, Omar. Universidad Nacional de La Pampa. Facultad de Ciencias Exactas y Naturales; ArgentinaFil: Cabrera, Gabriela Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Confluencia; Argentina. Universidad Nacional de La Pampa. Facultad de Ciencias Exactas y Naturales; ArgentinaFil: Vignatti, Alicia María. Universidad Nacional de La Pampa. Facultad de Ciencias Exactas y Naturales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Confluencia; ArgentinaFil: Echaniz, Santiago Andrés. Universidad Nacional de La Pampa. Facultad de Ciencias Exactas y Naturales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Confluencia; Argentin

Características limnológicas de una laguna turbia orgánica de la provincia de La Pampa y variación estacional del zooplancton

In La Pampa province, shallow lakes (water bodies of low depth, generally polimictic and with high trophic level) are abundant and broadly distributed. Although previous contributions on these shallow lakes are about their ecology and zooplankton, only recently studies have shed light about nutrient concentrations, chlorophyll a and their influence on the zooplankton biomass. It has also been determined that phosphorus and nitrogen concentrations are higher than other shallow lakes of similar characteristics from other regions. The objectives of this contribution are to perform a limnological characterization of an extensive shallow seepage lake with medium salinity and high trophic level of the east-central region of La Pampa province, strongly influenced by human activity. We also present information on the taxonomic composition and abundance and biomass variations of the zooplankton. We took monthly samples from December 2005 to December 2006. In the past, this lake was a temporary lake, but recently it receives water from sewage treatment plants of Santa Rosa city and its pluvial drainages. This lake has now an important tourist and recreational value related to its condition of permanent lake and the presence of silversides (Odontesthes bonariensis). The zooplankton specific richness (15 taxa) was lower than other organic turbid shallow lakes of La Pampa, but closer to the observed in other high salinity shallow lakes. Another common feature with shallow saline lakes of La Pampa was the prevalence, among the microcrustaceans, of the halophilic calanoid Boeckella poopoensis. Cladocerans, on the other hand, were rarely registered; they had very low abundances and they were small-sized, since they could not prosper related to the predatory pressure by the planktivorous fish that inhabit this lakeInstituto de Limnología "Raúl A. Ringuelet

Associations of ostracods in shallow lakes in the northeast of La Pampa province (Argentina)

Los lagos someros son frecuentes en La Pampa. Aunque muchas características de su biota son conocidas, la información sobre la distribución y ecología de los ostrácodos es escasa, a pesar de su importancia como indicadores biológicos y en actuopaleontología. El objetivo de este estudio es conocer la composición taxonómica, la densidad de ostrácodos y sus relaciones con parámetros ambientales en lagos del noreste de La Pampa. Se estudiaron cinco lagos desde septiembre de 2016 hasta marzo de 2017. Se tomaron muestras de sedimentos superficiales e in situ se midieron: conductividad, temperatura y transparencia y se tomaron muestras para determinar salinidad, pH y composición iónica. Los lagos difirieron en su salinidad, composición iónica y transparencia. Se registraron diez taxa, algunos hallados previamente en la provincia de Buenos Aires (Heterocypris similis, Heterocypris incongruens, Cypridopsis vidua y Chlamydotheca incisa), la cuenca de Llancanelo (H. incongruens y C. vidua) y lagos del norte de Patagonia (C. incisa, C. vidua, Potamocypris unicaudata, H. incongruens y Amphicypris argentiniensis). Se comprobó la influencia de la salinidad ya que algunas especies (A. argentinensis, Limnocythere rionegroensis y Limnocythere titicaca) se encontraron sólo en el lago más salino. La existencia en La Pampa de tres ecorregiones diferentes (Llanura Pampeana, Espinal y Estepa Patagónica) y la presencia en los lagos estudiados de ostrácodos del noroeste argentino (L. titicaca), de la llanura bonaerense (H. similis, H. incongruens) y otras de Patagonia (L. rionegroensis), permitiría afirmar que los lagos de La Pampa están en una zona de transición entre faunas diferentes.Shallow lakes are common in the center of Argentina. Although many characteristics of its biota are known, information on the distribution and ecology of ostracods is scarce despite their importance as biological indicators and in actuopaleontology. The objective of this study was to determine the taxonomic composition, the density of ostracods, and their relationships with environmental parameters in lakes in the northeast of La Pampa. Five aquatic ecosystems were studied from September 2016 to March 2017. Samples of superficial sediments were collected, and conductivity, temperature, and transparency were measured in situ. Water samples were collected to determine salinity, pH, and ionic composition. The lakes differed in salinity, ionic composition, and transparency. Ten taxa were registered, some previously found in the province of Buenos Aires (Heterocypris similis, Heterocypris incongruens, Cypridopsis vidua, and Chlamydotheca incisa), the Llancanelo basin (H. incongruens and C. vidua), and North Patagonia lakes (C. incisa, C. vidua, Potamocypris unicaudata, H. incongruens, and Amphicypris argentiniensis). The influence of salinity was verified because some species (A. argentinensis, Limnocythere rionegroensis, and Limnocythere titicaca) were found only in the most saline lake. The existence in La Pampa of three different ecoregions (Pampean Plains, Espinal, and Patagonian Steppe) and the presence of ostracods in the studied lakes of northwestern Argentina (L. titicaca), the Buenos Aires province plain (H. similis, H. incongruens), and Patagonia (L. rionegroensis) allowed for affirming that the lakes of La Pampa are in a transition zone among different ostracods faunas.Fil: Kihn, Romina Gisela. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Ciencias de la Tierra y Ambientales de La Pampa. Universidad Nacional de La Pampa. Facultad de Ciencias Exactas y Naturales. Instituto de Ciencias de la Tierra y Ambientales de La Pampa; ArgentinaFil: Echaniz, Santiago Andrés. Universidad Nacional de La Pampa. Facultad de Ciencias Exactas y Naturales; ArgentinaFil: Vignatti, Alicia María. Universidad Nacional de La Pampa. Facultad de Ciencias Exactas y Naturales; ArgentinaFil: Cabrera, Gabriela Cecilia. Universidad Nacional de La Pampa. Facultad de Ciencias Exactas y Naturales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Stella, Cesar A.. Museo Provincial de Ciencias Naturales; Argentin

Tolerancia a la salinidad de dos cladóceros halófilos autóctonos: Daphnia menucoensis y Moina eugeniae (Artropoda, crustacea)

The zooplankton of the saline lakes of central Argentina includes several native species of crustaceans. Among cladocerans, Daphnia menucoensis Paggi, 1996 and Moina eugeniae Olivier, 1954 are two of the most frequent species in these environments. However, there is no information on their ecophysiological aspects, such as tolerance to different salinities, which may contribute to a better understanding of their geographic and temporal distribution. The aim of this study was to determine the survival of neonates of both species by means of 48-h acute tests (without food or renewal of the medium) at 16 and 18 different salt concentrations. The concentration of total dissolved solids at which the most abundant populations of these species were detected under natural conditions was considered as the “control” or “optimal concentration”. Moina eugeniae was more tolerant to increased salinity than D. menucoensis, since 62% of the neonates of the former survived up to 31 g.l-1, whereas more than 50% of the individuals of the latter survived up to 24 g.l-1. In salinities below the “control” concentration, the tolerance limit was different to that recorded in the field, since both species survived at concentrations below 1 g.l-1, whereas in natural conditions they were recorded only as from 7 g.l-1 (M . eugeniae) and 5 g.l-1 (D. menucoensis).El zooplancton de los lagos salinos del centro de Argentina incluye varias especies nativas de crustáceos. Entre los cladoceranos, Daphnia menucoensis Paggi, 1996 y Moina eugeniae Olivier, 1954 son dos de las especies más frecuentes en estos ambientes. Sin embargo, no hay información sobre sus aspectos ecofisiológicos, como la tolerancia a diferentes salinidades, que pueden contribuir a una mejor comprensión de su distribución geográfica y temporal. El objetivo de este estudio fue determinar la supervivencia de los neonatos de ambas especies mediante pruebas agudas de 48 h (sin alimentos o renovación del medio) a 16 y 18 concentraciones de sal diferentes. La concentración de sólidos disueltos totales en la que se detectaron las poblaciones más abundantes de estas especies en condiciones naturales se consideró como "control" o "concentración óptima". Moina eugeniae fue más tolerante al aumento de la salinidad que D. menucoensis, ya que el 62% de los neonatos de los primeros sobrevivieron hasta 31 g.l-1, mientras que más del 50% de los individuos de estos últimos sobrevivieron hasta 24 g.l-1. En salinidades por debajo de la concentración de "control", el límite de tolerancia fue diferente al registrado en el campo, ya que ambas especies sobrevivieron a concentraciones por debajo de 1 gl-1, mientras que en condiciones naturales se registraron solo a partir de 7 gl-1 (M. eugeniae) y 5 gl-1 (D. menucoensis)

Comparación de los parámetros limnológicos y el zooplancton de un lago somero salino de La Pampa (Argentina) durante dos ciclos anuales con condiciones ambientales diferentes

In central Argentina the alternation of cycles of rainfall above or below the historic mean is frequent; so, many saline lakes can dry or fill in a short time. As in La Pampa most of the studies on these lakes were limited to annual cycles, the information about variations under different climatic conditions is scarce. The aims of this study were to determine the limnological and zooplankton parameters of a semi-permanent Pampean saline lake during 2013 posterior to its filling after a drought, to compare the information with that obtained in 2007, because the two annual cycles had relatively different environmental characteristics and to test the hypotheses i) in 2013, after filling, scarce tolerant zooplankton species were recorded, replaced by more tolerant ones as salinity increased and ii) species richness in 2013 was greater than that recorded during higher hydrologic stability. Samples were taken between January and December of both years. In 2007 depth was stable and in 2013 it fluctuated markedly. The mean salinity was similar, close to 26 g/L. In 2007 it was stable, but in 2013 rose from 14.3 g/L (January) to 40.4 g/L (December). Transparency was the highest in 2007 (0.76 m ± 0.26) and the lowest in 2013 (0.17 m ± 0.05). The concentration of chlorophyll a in 2007 was lower ( (1.73 mg/ m3 ± 1.25) than in 2013 (38.16 mg/m3 ± 42.33). Species richness showed six species in 2007 and seven species in 2013. In 2007 crustaceans predominated, especially Boeckella poopoensis, but in 2013 rotifers dominated. Among them, Brachionus plicatilis and B. dimidiatus presented a maximum in autumn (1702 and 2062 ind/L, respectively). Daphnia menucoensis was absent during 2013 and the inverse correlation between the density of this cladoceran and chlorophyll a concentration could show its influence on water transparency because of its grazing on phytoplankton. The differences in limnological parameters allow us to know the variability of environmental conditions of a Pampean saline lake and to expand our knowledge about tolerance ranges of some endemic species as B. poopoensis and Moina eugeniae.Facultad de Ciencias Naturales y Muse