Relationship between the zoo- and phytoplankton biomasses in a saline lowland river (Argentina): a short-time-scale analysis

Abstract

Short-time-scale (days) lotic investigations during low-discharge conditions are appropriate for elucidating trophic relationships within plankton. The objectives of this study were to determine the successional changes in the zooplankton biomass, the relationship of that biomass to physical parameters and palatable phytoplankton species, and to evaluate the observational time scale. Plankton samples were taken thrice weekly at two sampling stations in the Salado River lower sector (Buenos Aires province, Argentina). Since almost one-third of the country's agricultural and cattle productions come from the Salado-River basin with their resulting impacts (nutrients, suspended material) in the basin, limnological research has been conducted there during recent decades. To estimate grazing, we employed three models and also the relationship between the zoo-and nanoplankton biomasses. The seasonal temperature and conductivity changes indicated three clearly different periods and were the main parameters driving the seasonal succession of the zooplankton. During the first period, the total zooplankton biomass was less than in the other two, with the tintinnids predominating. Later, the rotifers became prevalent with a predomination by Brachionus plicatilis and Keratella tropica. The grazing pressure of the r-strategy dominated zooplankters was highly variable. Zooplankter-species replacement by those of different grazing efficiencies promoted changes in the phytoplankton structure and nanoplankton biomass. A top-down effect on the total phytoplankton biomass by the zooplankton was not detected, though an abundance diminution for certain palatable algae was observed. The biomass of the nanoplankton species was significantly related to the total zooplankton biomass, with the highest rotifer values being associated with an exponential decrease in the nanoplankton biomass.

Estructura y dinámica del bacterioplancton en cuatro lagunas pampeanas de la cuenca del río Salado (Buenos Aires, Argentina)

“…Dentro de la Región Pampeana se encuentra la cuenca del río Salado, una de las más extensas e importantes de la República Argentina (Bettolli et al 2009). Esta cuenca presenta un gran número de lagunas asociadas al río, con diferente grado de conectividad; esto hace que todo el sistema actúe de forma interconectada dependiendo de los ciclos hídricos (Gabellone et al 2001(Gabellone et al , 2003(Gabellone et al , 2014. Diversas actividades humanas como la pesca, la agricultura, el pastoreo, el transporte, la recreación y el turismo requieren de los recursos naturales que las lagunas proveen y, por lo tanto, del mantenimiento de sus condiciones ecológicas, su protección y manejo (Malvárez and Bó 2004).…”

Influence of temperature and conductivity on the life-history characteristics of a pampean strain of Brachionus plicatilis

“…In Argentina, the species has been recorded in many localities (Ferrando and Claps 2016); but a high abundance has been noted throughout the annual cycle in temporary and permanent saline shallow lakes of the La Pampa province (Echaniz et al 2006, 2013, Vignatti et al 2012, and also in lotic environments such as the shallow lakes of the Santa Fe province, those being characterized by conductivities between 2.5 and 7.0 mS.cm -1 depending on associated saline river discharges (José de Paggi and Paggi 1998, José de Paggi and Devercelli 2011). In the Buenos Aires province, B. plicatilis is spatiotemporally predominant in the Salado River basin during extreme droughts or with salinities above 3.0 mS.cm -1 during the summer or winter periods (at temperatures lower than 12 °C) promoting a concurrent general decrease in the specific richness of zooplankton (Gabellone et al 2013(Gabellone et al , 2014, but the species has also been recorded in low densities at conductivities of less than 2.0 mS.cm -1 and temperatures ranging from 7 to 30 °C (Claps et al 2009). Bazzuri (2016) reported both types "L" and "S" of B. plicatilis evaluating morphological attributes in canals and tributaries located at headwaters of the Salado River basin.…”

Succession of microconsumers in waterlogged pampean soils (Buenos aires, Argentina) and its significance for nearby wetlands

“…In the Salado-River basin, several investigations on plankton have been carried out during the last decades (Claps et al 2009;Gabellone et al 2014). When the plankton in a backwater pond was recorded monthly in the lower basin (Gabellone et al 2001;Solari et al 2002), an input of biota from that pond was detected in the river; and the zooplankton structure downstream from that lentic environment was found to be similar to that recorded in the pond itself suggesting a close linkage amongst habitats.…”